eng journal voli ig

1 - 239 Engineering Journal and Workbook, Vol. I, 2nd Ed. Chapter 1 Copyright © 2002 Cisco Systems, Inc.

Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition

Engineering Journal and Workbook Questions and Answers

Chapter 1

Computer Basics Introduction

It is important to be able to recognize and name the major components of a PC for the following three reasons:

• Computers are important network-building devices. • Many networking devices are themselves special-purpose computers, with many

of the same parts as normal PCs.

• For you to view the online curriculum, your own computer must be in working order, which means that you might need to occasionally troubleshoot simple problems in your computers hardware and software.

Concept Questions

Demonstrate your knowledge of these concepts by answering the questions in the Engineering Journal space provided.

• The transistor and the integrated circuit made modern computers possible. Explain why. The invention of a semiconductor transistor opened up many possibilities for making smaller, more reliable computers. Millions of transistors can now be placed on one small piece of semiconductor. Further microminiaturization of integrated circuits leads to widespread use of PCs in homes and businesses.

• If your computer doesn’t power up, what steps might you take to identify and correct the problem? If your computer does not power up as expected, consider verifying the following:

⇒ Power cord is plugged into wall socket.

⇒ Power switch is switched to the on (1) position.

⇒ Motherboard power inlet is securely fastened.


• Explain how to do the following: ⇒ Select the NIC card.

The network card selection should involve consideration of the following:

• Bus type (PCI, ISA, EISA, and so on)

• Network topology (bus, ring, star)

• Medium type (UTP, STP, 10Base2, 10Base5, 10BaseF)

• Transport speed (1 Mbps, 4 Mbps, 10 Mbps, 16 Mbps, 100 Mbps, 1000 Mbps)

⇒ Set the correct IP address. The IP address selected should be on the same network or subnetwork as the other devices that need to be accessed. This should be a unique address that is not currently being used by any other nodes on the local network.

⇒ Adjust the display (if necessary). The display can easily be changed by selecting the display icon from the control panel. Select the setting option and choose the desired resolution and color depth. Click Apply to reflect changes.

⇒ Install and set up the browser. Use the installer program to install and configure your browser. Once installed, add any necessary browser plug-ins such as Flash or Shockwave. Choose your method of connectivity, usually dialup or local-area network (LAN). The first connection attempt after install will invoke the Internet Wizard Utility.

Vocabulary Exercise Chapter 1

Define the following terms as completely as you can. Use the online Chapter 1 or the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition, material for help.

ASCII (American Standard Code for Information Interchange) An 8-bit code (7 bits plus parity) for character representation. Backplane Physical connection between an interface processor or card and the data buses and power distribution buses inside a Cisco chassis. Backplane components Backplane, interface, mouse port, network card, parallel port, and other miscellaneous ports.

Binary The binary number system, or Base 2, is made up entirely of 0s and 1s. Computers use Base 2 to express IP addresses.


Bits Each variable set by a computer is represented as being a 0 or a 1. These 0s and 1s represent a circuit being open or closed, or a capacitor being charged or uncharged. Each 0 and 1 is said to be a bit.

Bus A collection of wires through which data is transmitted from one part of a computer to another. It connects all the internal computer components to the CPU. The Industry Standard Architecture (ISA) and the Peripheral Component Interconnect (PCI) are two types of buses.

Bytes Term used to refer to a series of consecutive binary digits that are operated upon as a unit (for example, an 8-bit byte). Capacitor A capacitor consists of two conducting metal plates separated by an insulating material. Capacitors store energy in the form of electrostatic fields.

CD-ROM drive A compact disk read-only memory drive; a device that can read information from a CD-ROM.

Central processing unit (CPU) The part of a computer that controls all the other parts. It fetches instructions from memory and decodes them. This action may cause it to transfer data to or from memory or to activate peripherals to perform input or output.

Expansion slots An opening in a computer where a circuit board can be inserted to add new capabilities to the computer.

Floppy disk drive A disk drive that can read and write to floppy disks, usually in the 3 ½ 1.44 MB or 5 ¼ 1.2 MB format. Hard disk drive The device that reads and writes data on a hard disk. Two main types of drive interfaces are current in todays computers: the Integrated Drive Electronics (IDE) drive and the Small Computer System Interface (SCSI; pronounced scuzzy) drive. Usually referred to by interface type and capacity (MB or GB; for example, 10 GB SCSI drive).

Integrated circuit (IC) A device made of semiconductor material; it contains many transistors and performs a specific task.

Light emitting diodes (LEDs) A semiconductor device that emits light when a current passes through it. Status lights on hardware devices are typically LEDs.

Local-area network (LAN) LANs consist of computers, network interface cards, networking media, network traffic control devices, and peripheral devices in a single building or geographically limited area. LANs make it possible for businesses that use computer technology to efficiently share items, such as files and printers, and to make communications such as e-mail possible. They tie together data, communications, computing, and file servers.

Microprocessor A silicon chip that contains a CPU.

Monitor connector The part of a video cable that plugs into a port or an interface. SVGA connectors are typically a 15-pin connector.

Motherboard The main printed circuit board of a microcomputer.

Mouse port A port designed to connect a mouse to a PC.


Network 1) Collection of computers, printers, routers, switches, and other devices that are able to communicate with each other over some transmission medium. 2) Command that assigns a NIC-based address to which the router is directly connected. 3) Command that specifies any directly connected networks to be included. Network card 1) An expansion board inserted into a computer so that the computer can be connected to a network. 2) Board that provides network communication capabilities to and from a computer system. Also called an adapter.

NIC (network interface card) Also called a LAN adapter, it plugs into a motherboard and provides a port to connect to the network. A NIC communicates with the network through a serial connection, and with the computer through a parallel connection. Each card requires an IRQ, an I/O address, and an upper memory address to work with DOS or Windows 95/98. An interrupt request line (IRQ) is a signal informing a CPU that an event that needs its attention has occurred.

Parallel port An interface capable of transferring more than one bit simultaneously. It is used to connect external devices, such as printers.

PC components Components found within a personal computer include the motherboard, video card, network adapter, hard drive, CPU, memory, sound card, CD-ROM drive, floppy drive, and power supply. Personal computer subsystems Subsystems of a personal computer include the system bus, CD-ROM drive, CPU, expansion cards, expansion slots, floppy disk drive, hard disk drive, motherboard, and power supply.

Power cord A cord used to connect an electrical device to an electrical outlet to provide power to the device.

Power supply The component that supplies power to a computer.

Printed circuit boards (PCBs) A thin plate on which chips (integrated circuits) and other electronic components are placed.

Protocol 1) Formal description of a set of rules and conventions that govern how devices on a network exchange information. 2) Field within an IP datagram that indicates the upper layer (Layer 4) protocol sending the datagram.

Random-access memory (RAM) Also known as read-write memory, RAM can have new data written into it and stored data read from it. A drawback of RAM is that it requires electrical power to maintain data storage.

Resistor A device made of a material that opposes the flow of electric current.

Read-only memory (ROM) Nonvolatile memory that can be read, but not written, by the microprocessor.

Serial port An interface that can be used for serial communication in which only one bit is transmitted at a time.

Small, discrete components Components that are usually found in a laptop. These components are smallerthe expansion slots become PCMCIA or PC slots, where NICs, modems, hard drives, and other useful devices, usually the size of a thick credit card, can be inserted into the PCMCIA slots along the perimeter.

Solder A conductor that is made up a mixture of lead (Pb) and tin (Sn), and water with ions.


Sound card An expansion card that handles all sound functions.

System unit The main part of a PC; the system unit includes the chassis, the microprocessor, the main memory, the bus, and the ports. It does not include the keyboard or the monitor, or any external devices connected to the computer.

Throughput Rate of information arriving at, and possibly passing through, a particular point in a network system.

Transistor A device that amplifies a signal or opens and closes a circuit.

Video card A board that plugs into a PC to give it display capabilities.

Wide-area networks (WANs) Data communications networks that serve users across a broad geographic area and often use transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples of WAN technologies.

Focus Questions

1. What are the major components of a PC?

Components found within a personal computer include the motherboard, video card, network adapter, hard drive, CPU, memory, sound card, CD-ROM drive, floppy drive, power supply.

3. What is the information flow in an idealized computer?

Boot instructionsStored in ROM until they are sent out. Software applicationsStored in RAM after they are loaded. RAM and ROMConstantly talk to the CPU through the bus. Application informationStored in RAM while applications are being used. Saved informationFlows from RAM to some form of storage device. Exported informationFlows from RAM and the CPU, through the bus and expansion slots, to the printer, the video card, the sound card, or the network card.

4. What is the relationship of NICs to PCs?

The NIC enables hosts to connect to the network and is, therefore, considered a key network component.

5. Compare PC components with laptop components.

The main difference is that components in a laptop are smallerthe expansion slots become PCMCIA or PC slots, where NICs, modems, hard drives, and other useful devices, usually the size of a thick credit card can be inserted into the PCMCIA slots along the perimeter.


6. What is data throughput and how does it relate to digital bandwidth?

Throughput refers to the actual, measured bandwidth, at a specific time of day, using specific Internet routes, while downloading a specific file. The throughput is often far less than the maximum possible digital bandwidth of the medium that is being used.

7. Why are there different bandwidths?

Some factors that determine throughput and bandwidth include the following: Internetworking devices Type of data being transferred Topology Number of users Users computer Server computer Power- and weather-induced outages Congestion

8. What units measure the quantity of information?

The most basic unit of information is the bit. The basic unit of time is the second. If you want to describe the amount of information flow in a specific period of time, you could use the units bits per second to describe this flow.

9. How do binary numbers represent alphanumeric data?

Alphanumeric characters are converted to data that can travel across the internetwork. The data is put into a packet or a datagram that contains a network header with source and destination logical addresses. These addresses help network devices send the packets across the network along a dynamically chosen path. Each network device must put the packet into a frame. The frame includes a header with the physical address of the next directly connected device in the path. The frame must be converted into a pattern of 1s and 0s (bits) for transmission on the medium (usually a wire).


CCNA Exam Review Questions

The following questions help you review for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, of the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which of the following best defines networking?

a. A set of rules or procedures that are either widely used or officially specified

b. A connection of computers, printers, and other devices for the purpose of communication

c. A set of rules governing how computer workstations exchange information

d. A device connected to a computer to provide auxiliary functions

2. What is a connection of computers, printers, and other devices for the purpose of communication?

a. Peripheral b. Network c. Mainframe d. Protocol

3. Which of the following terms is used in computing to refer to physical parts or equipment?

a. Hardware b. Software c. Protocol d. Network

4. Which of the following terms is used in computing to refer to programs or applications?

a. Hardware b. Software c. Peripheral d. Network


5. Which of the following refers to devices connected to a computer to provide auxiliary functions such as printing, added disk space, scanning, or CD-ROM?

a. Protocol b. Software c. Peripheral d. Network

6. Why are individual PCs not efficient or cost effective for business

applications?

a. Individual PC use requires businesses to duplicate equipment and resources.

b. It is difficult for businesses to communicate quickly or efficiently using individual PCs.

c. It is difficult to provide management for operating individual PCs. d. All of the above.

7. What is a standalone computer?

a. A computer that manages data efficiently b. A computer that shares files and printers with other computers c. A computer that operates independently from other computers d. A computer that has a different operating system

8. What kind of computer operates independently from other computers?

a. Mainframe b. PC c. Mac d. Standalone

9. Why did standalone computers become an inefficient and ineffective way for businesses to operate?

a. Businesses had to duplicate equipment and resources. b. It was difficult to communicate quickly or efficiently using standalone

computers. c. It was difficult to provide management for operating standalone

computers. d. All of the above.


10. What does the term protocol mean in computing terms?

a. A tool that allows Macintosh and PC computers communicate with each other

b. A universal translator that allows different kinds of computers to share data

c. A description of a set of rules and conventions that govern how devices on a network exchange information

d. The language that all the computers on a network must use to communicate with each other

11. Which of the following best defines protocol?

a. A formal description of a set of rules and conventions b. A device connected to a computer to provide auxiliary functions c. A group of people who are assigned to work as a team d. The connection of computers, printers, routers and switches

12. What is a formal description of a set of rules and conventions called?

a. Peripheral b. Protocol c. Standard d. Network

13. Why are protocols important?

a. By setting rules, they allow different types of computers to talk to each other.

b. By consolidating the industry, they save companies money. c. By forming electronic islands, they bypass the sneaker net. d. By using common carriers, they manage data efficiently.

14. What must all computers on a network be able to do for the network to operate properly?

a. Print to a local printer b. Connect to a telephone line c. Use CD-ROMs d. Speak the same language


15. A protocol allows which of the following to be linked into a network?

a. Only PC terminals and workstations b. Only Macintosh computers and peripherals c. Only PCs to a mainframe d. Any type of computer terminal or workstation


Chapter 2

The OSI Model

Introduction

The OSI reference model is a descriptive network scheme whose standards ensure greater compatibility and interoperability between various types of network technologies. Further, the OSI reference model is a way of illustrating how information travels through networks. It is a conceptual framework specifying the network functions that occur at each layer. The OSI model describes how information or data makes its way from application programs (such as spreadsheets) through a network medium (such as wires) to another application program located on another computer on a network.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided. The ISO recognized the need to create a network model that would help vendors create interoperable network implementations and released the OSI reference model in 1984.

• The OSI reference model is a descriptive network scheme whose standards ensure greater compatibility and interoperability between various types of network technologies. Why is such a standard necessary? In the early days of networking, it became harder for networks that used different specifications and implementations to communicate with each other. They realized that they needed to move away from proprietary networking systems. The ISO created a network model that could help vendors create networks that would be compatible with, and interoperate with, other networks.

• The OSI reference model organizes distinct functions of a network into seven numbered layers. Briefly describe what each layer does. Layer 7: The application layer The application layer establishes the availability of intended communication partners. It also synchronizes and establishes an agreement on procedures for error recovery and control of data integrity. Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs. Layer 6: The presentation layer The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system. If necessary, the presentation layer translates between multiple data formats by using a common format. This layer also is responsible for compression and encryption.


Layer 5: The session layer The session layer establishes, manages, and terminates sessions between two communicating hosts. The session layer provides its services to the presentation layer. It also synchronizes dialog between the two hosts presentation layers and manages their data exchange. In addition to session regulation, the session layer offers provisions for efficient data transfer, class of service, and exception reporting of session layer, presentation layer, and application layer problems. Layer 4: The transport layer The transport layer segments data from the sending hosts system and reassembles the data into a data stream on the receiving hosts system. The transport layer attempts to provide a data transport service that shields the upper layers from transport implementation details. The transport layer establishes, maintains, and properly terminates connection-oriented circuits. To provide reliable service, transport error detection and recovery is used as well as information flow control. Layer 3: The network layer The network layer is a complex layer that provides connectivity and path selection between two host systems that might be located on geographically separated networks. Path selection, routing, and logical addressing all take place at the network layer. Layer 2: The data link layer The data link layer provides the transit of data across a physical link. In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network (sometimes called logical) topology, network media access, and error detection. Layer 1: The physical layer The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other, similar, attributes are defined by physical layer specifications.



Datagram Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP datagrams are the primary information units in the Internet.


Encapsulation The wrapping of data in a particular protocol header. For example, Ethernet data is wrapped in a specific Ethernet header before network transit. Also, when bridging dissimilar networks, the entire frame from one network is just placed in the header used by the data link layer protocol of the other network. Frame Logical grouping of information sent as a data link layer unit over a transmission medium. Often refers to the header and trailer that surround the user data contained in the unit (used for synchronization and error control).

Layer 1: Physical The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems.

Layer 2: Data Link This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: the MAC sublayer and the LLC sublayer.

Layer 3: Network This layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs.

Layer 4: Transport This layer is responsible for reliable network communication between end nodes. The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recovery, and information flow control.

Layer 5: Session This layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities. Layer 6: Presentation This layer ensures that information sent by the application layer of one system will be readable by the application layer of another. The presentation layer also is concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.

Layer 7: Application This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.

Packet Logical grouping of information that includes a header containing control information and (usually) user data. Packets are most often used to refer to network layer units of data. Peer-to-peer Peer-to-peer computing calls for each network device to run both client and server portions of an application. Also describes communication between implementations of the same OSI reference model layer in two different network devices. Segment 1) Section of a network that is bounded by bridges, routers, or switches. 2) In a LAN using a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters. 3) Term used in the TCP specification to describe a single transport layer unit of information.


TCP/IP (Transmission Control Protocol/Internet Protocol) Common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of worldwide internetworks. TCP and IP are the two best-known protocols in the suite.

TCP/IP application layer The designers of TCP/IP thought that the higher level protocols should include the session and presentation layer details. They just created an application layer that handles high-level protocols, issues of representation, encoding, and dialog control. The TCP/IP combines all application-related issues into one layer and ensures this data is properly packaged for the next layer. This is also referred to as the process layer.

TCP/IP Transport Layer The transport layer deals with the quality-of-service issues of reliability, flow control, and error correction. One of its protocols, the transmission control protocol (TCP), provides excellent and flexible ways to create reliable, well-flowing, low-error network communications. TCP is a connection-oriented protocol. It dialogues between source and destination while packaging application layer information into units called segments. Connection-oriented does not mean that a circuit exists between the communicating computers (that would be circuit switching). It does mean that Layer 4 segments travel back and forth between two hosts to acknowledge the connection exists logically for some period. This is known as packet switching.

TCP/IP Internet layer The purpose of the Internet layer is to send source packets from any network on the internetwork and have them arrive at the destination independent of the path and networks they took to get there. The specific protocol that governs this layer is called the Internet Protocol (IP). Best path determination and packet switching occur at this layer. Think of it in terms of the postal system. When you mail a letter, you do not know how it gets there (there are various possible routes), but you do care that it arrives.

TCP/IP network layer The name of this layer is broad and somewhat confusing. It also is called the host-to-network layer. Sometimes, its shown as two layers, as in the OSI model. The network access layer is concerned with all the issues that an IP packet requires to actually cross a physical link from one device to a directly connected one. It includes the LAN and WAN technology details, and all the details in the OSI physical and data link layers.

Focus Questions

1. Briefly describe six reasons why a layered network model is used in internetworking?

• It breaks network communication into smaller, simpler parts that are easier to develop.

• It facilitates standardization of network components to allow multiple vendor development and support.

• It allows different types of network hardware and software to communicate with each other.


• It prevents changes in one layer from affecting the other layers so that they can develop more quickly.

• It breaks network communication into smaller parts to make learning it easier to understand.

• It accelerates the development of future networking products.

2. From memory, list the seven layers of the OSI model and briefly describe their function.

Layer 7: ApplicationThis layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity.

Layer 6: PresentationThis layer ensures that information sent by the application layer of one system will be readable by the application layer of another. The presentation layer also is concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer. Layer 5: SessionThis layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities. Layer 4: TransportThis layer is responsible for reliable network communication between end nodes. The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recovery, and information flow control.

Layer 3: NetworkThis layer provides connectivity and path selection between two end systems. The network layer is the layer at which routing occurs.

Layer 2: Data LinkThis layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: the MAC sublayer and the LLC sublayer.

Layer 1: PhysicalThe physical layer defines the electrical, mechanical, procedural and functional specifications for activating, maintaining, and deactivating the physical link between end systems.

3. What is meant by the term peer-to-peer communication?

Each layer of the OSI model at the source must communicate with its peer layer at the destination.


4. Briefly describe the process of data encapsulation using the following terms: data, segment, packet, frame, and bits.

Networks must perform the following five conversion steps to encapsulate data:

• Build the data. As a user sends an e-mail message, its alphanumeric characters are converted to data that can travel across the internetwork.

• Package the data for end-to-end transport. The data is packaged for internetwork transport. By using segments, the transport function ensures that the message hosts at both ends of the e-mail system can reliably communicate.

• Add the network address to the header. The data is put into a packet or a datagram that contains a network header with source and destination logical addresses. These addresses help network devices send the packets across the network along a dynamically chosen path.

• Append (add) the local address to the data link header. Each network device must put the packet into a frame. The frame includes a header with the physical address of the next directly connected device in the path.

• Convert to bits for transmission. The frame must be converted into a pattern of 1s and 0s (bits) for transmission on the medium (usually a wire). A clocking function enables the devices to distinguish these bits as they travel across the medium. The medium on the physical internetwork can vary along the path used. For example, the e-mail message can originate on a LAN, cross a campus backbone, and go out a WAN link on its way toward its destination on another remote LAN.

5. Describe the information that is added to the data packet as it is encapsulated in the transport, network, and data link layers.

Encapsulation wraps data with the necessary protocol information before network transit. Therefore, as the data packet moves down through the layers of the OSI model, it receives headers, trailers, and other information.

6. What is the OSI reference model?

The Open System Interconnection reference model is a network architectural model developed by ISO and ITU-T. The model consists of seven layers, each of which specifies particular network functions such as addressing, flow control, error control, encapsulation, and reliable message transfer. The highest layer (the application layer) is closest to the user; the lowest layer (the physical layer) is closest to the media technology. The two lowest layers are implemented in hardware and software, whereas the upper five layers are implemented only in software. The OSI reference model is used universally as a way to teach and understand network functionality.


7. Will networks that are built following the OSI model be identical?

Networks that are built following the OSI model will not be identical; however, there will be a much greater likelihood for interoperability. The OSI provides vendors with a set of standards that could enable greater compatibility and interoperability between the various types of network technologies. This will allow dissimilar networks to coexist.

8. What process does the OSI model describe?

The OSI model describes the process of breaking down a complex process into smaller, more easily defined steps. This allows for the creation of standards that help provide greater compatibility and interoperability between various types of network technologies.

9. Define medium.

The term medium refers to various physical environments through which transmission signals pass. Common network media include twisted-pair, coaxial, and fiber-optic cable, and the atmosphere (through which microwave, laser, and infrared transmission occurs).

10. What is the importance of the TCP/IP model?

The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light. The TCP/IP model has historical importance, just like the standards that allowed the telephone, electrical power, railroad, television, and videotape industries to flourish.

11. How does the OSI model compare with the TCP/IP model?

The OSI model attempts to explain how various network technologies work together to transport valuable data. The OSI model is protocol independent, unlike the TCP/IP reference model. The U.S. Department of Defense created the TCP/IP reference model, which became the standard that facilitated the growth of the Internet.



The following questions help you prepare for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, of the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I Second Edition.

1. Which of the following best defines standards?

a. A set of rules or procedures that are either widely used or officially specified b. A connection of computers, printers, and other devices for purposes of

communication c. A set of rules that govern how computer workstations exchange information d. A device connected to a computer to provide auxiliary functions

2. What is the OSI model?

a. A conceptual framework that specifies how information travels through networks

b. A model that describes how data makes its way from one application program to another through a network

c. A conceptual framework that specifies which network functions occur at each layer

d. All of the above

3. As described by the OSI model, how does data move across a network?

a. Directly from each layer at one computer to the corresponding layers at another computer

b. Through wires connecting each layer from computer to computer c. Down through the layers at one computer and up through the layers at

another d. Through layers in wires between computers

4. Which best defines the function of the lower layers (called the media layers) of the OSI model?

a. Provide for the accurate delivery of data between computers b. Convert data into the 1s and 0s that a computer understands c. Receive data from peripheral devices d. Control the physical delivery of messages over the network


5. Which of the following describes the host layers of the OSI model?

a. Control the physical delivery of messages over the network b. Make up the lower layers in the OSI model c. Contain data that is more like 1s and 0s than like human language d. Provide for accurate delivery of data between computers

6. Which of the following best describes the purpose of the physical layer?

a. Defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the link between end systems

b. Provides reliable transit of data across a physical link c. Provides connectivity and path selection between two end systems d. Establishes, manages, and terminates sessions between applications

and manages data exchange between presentation layer entities

7. Which layer of the OSI model is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control?

a. Physical layer b. Data link layer c. Transport layer d. Network layer

8. Which layer of the OSI model provides connectivity and path selection between two end systems where routing occurs?

a. Physical layer b. Data link layer c. Network layer d. Transport layer

9. Which layer of the OSI model is responsible for reliable network communication between end nodes and provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recovery, and information flow control?



10. Which layer of the OSI model establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities?

a. Transport layer b. Session layer c. Presentation layer d. Application layer

11. Which layer of the OSI model ensures that information sent by the application layer of one system will be readable by the application layer of another system, is concerned with the data structures used by programs, and negotiates data transfer syntax for the application layer?


12. Which layer of the OSI model identifies and establishes the availability of intended communication partners, synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity?


13. Which of the following best defines encapsulation?

a. Segmenting data so that it flows uninterrupted through the network b. Compressing data so that it moves faster c. Moving data in groups so that it stays together d. Wrapping of data in a particular protocol header

14. What analogy might be used to describe encapsulation?

a. Encapsulation is like a blueprint for building a car. b. Encapsulation is like sending a package through the mail. c. Encapsulation is like building a fence around your backyard. d. Encapsulation is like driving a car to the store to buy groceries.


15. What is a data packet?

a. Logically grouped units of information b. Transmission devices c. Auxiliary function provided by peripherals d. Virtual circuits


Chapter 3

Local-Area Networks Introduction

Local-area networks (LANs) are high-speed, low-error data networks that cover a relatively small geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or another geographically limited area. LANs provide multiple-connected desktop devices (usually PCs) with access to high-bandwidth media. LANs connect computers and services to a common Layer 1 media.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided:

• The network operates within a building or floor of a building. What are the major characteristics of a LAN? A LAN is a high-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters). LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are widely used LAN technologies.

• What are the major components of the average LAN? LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area.



AUI (attachment unit interface) IEEE 802.3 interface between a media attachment unit (MAU) and a network interface card (NIC). The term AUI also can refer to the rear panel port to which an AUI cable might attach, such as those found on a Cisco LightStream Ethernet access card. Also called transceiver cable.

Bridge Device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (Layer 2) of the OSI reference model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame.


Hub 1) Generally, a term used to describe a device that serves as the center of a star topology network. 2) Hardware or software device that contains multiple independent but connected modules of network and internetwork equipment. Hubs can be active (where they repeat signals sent through them) or passive (where they do not repeat, but merely split, signals sent through them). 3) In Ethernet and IEEE 802.3, an Ethernet multiport repeater, sometimes referred to as a concentrator.

IEEE 802.3 IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet. Physical variations of the original IEEE 802.3 specification include 10BASE2, 10BASE5, 10BASE-F, 10BASE-T, and 10Broad36. Physical variations for Fast Ethernet include 100BASE-T, 100BASE-T4, and 100BASE-X.

LAN (local-area network) A LAN is a high-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are widely used LAN technologies.

MAC address Standardized data link layer address that is required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, a MAC-layer address, or a physical address.

MAU (media attachment unit) Device used in Ethernet and IEEE 802.3 networks that provides the interface between the AUI port of a station and the common medium of the Ethernet. The MAU, which can be built into a station or can be a separate device, performs physical layer functions, including the conversion of digital data from the Ethernet interface, collision detection, and injection of bits onto the network. Sometimes referred to as a transceiver. In Token Ring, a MAU is known as a multistation access unit and is usually abbreviated MSAU to avoid confusion.

Media Plural of medium. The various physical environments through which transmission signals pass. Common network media include twisted-pair, coaxial and fiber-optic cable, and the atmosphere (through which microwave, laser, and infrared transmission occurs). Sometimes called physical media.

NIC (network interface card) Board that provides network communication capabilities to and from a computer system. Also called an adapter.

RAM (random-access memory) Volatile memory that can be read and written by a microprocessor.

ROM (read-only memory) Nonvolatile memory that can be read, but not written, by the microprocessor.

Router Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information. Occasionally called a gateway (although this definition of gateway is becoming increasingly outdated).


Switch 1) Network device that filters, forwards, and floods frames based on the destination address of each frame. The switch operates at the data link layer of the OSI model. 2) General term applied to an electronic or mechanical device that allows a connection to be established as necessary and terminated when there is no longer a session to support.

Focus Questions

1. What are the functions and OSI layer of computers, clients, servers, printers, and relational databases?

Devices that connect directly to a network segment often are referred to as hosts. These hosts include computers (both clients and servers), printers, scanners, and many other user devices. The host devices can exist without a network, but its capabilities are greatly limited. Host devices are not part of any layer. They have a physical connection to the network media by having a NIC, and the functions of the other OSI layers are performed in software inside the host. This means that they operate at all seven layers of the OSI model. The basic function of computers on the LAN is to provide the user with an almost limitless set of opportunities. Modern software, microelectronics, and a relatively small amount of money enable you to run word processing, presentation, spreadsheet, and database programs. They also enable you to run a web browser, which gives you almost instant access to information via the World Wide web. You can send e-mail, edit graphics, save information in databases, play games, and communicate with other computers around the world.

2. What is the purpose and OSI layer of network interface cards in a LAN?

NICs are considered Layer 2 devices because each individual NIC throughout the world carries a unique code, called a Media Access Control (MAC) address. This address is used to control data communication for the host on the network. The NIC is the basic hardware component of network communications. It translates the parallel signal produced by the computer into the serial format that is sent over the network cable.

3. What is the appearance and OSI layer of media in a LAN?

The symbols for media vary, as shown in Figure 3-5. For example, the Ethernet symbol is typically a straight line with perpendicular lines projecting from it; the Token Ring network symbol is a circle with hosts attached to it; and for FDDI, the symbol is two concentric circles with attached devices. The basic functions of media are to carry a flow of information, in the form of bits, through a LAN. Other than wireless LANs (that use the atmosphere, or space, as the medium), networking media confine network signals to wire, cable, or fiber. Networking media are considered Layer 1 components of LANs.


4. What is the symbol and OSI layer of a repeater, as it applies to a LAN?

The symbol for repeaters is not standardizedthe symbol shown in Figure 3-9 represents a repeater throughout the First-Year Companion Guide. The purpose of a repeater is to regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media.

5. What is the function and OSI layer of hub, as it applies to a LAN?

Generally speaking, the term hub is used rather than repeater when referring to the device that serves as the center of a network. The purpose of a hub is to regenerate and retime network signals. Whereas a repeater typically has only 2 ports, a hub generally has from 4 to 20 or more ports. Hubs are considered Layer 1 devices because they regenerate only the signal and repeat it out all of their ports (network connections). The symbol for a hub is not standardized; the symbol shown in Figure 3-12 represents a hub throughout the First-Year Companion Guide.

6. What is the symbol and OSI layer of a bridge, as it applies to a LAN?

A bridge is a Layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain. The purpose of a bridge is to filter traffic on a LANto keep local traffic localyet allow connectivity to other parts (segments) of the LAN for traffic that is directed there. Figure 3-15 shows the bridge symbol, which resembles a suspension bridge.

7. What is the function and OSI layer of a switch on a LAN?

A switch is a Layer 2 device just as a bridge is. In fact, a switch is sometimes called a multiport bridge, just like a hub is called a multiport repeater. The difference between the hub and the switch is the same as the difference between a repeater and a bridge: Switches make decisions based on MAC addresses, and hubs dont make decisions at all. Figure 3-18 shows the symbol for a switch. The arrows on top represent the separate paths data can take in a switch, unlike the hub, where all data flows on all paths.

8. What is the appearance and OSI layer of a router on a LAN?

The purpose of a router is to examine incoming packets (Layer 3 data), choose the best path for them through the network, and then switch them to the proper outgoing port. Routers are the most important traffic-regulating devices on large networks. The symbol for a router, shown in Figure 3-20, is suggestive of its two primary purposes: path selection, and switching of packets to the best route. A router can have many different types of interface ports.

9. What is the symbol and OSI layer of a cloud?

The cloud symbol in Figure 3-24 suggests another network, or perhaps the entire Internet. It reminds you that there is a way to connect to that other network (for example, the Internet), but does not supply all the details of either the connection or the network. Because the cloud is not really a single device, but represents a collection of devices that operate at all levels of the OSI model, it could be classified as a Layer 1 through 7 device.


10. What is the function and OSI layer of network segments?

A network segment is commonly defined as an area that makes up a collision domain. Historically, a segment identifies the Layer 1 media that is the common path for data transmission in a LAN. There is a maximum length for data transmission on each type of media. Each time an electronic device is used to extend the length or to manage data on the media, a new physical segment is created.



The following questions help you prepare for the CCNA Exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. What business problem resulting from the proliferation of standalone computers did networks solve?

a. Inability to communicate and lack of management b. Losses due to lack of business by common carriers c. Inefficient use of information technology professionals d. Increasing level of electromagnetic interference

2. What did early networks allow?

a. Common carriers to finally make a profit b. Workers to copy files onto floppy disks and then carry the disks to a

coworkers PC to print c. The duplication of resources to expand d. The easy and efficient sharing of files and printers

3. Which of the following is not a problem that networking helped solve?

a. Lack of network management b. Lack of new hardware and software products c. Duplication of equipment and resources d. Inability to communicate efficiently

4. Why is it desirable to network?

a. Dont have to duplicate equipment and resources b. Makes it easy to communicate quickly or efficiently using standalone

computers c. Makes it easy to provide management for operating standalone

computers d. All of the above


5. Why is networking a variety of networks together difficult?

a. People try to network different types of computer systems together. b. Emerging network technologies use different hardware and software

specifications. c. Incompatibility due to hardware changes. d. Computer designers try to make their own protocols and they are

incompatible.

6. Why are networking standards needed?

a. Many networks now cover wide geographic areas. b. Technologies must be compatible to allow communication. c. Hardware and software are continually being redesigned. d. LANs, MANs, and WANs use different kinds of equipment.

7. Why did networks experience problems in the mid-1980s?

a. Many new network technologies were incompatible. b. Employees preferred sneaker net. c. Common carriers went bankrupt. d. Everyone used the same hardware and software.

8. Why did using different hardware and software cause problems after networks were established?

a. Networks cannot be formed if some people have Macs and others have PCs.

b. Different hardware and software did not provide auxiliary functions for the users.

c. Different hardware and software implementations used in the new technologies were incompatible.

d. Each department or business was not able to act as an electronic island; instead, they were forced to work together.

9. What is a LAN?

a. A network that connects workstations, terminals, and other devices in a geographically limited area.

b. A network that connects workstations, terminals, and other devices in a metropolitan area.

c. A network that serves users across a broad geographic area and often uses transmission devices provided by a common carrier.

d. A network that covers a larger area than a MAN.


10. Which of the following best describes a LAN?

a. A data network connecting workstations, peripherals, terminals, and other devices in a single building or other geographically limited area.

b. A data network that connects workstations, peripherals, terminals, and other devices across a broad geographic area.

c. A data network that connects workstations, peripherals, terminals, and other devices across a metropolitan area.

d. A data network that connects workstations, peripherals, terminals and other devices within a single building.

11. What is a network that connects computer equipment in a single building called?

a. LAN b. WAN c. MAN d. DCN

12. What is a segment of a network?

a. A section consisting of several interconnected computers, such as a LAN b. A physical wire, such as CAT 5 cable of fiber-optic cable c. A single PC that is part of a LAN d. A part of a network


Chapter 4

Layer 1: Electronics and Signals

Introduction

Electricity is a fact of modern life. We use it to perform a variety of tasks. It is brought to our homes, schools, and offices by power lines that carry it in the form of alternating current (AC). Another type of current, called direct current (DC), is the current found in a flashlight, car battery, and on the motherboard of a computer. It is important to understand the difference between these two types of current flow. Direct current flows at a constant value when circuits are turned on. Alternating current rises and falls in current values as power companies manufacture it. When it reaches our homes, schools, and offices, electricity is carried to appliances and machines via wires concealed in walls, floors, and ceilings. Consequently, inside these buildings, AC power-line noise is all around us. If not properly addressed, power-line noise can present problems for a network. In fact, as you will discover the more you work with networks, AC line noise coming from a nearby video monitor or hard disk drive can be enough to create errors in a computer system. It does this by burying the desired signals and preventing a computers logic gates from detecting the leading and trailing edges of the square signal waves. This problem can be further compounded when a computer has a poor ground connection. The third type of electricity is static electricity. This most damaging uncontrollable form of electricity must be dealt with to protect sensitive electronic equipment. Such static discharges can destroy semiconductors and data in a seemingly random fashion as they shoot through a computer like bullets. As it can with problems related to AC line noise, good grounding helps solve problems that arise from electrostatic discharge.

Concept Questions


• Each wire in a cable can act like an antenna. When this happens, the wire actually absorbs electrical signals from other wires in the cable and from electrical sources outside the cable. If the resulting electrical noise reaches a high-enough level, it can become difficult for NIC cards to discriminate the noise from the data signal. When electrical noise on the cable originates from signals on other wires in the cable, this is known as crosstalk. How can you minimize crosstalk? Crosstalk can be avoided by adhering to standard termination procedures, proper installation methods, and use of quality twisted-pair cables. Ensure that termination of the cable endpoint is completed properly. Avoid untwisting the conductive cables and minimize unshielded cable lengths at termination endpoints.


• To ensure optimal performance, it is important for the network media to carry the signal from one device to another with as little degradation as possible. In networking, several factors can cause the signal to degrade. Some of these factors are internal; whereas, others are external. Name some of the factors that can cause a signal to degrade and how to correct the problem. AC line noise creates problems in our homes, schools, and offices. AC line noise coming from a nearby video monitor or hard disk drive can be enough to create errors in a computer system. Electricity is carried to appliances and machines by wires concealed in walls, floors, and ceilings. Consequently, inside these buildings, AC power-line noise is all around us. If not properly prevented, power-line noise can cause problems for a network.

• Inside copper wires, factors such as opposition to the flow of electrons (resistance), opposition to changes in voltage (capacitance), and opposition to changes in current (inductance) can cause signals to degrade. External sources of electrical impulses that can attack the quality of electrical signals on the cable include lighting, electrical motors, and radio systems. These types of interference are referred to as electromagnetic interference (EMI) and radio frequency interference (RFI). How can you protect your network from RFI? You can limit EMI and RFI in a number of ways. One way is to increase the size of the conductor wires. Another way is to improve the type of insulating material used. However, such changes increase the size and cost of the cable faster than they improve its quality. Therefore, it is more typical for network designers to specify a cable of good quality, and to provide specifications for the maximum recommended cable length between nodes. Two techniques that cable designers have used successfully in dealing with EMI and RFI are shielding and cancellation.



Alternating current (AC) Electrical current that reverses its direction regularly and continuously. It is the form of electrical power found in residential and commercial buildings.

AM (amplitude modulation) Modulation technique whereby information is conveyed through the amplitude of the carrier signal. Analog transmission Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency, and phase.

Attenuation Loss of communication signal energy.

Circuits Communications paths between two or more points.


Conductor Any material with a low resistance to electrical current. Any material capable of carrying an electrical current. Digital signal Language of computers comprising only two states, on and off, which are indicated by a series of voltage pulses.

Direct current (DC) Electrical current that travels in only one direction. Direct current is generally used in electronic circuits. Electricity Electrons in certain atoms can be pulled free from the atom and made to flow. This is electricitya free flow of electrons.

Electrons Particles have a negative charge and orbit the nucleus.

Electrostatic discharge (ESD) A flow or spark of electricity that originates from a static source such as a carpet and arcs across a gap to another object.

FM (frequency modulation) Modulation technique in which signals of different frequencies represent different data values.

Impedance The total opposition to current flow (due to AC and DC voltages). The term resistance generally is used when referring to DC voltages. Impedance is the general term, and is the measure of how the flow of electrons is resisted, or impeded. Impedance is represented by the letter Z. Its unit of measurement, like that for resistance, is the ohm (Ω).

Latency 1) Delay between the time a device requests access to a network and the time it is granted permission to transmit. 2) Delay between the time when a device receives a frame and the time that frame is forwarded out the destination port.

Multimeter A tool used to measure voltage, current, and resistance. It generally has two wires for that reason. The black wire is referred to as the ground, or reference ground. A negative terminal on a battery also is referred to as 0 volts, or reference ground.

Neutrons Particles have no charge (neutral), and along with protons, form the nucleus

Oscilloscope An important and sophisticated electronic device used to study electrical signals. Because it is possible to control electricity precisely, deliberate electrical patterns called waves can be created. An oscilloscope graphs the electrical waves, pulses, and patterns. It has an x-axis that represents time, and a y-axis that represents voltage. There are usually two y-axis voltage inputs so that two waves can be observed and measured at the same time.

PM (phase modulation) The phase, or beginning and ending points of a given cycle, of the wave is varied to carry the message.

Propagation Propagation means travel. When a NIC puts a voltage or light pulse onto a physical medium, that square pulse made up of waves travels along the medium (propagates). Propagation means that a lump of energy, representing 1 bit, travels from one place to another. The speed at which it propagates depends on the actual material used in the medium, the geometry (structure) of the medium, and the frequency of the pulses.

Protons Particles have a positive charge, and along with neutrons, form the nucleus.


Focus Questions

1. What are some examples of electrical insulators?

Electrical insulators are materials that allow electrons to flow through them with great difficulty or not at all. Examples of electrical insulators include plastic, glass, air, dry wood, paper, rubber, and helium gas. These materials have stable chemical structures, with orbiting electrons tightly bound within the atoms.

2. What are some examples of electrical conductors?

Electrical conductors are materials that allow electrons to flow through them with great ease. They flow easily because the outermost electrons are bound very loosely to the nucleus and are freed easily. The best conductors are metals, such as copper (Cu), silver (Ag), and gold (Au). All these metals are located in one column of the periodic table and have electrons that are freed easily, making them excellent materials for carrying a current.

3. What are some examples of semiconductors?

Semiconductors are materials where the amount of electricity they conduct can be controlled precisely. These materials are listed together in one column of the periodic chart. Examples include carbon (C), germanium (Ge), and the alloy gallium arsenide (GaAs). The most important semiconductor, the one that makes the best microscopic-sized electronic circuits, is silicon (Si).

4. What is silicon made of? Is it an insulator, conductor, or semiconductor?

Silicon is common and can be found in sand, glass, and many types of rocks. The region around San Jose, California, is known as Silicon Valley because the computer industry, which depends on silicon microchips, started in that area. The switches, or gates, inside a microprocessor are made up of semiconductors.

5. Do semiconductors allow the amount of electricity to be controlled?

Semiconductors are materials where the amount of electricity they conduct can be controlled precisely.

6. When does voltage occur?

Voltage, sometimes referred to as Electromotive Force (EMF), is an electrical force, or pressure, that occurs when electrons and protons are separated. The force that is created pulls toward the opposite charge and pushes away from the like charge.

7. What is it called when static, or resting, electrons move and a flow of charges is created?

Electrical current, or current, is the flow of charges that is created when electrons move. In electrical circuits, current is caused by a flow of free electrons. When voltage (electrical pressure) is applied, and there is a path for the current, electrons move from the negative terminal (which repels them), along the path, to the positive terminal (which attracts them).


8. What is the abbreviation for amps?

Current is represented by the letter I. The unit of measurement for current is ampere (amp), and is defined as the number of charges per second that pass by a point along a path.

9. What is the abbreviation for resistance?

Resistance is represented by the letter R. The unit of measurement for resistance is the ohm. The symbol comes from the Greek letter omega (Ω).

10. What is the difference between AC and DC?

Alternating current (AC) is one of the two ways in which current flows. AC voltages vary with time by changing their polarity, or direction. AC flows in one direction, and then reverses its direction and repeats the process. AC voltage is positive at one terminal and negative at the other; then, it reverses its polarity and the positive terminal becomes negative and the negative terminal becomes positive. This process repeats itself continuously. Direct current (DC) is the other way in which current flows. DC always flows in the same direction, and DC voltages always have the same polarity. One terminal is always positive, and the other is always negative. They do not change or reverse.

11. How do you measure impedance? What is its abbreviation?

Impedance is the total opposition to current flow (due to AC and DC voltages). The term resistance generally is used when referring to DC voltages. Impedance is the general term, and is the measure of how the flow of electrons is resisted, or impeded. Impedance is represented by the letter Z. Its unit of measurement, like that for resistance, is the ohm.

12. What three components are necessary to make up a circuit, and how do they allow the control of current?

Currents only flow in closed loops called circuits. These circuits must be composed of conducting materials, and must have sources of voltage. Voltage causes current to flow; whereas, resistance and impedance oppose it. Knowing these facts allows people to control a flow of current.

13. What equipment do you use to graph electrical waves, pulses, and patterns?

An oscilloscope graphs the electrical waves, pulses, and patterns. It has an x-axis that represents time, and a y-axis that represents voltage. There are usually two y-axis voltage inputs so that two waves can be observed and measured at the same time.


14. What are some of the characteristics of an analog signal?

An analog signal has the following characteristics:

• Waviness

• A continuously varying voltage-versus-time graph

• Typical of things in nature

• Used widely in telecommunications for more than 100 years The two important characteristics of a sine wave are its amplitude (A), its height and depth, and its period (T), which is the length of time to complete one cycle. You can calculate the frequency (f), wiggleyness, of the wave with the formula f = 1/T.

15. What is the basic building block of information on a data network?

The basic building block of information is 1 binary digit, known as the bit or pulse. One bit, on an electrical medium, is the electrical signal corresponding to binary 0 or binary 1. This can be as simple as 0 volts for binary 0, and +5 volts for binary 1, or a more complex encoding. Signal reference ground is an important concept relating to all networking media that use voltages to carry messages.

16. What are the five sources of noise that can affect a bit on a wire?

NEXT A, thermal noise, impulse/reference ground noise, EMI/RFI, NEXT B

17. At what speed do modern networks typically work?

The speed at which a network propagates depends on the actual material used in the medium, the geometry (structure) of the medium, and the frequency of the pulses. The time it takes the bit to travel from one end of the medium and back is referred to as the round-trip time (RTT). Assuming no other delays, the time it takes the bit to travel down the medium to the far end is RTT/2 The fact that the bit takes a small amount of time to travel along the medium does not normally cause network problems. However, with the ever-increasing data transmission rates of todays networks, sometimes you must account for the amount of time it takes the signal to travel.



The following questions help you review for the CCNA exam. Answers also appear in Appendix A , Answers to the CCNA Exam Review Questions from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which of the following correctly describes the type of signal carried by the network media?

a. Coaxial cable carries pulses of light. b. Unshielded twisted-pair cable carries impedance signals. c. Shielded twisted-pair cable carries electrical impulses. d. Fiber-optic cable carries electrical impulses.

2. Which network media carries pulses of light?

a. Coaxial cable b. Fiber-optic cable c. Unshielded twisted-pair cable d. Shielded twisted-pair cable

3. Which of the following is an external source of degradation of the signal on cabling?

a. EMI caused by electrical motors b. RFI caused by light leakage c. Impedance caused by radio systems d. RFI caused by lighting

4. Which of the following describes cabling signal degradation by an external source?

a. Poor cabling shield connection b. RFI caused by radio systems c. EMI caused by twisting of wires d. Impedance caused by electrical motors

5. What is the cause of crosstalk?

a. Cable wires that are too large in diameter b. Too much noise in a cables data signal c. Electrical motors and lighting d. Electrical signals from other wires in a cable


6. How does crosstalk occur?

a. Two wires are placed in close proximity to each other. b. NIC cards fail to discriminate the noise from the data signal. c. Electrical noise originates from signals on other wires in the cable. d. Wires in a cable absorb electrical impulses from sources outside the

cable.

7. What is a cost-effective way to limit cable signal degradation?

a. Specify the maximum cable length between nodes. b. Increase the size of the conductors in the cabling. c. Improve the type of insulating material. d. Use a braid or foil covering on wires as a shield.

8. How can cable signal degradation be limited in a cost-effective way?

a. Improve the type of insulating material. b. Place same-circuit wires close to each other. c. Use a braid or foil covering on wires as a shield. d. Increase the diameter of the conductor in the cabling.

9. What is cancellation in networking media?

a. The magnetic fields of same-circuit wires cancel each other. b. External magnetic fields cancel the fields inside network cabling. c. Wires in the same circuit cancel each others electrical current flow. d. Twisting wire pairs cancels the electrical impedance in the wires.

10. Which of the following describes cancellation in cabling?

a. Wires in the same circuit cancel each others electrical current flow. b. Twisting wire pairs provides self-shielding within the network media. c. The magnetic fields of wires on different electrical circuits cancel each

other. d. External magnetic fields cancel the fields inside network cabling.


11. Which of the following describes impedance in networking media?

a. Impedance involves resistance and reactance to current caused by signal degradation.

b. Electrical components in the NICs create impedance on the networking media.

c. Signal degradation causes impedance. d. Networking media impedance needs to match the NIC electrical

components.

12. When can impedance degrade the signal in networking media?

a. When resistance opposes reactance b. When cable impedance does not match NIC electrical components c. When networking media is not properly shielded from EMI/RFI

interference d. When cancellation techniques are not employed

13. Which of the following best describes attenuation?

a. The termination of a message b. The interception of a message c. The weakening of a message d. The ignoring of a message

14. How is data transmitted on a network?

a. As hexadecimal code b. As ASCII text c. As 1s and 0s d. As voltage pulses

15. Which best describes the states of digital signals?

a. Alphanumeric b. Octets c. On or off d. Yes or no

16. What does the binary number 1 correspond to in a digital signal?

a. On b. One c. The letter A d. Off


17. What does the binary number 0 correspond to in a digital signal?

a. On b. One c. The letter A d. Off

18. Which best describes a digital signal?

a. A sine wave of normal shape and amplitude b. An electrical technique used to convey binary signals c. Language of computers with only two states, on and off, which are

indicated by a series of voltage pulses d. Transmission sent by a transceiver back to a controller to let it know the

collision circuitry is functional

19. How do computers recognize digital signals?

a. They receive a broadcast signal from the network. b. They look for ARP requests that match their IP address. c. They monitor the network connection for modulations. d. They measure and compare the signals to a reference point.

20. What is the signal reference ground?

a. Neutral contact point where the computer chassis and the network connection meet

b. Point used by devices to measure and compare incoming digital signals c. Device that the name server uses to send messages over the network d. Ground that prevents users from receiving shocks when power fails

21. What is the point used by a device to measure and compare incoming digital signals called?

a. Input point b. Zero point c. Null reference setting d. Signal reference ground


22. How is the signal reference ground established?

a. By connecting the ground wire to the network wire b. By connecting the network wire to the jumper connector c. By connecting the ground plane to the computers cabinet d. By connecting the computer chassis to the network cable

23. What purpose does the computer chassis serve?

a. Prevents electrical short circuits and electrical fires b. Signal reference ground and AC power-line ground c. Amplifies digital signals d. Reduces electromagnetic interference

24. What is the most likely cause of interference on a network?

a. Improper cabling and jack choices b. Electromagnetic interference from radios and other electrical devices c. High voltage device in the vicinity d. Problems with the power ground

25. What is the most likely cause of problems with the power ground?

a. Length of the neutral and ground wires in electrical outlets b. Excessive stripping or untwisting of cable c. Equipment not located in a climate-controlled area d. Poor-quality cabling material used in the network

26. What do long neutral and ground wires in electrical outlets act as?

a. Lightning rods b. Amplifiers for digital signals c. Antenna for electrical noise d. Line signal dampeners

27. How does electrical noise affect networks?

a. Shuts down the network b. Burns out network devices, especially hubs c. Reduces data transmission speed through the network because error-

trapping routines are initiated d. Distorts or buries digital signals to the point that they become

unrecognizable


28. How can the problem of electrical noise be avoided?

a. By limiting the number and type of electrical devices near the LAN b. By working closely with your electrical contractor and the local power

company c. By making sure all electrical devices are FCC and UL listed d. By installing surge suppressors on every network device

29. How can the problem of electrical noise be avoided?

a. By installing surge suppressors on every network device b. By making sure all electrical devices are FCC and UL listed c. By getting a single power transformer dedicated to your LAN d. By limiting the number and type of electrical devices near the LAN

30. How can having a single power transformer dedicated to your LAN reduce electrical noise?

a. You can detect and filter out fluctuations in line voltage before it reaches your LAN.

b. You can specify the size and capacity of the transformer. c. You can place the transformer in a central location. d. You can control how and where devices such as motors or high current

devices are attached.

31. What does installing separate breaker boxes for each office area do to electrical noise?

a. Reduces chance of electrical noise b. Reduces need for surge protectors c. Eliminates need for a generator d. Eliminates need for network rewiring


Chapter 5

Layer 1: Media, Connections, and Collisions Introduction

Networking media are the various physical environments through which transmission signals pass. For computers to communicate encoded information with each other, networking media must physically connect them to each other. The networking media used to connect computers varies. Several kinds of network media can be used to connect computers:

• Coaxial cable

• Unshielded twisted-pair cable

• Shielded twisted-pair cable

• Fiber-optic cable

Concept Questions


• Networking media is defined as the various physical environments through which transmission signals pass. Several types of network media can be used to connect computers. Identify these different types of network media. The following cable types can be used to connect computers:

⇒ Shielded twisted-pair cable

⇒ Unshielded twisted-pair cable

⇒ Coaxial cable

⇒ Fiber-optic cable

• Coaxial cable is a type of network media. Describe how coaxial cable is made. Coaxial cable is made up of a single inner wire conductor that is surrounded by a hollow cylindrical conductor.

• UTP cable is used in a variety of networks. How many wires make up this type of cable? Unshielded twisted-pair (UTP) cable is a four-pair wire medium used in a variety of networks. Eight wires are contained within the outer insulation.


• STP cable combines the techniques of shielding, cancellation, and twisting of wires. What is shielding, and why is it important? Each pair of wires is wrapped in metallic foil. The four pairs of wires are wrapped in an overall metallic braid or foil. (It is normally 150-ohm cable.) STP reduces electrical noise originating inside the cable (crosstalk) and outside the cable (electromagnetic interference [EMI] and radio frequency interference [RFI]).

• Fiber-optic cable is a networking medium. How does it carry signals?

Fiber-optic cable is a networking medium capable of conducting modulated light transmission. Fiber-optic cable does not carry electrical pulses as do other forms of networking media that employ copper wire. Instead, signals that represent bits are converted into pulses of light.

• Various criteria, such as rate of data transfer and expense, help determine which type of media should be used. What media is the fastest and which one is the least expensive? Fiber optic cabling has the fastest possible transport speed; UTP Cat 5 represents the least expensive type of media.

• The data link layer of the OSI model provides access to the networking media and physical transmission across the medium. If you were going to build a network, what media would you use and why? Fiber-optic cabling would be a consideration for all long distances in building-to-building connections. A fiber-optic cabling has the capability to easily transport data at speeds of 10+ Gbps. UTP cabling is generally selected for most office connectivity where occurrences of EMI and RFI are not anticipated. In the industrial and warehouse environments, typically shielded twisted-pair cabling represents the best choice of media to avoid and EMI and RFI. Of course if pricing is not a concern, fiber-optic cabling is the cabling that represents the greatest throughput with the lowest chance of interference.



Bridge Device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (Layer 2) of the OSI reference model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame.

Coaxial cable Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor. Two types of coaxial cable are currently used in LANs: 50-ohm cable, which is used for digital signaling; and 75-ohm cable, which is used for analog signal and high-speed digital signaling.


Fiber-optic cable Physical medium capable of conducting modulated light transmission. Compared with other transmission media, fiber-optic cable is more expensive, but is not susceptible to electromagnetic interference, and is capable of higher data rates. Sometimes called optical fiber.


Repeater Device that regenerates and propagates electrical signals between two network segments.


Shielded twisted-pair (STP) Two-pair wiring medium used in a variety of network implementations. STP cabling has a layer of shielded insulation to reduce EMI. Switch 1) Network device that filters, forwards, and floods frames based on the destination address of each frame. The switch operates at the data link layer of the OSI model. 2) General term applied to an electronic or mechanical device that allows a connection to be established as necessary and terminated when there is no longer a session to support.

Twisted pair Relatively low-speed transmission medium consisting of two insulated wires arranged in a regular spiral pattern. The wires can be shielded or unshielded. Twisted pair is common in telephony applications and is increasingly common in data networks. See also STP and UTP.

Unshielded twisted-pair (UTP) Four-pair wire medium used in a variety of networks. UTP does not require the fixed spacing between connections that is necessary with coaxial-type connections.


Focus Questions

1. Compare and contrast four different Ethernet LAN devices in increasing order of complexity (and typically cost).

Repeaters Repeaters regenerate and retime signals, thereby increasing the distance that signals can travel and still be clearly interpreted at the destination. Repeaters deal only with packets at the bit level; therefore, they are Layer 1 devices. Repeaters are internetworking devices that exist at the physical layer (Layer 1) of the OSI model.

Hubs Hubs combine connectivity with the amplifying and retiming properties of repeaters. It is typical to see 4, 8, 12, and up to 24, ports on multiport repeaters. This allows many devices to be cheaply and easily interconnected.

Bridges Bridges are devices that connect and pass packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (Layer 2) of the OSI reference model. In general, a bridge will filter, forward, or flood an incoming frame based on the MAC address of that frame.

Switches 1) Switches are network devices that filter, forward, and flood frames based on the destination address of each frame. The switch operates at the data link layer of the OSI model. 2) Switch is a general term applied to an electronic or mechanical device that allows a connection to be established as necessary and terminated when there is no longer a session to support.

2. What are some of the characteristics of shielded twisted-pair (STP)?

Shielded twisted-pair cable combines the techniques of shielding and cancellation via the twisting of wires. Each pair of wires is wrapped in metallic foil. The four pairs of wires are wrapped in an overall metallic braid or foil. (It is normally 150-ohm cable.) STP reduces electrical noise originating inside the cable (crosstalk) and outside the cable (electromagnetic interference [EMI] and radio frequency interference [RFI]). Shielded twisted-pair cable shares many of the advantages and disadvantages of unshielded twisted-pair (UTP) cable. STP affords greater protection from all types of external interference, but it is more expensive and difficult to install than UTP.

3. What are some of the characteristics of unshielded twisted-pair (UTP)?

Unshielded twisted-pair cable is a four-pair wire medium used in a variety of networks. Insulating material covers each of the eight individual copper wires in the UTP cable. In addition, each pair of wires is twisted around each other. This type of cable relies solely on the cancellation effect, produced by the twisted wire pairs, to limit signal degradation caused by EMI and RFI. To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies. Like STP cable, UTP cable must follow precise specifications as to how many twists or braids are permitted per foot of cable.


4. What are some of the characteristics of coaxial cable?

Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductorthe two conductors are separated by insulation. In the center of the cable is a single copper wire. A layer of flexible insulation surrounds it. Over this insulating material, a woven copper braid or metallic foil acts as the second of two wires in the circuit. It also acts as a shield for the inner conductor. This second layer, or shield, helps reduce the amount of outside interference. The cable jacket covers this shield.

5. What is the difference between STP and UTP?

UTP cable relies solely on the cancellation effect, produced by the twisted wire pairs, to limit signal degradation caused by EMI and RFI. To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies. UTP uses 100 ohm of resistance; whereas, STP generally has 150 ohms of resistance. STP, unlike UTP cabling, has a metallic braid or foil that adds additional protection against EMI and RFI.

6. What is the difference between STP and coaxial cable?

Both STP and coaxial cable use a metallic braid or foil for added insulation. STP has individual shielding around each individual pair of wires. STP can transfer data at 100 Mbps; whereas, coaxial is limited to 10 Mbps. Coax is terminated using a BNC or AUI connector; whereas, STP cabling is usually terminated with an RJ connector.

7. What is the advantage of fiber-optic cable?

Fiber-optic cabling allows for increased distance while also having the capability of transferring data at a much faster rate than other types of media. Single-mode fiber will support 10 Gbps transmission speeds. Fiber-optic cabling is more secure because data cannot be extracted from the cable inductively. Fiber-optic cabling is also unaffected by RFI and EMI.

8. What are the disadvantages of fiber-optic cable?

The cost of fiber cabling and fiber equipment is significantly greater than that of twisted-pair cabling. Fiber is also very fragile and breaks easily during installation or thereafter. Termination and installation cost is more than double that of twisted-pair cabling.

9. What is the medium for wireless communication? Wireless signals are electromagnetic waves that can travel through the vacuum of outer space and through media, such as the air in our atmosphere. Therefore, no cable medium is necessary for wireless signals.

10. What are TIA/EIA standards?

The TIA/EIA standards specify the minimum requirements for multiproduct and multivendor environments. They allow for the planning and the installation of LAN systems without dictating the use of specific equipment giving LAN designers the freedom to create options for improvement and expansion.


11. What are patch panels?

Patch panels are convenient groupings of RJ-45 jacks. They come in 12, 24, and 48 ports, and typically are rack mounted. The front sides are RJ-45 jacks; the back sides are punch-down blocks that provide connectivity or conducting paths. They are classified as Layer 1 components.

12. How many conductors does an RJ-45 jack have?

An RJ-45 jack/connector is made up of eight conductors, four individual pairs.

13. What is a shared media environment?

A shared media environment occurs when multiple hosts have access to the same medium. If several PCs are attached to the same physical wire or optical fiber, or share the same airspace, for example, they all share the same media environment. Occasionally, you might hear someone say all the computers are on the same wire. It means they all share the same media even though the wire might be CAT 5 UTP, which has four pairs of wire.

14. Where on a network do collisions occur?

If, for example, only one cable interconnects all the devices on a network, the possibility of conflicts with more than one user sending data at the same time is high. The same is true if only non-filtering devices, such as repeaters, connect segments of a network. Ethernet allows only one data packet to access the cable at any one time. If more than one node attempts to transmit at the same time, a collision occurs, and the data from each device suffers damage.

15. What is a collision domain?

The area within the network from where the data packets originated and collided is called a collision domain. All shared media environments are collision domains. One wire might be connected to another wire through patch cables, transceivers, patch panels, repeaters, and hubs. All these Layer 1 interconnections are part of a collision domain.

16. What happens to the signal in a collision?

When a collision occurs, the data packets that are involved are destroyed, bit by bit. In a collision, the signals interfere, or collide, with each other and create a third and invalid state.

17. How do you recognize a collision domain?

If you connect several computers to a single medium that has no other networking devices attached, you have a shared-access situation and you have a single collision domain. Depending on the particular technology used, this situation limits the number of computers that can use that portion of the medium, also called a segment.


18. How do repeaters extend collision domains?

Repeaters regenerate and retime bits, but they cannot filter the flow of traffic that passes through them. Signals that arrive at one port of a repeater are sent out on all other ports. The network on both sides of the repeater is one large collision domain.

19. How do hubs extend collision domains?

The extended collision domain introduced by a hub results in diminished network performance. The degradation in performance depends on the degree of usage of the network by the computers on that network. The hub operates just like the repeater with the addition of numerous nodes, thus increasing the collision domain.

20. Do repeaters filter network traffic?

Both repeaters and hubs are Layer 1 devices; therefore, they perform no filtering of network traffic.

21. What is the four-repeater rule?

The four-repeater rule in Ethernet states that no more than four repeaters or repeating hubs can be installed between any two computers on the network. If followed, the rules guarantee that if a collision occurs, every node in the collision domain knows it has occurred. This is crucial to the successful operation of the network protocol

22. How can the segmentation of collision domains be achieved?

You can reduce the size of collision domains by using intelligent networking devices that break up the domains. Examples of this type of networking device are bridges, switches, and routers.

23. What is linear bus network topology?

The bus topology has all its nodes connected directly to one link, and has no other connections between nodes. Each host is wired to a common wire. One advantage of this topology is that all hosts are connected to each other, and thus can communicate directly. One disadvantage of this topology is that a break in the cable disconnects hosts from each other.

24. What is ring network topology?

A ring topology is a single closed ring consisting of nodes and links, with each node connected to only two adjacent nodes. The topology shows all devices wired directly to each other in what is called a daisy-chain.

25. Are the rings of a dual-ring network topology connected?

The two rings are not connected. A dual-ring topology is the same as a ring topology, except that a second, redundant ring connects the same devices.


26. Where is the node of a star network topology located?

A star topology has a central node with all links to other nodes radiating from it and allows no other links.

27. From a mathematical perspective, where does each node link in an extended star network topology?

An extended star topology has a core star topology, with each of the end nodes of the core topology acting as the center of its own star topology.



The following questions help you prepare for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. What type of fiber-optic cable is required by the TIA/EIA-568B standard for horizontal cabling?

a. Two pair of 100-ohm cable b. Two pair of 150-ohm cable c. Two fibers of 62.5/125 um multimode cable d. Four fibers of 62.5/125 um multimode cable

2. How can you determine which category of UTP cable any cabling belongs to?

a. By looking at the end connectors b. By reading the UL marking c. By measuring the cable diameter d. By the color of the cable sheathing

3. Why do networks need to use an access method?

a. To regulate access to the networking media equitably b. To regulate the access of data into certain parts of networking media c. To keep unwanted, foreign users from having access to the network d. To prioritize data transmissions so that important items have greater

access

4. Which of the following best describes an access method?

a. The method used by software to access network file servers b. The method used to verify users as authorized for access to the network c. The way users access the network d. The way network devices access the network medium

5. Ethernet uses what access method?

a. Token header transmission protocol b. Ethernet does not use an access method c. Carrier sense multiple access collision detect d. Ethernet transmission carrier collision detect


6. Which of the following best describes a collision?

a. The frames from two devices impact and are damaged when they meet on the physical media.

b. Two nodes transmit at the same time and one data packet has priority, so it obliterates the lesser packet.

c. Two data transmissions cross paths on the network media and corrupt each other.

d. A data transmission is corrupted due to an energy spike over the network media.

7. Which of the following best describes a backoff algorithm?

a. A process wherein the network holds up some data so that other, more important data can get through

b. The retransmission delay enforced when a collision occurs c. The signal that a device on the network sends out to tell the other devices

that data is being sent d. A mathematical function performed by networking software that prioritizes

data packets Questions 813 are supplemental and are not found in the Engineering Journal and Workbook.

8. What is most important when considering the type of networking media to use in an installation?

a. Managements wishes b. Availability of networking media from local sources c. Applicable fire, building, and safety codes d. Your experience and expertise

9. Which grade of UTP cabling described in the TIA/EIA-568B standard is used for running CDDI and can transmit data at speeds up to 100 Mbps?

a. Category 2 b. Category 3 c. Category 4 d. Category 5


10. Which grade of UTP cabling described in the TIA/EIA-568B standard is the one most frequently recommended and implemented in installations today?

a. Category 2 b. Category 3 c. Category 4 d. Category 5

11. What is Category 5 UTP cabling suitable for?

a. Transmitting data at speeds up to 10 Mbps b. Transmitting data at speeds up to 100 Mbps c. 10BaseT networks d. Token Ring networks

12. What type of STP cable is required by the TIA/EIA-568B standard for horizontal cabling?

a. Two pairs of 100-ohm cable b. Two pairs of 150-ohm cable c. Four pairs of 100-ohm cable d. Four pairs of 150-ohm cable

13. What type of UTP cable is required by the TIA/EIA-568B standard for horizontal cabling?

a. Two pairs of 100-ohm cable b. Two pairs of 150-ohm cable c. Four pairs of 100-ohm cable d. Four pairs of 150-ohm cable


Chapter 6

Layer 2: Concepts

Introduction

All data sent out on a network is from a source and is going to a destination. After data is transmitted, the data link layer of the OSI model provides access to the networking media and physical transmission across the media, which enables the data to locate its intended destination on a network. In addition, the data link layer handles error notification, network topology, and flow control. If you refer to the OSI model, you see that the data link layer is adjacent to the physical layer. The data link layer provides reliable transit of data across a physical link. This layer uses Media Access Control (MAC) addresses. In so doing, the data link layer is concerned with physical (as opposed to network, or logical) addressing, network topology, line discipline (how end systems will use the network link), error notification, ordered delivery of frames, and flow control. Moreover, the data link layer uses the MAC address to define a hardware or data link address in order for multiple stations to share the same medium and still uniquely identify each other. Before a data packet is exchanged with a directly connected device on the same LAN, the sending device needs to have a MAC address it can use as a destination address.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided.

• Every computer, whether it is attached to a network or not, has a unique physical address; no two physical addresses are ever alike. How is this achieved? Every computer has a unique way of identifying itself. Each computer on a network, has a physical address. No two physical addresses on a network should ever be alike. Referred to as the Media Access Control address, the physical address is located on the network interface card (NIC). A MAC address is a 48-bit address expressed as 12 hexadecimal digits. The first 6 hexadecimal digits of a MAC address contain a manufacturer identification (vendor code), also known as the organizationally unique identifier (OUI). The last 6 hexadecimal digits are administered by each vendor and often represent the interface serial number. The MAC address, or the physical address, is located on a NIC. Therefore, on a network, the NIC is where a device connects to the media. Each NIC, which is located in the data link layer of the OSI reference model, has a unique MAC address.


• On a network, when one device wants to send data to another device, it can open a communication pathway to the other device by using the other devices MAC address. How is this done? In a unicast transmission, a single packet is sent from the source to a destination on a network. First, the source node addresses the packet by using the physical address of the destination node. The package then is sent onto the network, and finally, the network passes the packet to its destination.

• When data is sent out on a network by a source, it carries the MAC address of its intended destination. Does it carry the address of the source? The Layer 2 frame header contains the source MAC address and the next-hop destination MAC address as well. The source MAC address will stay in the frame until the gateway or router removes the frame while routing to the next hop. As this data travels along the networking media, the NIC in each device on the network checks whether its MAC address matches the physical destination address carried by the data packet.



Address Data structure or logical convention used to identify a unique entity, such as a particular process or network device.

Collision domain In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges, and routers do not. CSMA/CD (carrier sense multiple access collision detect) Media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.

Data link layer This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: the MAC sublayer and the LLC sublayer. Sometimes just called link layer. Encapsulation The wrapping of data in a particular protocol header. For example, Ethernet data is wrapped in a specific Ethernet header before network transit. Also when bridging dissimilar networks, the entire frame from one network is just placed in the header used by the data link layer protocol of the other network.


Frame Logical grouping of information sent as a data link layer unit over a transmission medium. Often refers to the header and trailer, used for synchronization and error control, which surround the user data contained in the unit.

Hexadecimal Base 16. A number representation using the digits 0 through 9, with their usual meaning, plus the letters A through F to represent hexadecimal digits with values of 10 to 15. The rightmost digit counts 1s, the next counts multiples of 16 (for instance, 16^2=256 and so on).

Institute of Electrical and Electronics Engineers (IEEE) Professional organization whose activities include the development of communications and network standards. IEEE LAN standards are the predominant LAN standards today. Logical link control (LLC) Higher of the two data link layer sublayers defined by the IEEE. The LLC sublayer handles error control, flow control, framing, and MAC sublayer addressing. The most prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented variants.

Media Access Control (MAC) Lower of the two sublayers of the data link layer defined by the IEEE. The MAC sublayer handles access to shared media, such as whether token passing or contention will be used.

Token Ring Token-passing LAN developed and supported by IBM. Token Ring runs at 4 or 16 Mbps over a ring topology. Similar to IEEE 802.5.

Focus Questions

1. What are three differences between Layer 1 and Layer 2?

Layer 2 of the OSI model provides access to the networking media, which enables the data to reach its intended destination on a network.

⇒ Layer 2 provides transit of data across a physical link.

⇒ Layer 2 uses a system called Media Access Control.

⇒ Layer 2 uses the MAC address, which is the physical address located on a NIC.

⇒ Layer 2 uses framing to organize or group the bits. The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

3. Into what sublayers does the IEEE divide the OSI data link layer?

IEEE has divided the OSI Data link layer into two sublayers: LLC (logical link control) and MAC (Media Access Control).


4. What does the LLC do to the network protocol data?

Higher of the two data link layer sublayers defined by the IEEE, the LLC sublayer handles error control, flow control, framing, and MAC sublayer addressing. The most prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented variants.

5. Convert the decimal number 24,032 to hex.

5DE0

6. How does a computer identify itself on a network?

Every computer has a unique way of identifying itself. Each computer on a network, has a physical address, a 48-bit MAC address.

7. What is the NIC’s role when data is sent out on a network?

When a source device sends data out on a network, the data carries the MAC address of its intended destination. As this data propagates along the network media, the NIC in each device on the network checks to see whether its MAC address matches the physical destination address carried by the data frame. If there is no match, the NIC discards the data frame.

8. What is an advantage and a disadvantage to MAC addresses?

The address is burned into read-only memory and therefore cannot be lost, reset, or conflict with other nodes on a local network. The address is used to identify the node at the data link layer and is referred to as being the physical address. There is no hierarchy or grouping of MAC addressing other than by OUI.

9. Which layer does framing belong to?

The Data link layer

10. What are the names of the six fields found in a single generic frame?

⇒ Frame start field ⇒ Address field ⇒ Length / type / control field ⇒ Data field ⇒ Frame check sequence field ⇒ Frame stop field

11. What are the two parts of a package?

The reason for sending frames is to get higher layer data, ultimately the user application data, from the source computer to the destination computer. The data package you want to deliver includes the message you want to send (the data). The padding bytes are added sometimes so the frames have a minimum lengththis is done for timing purposes.


12. How does the frame check sum help in the delivery of a frame?

In IEEE 802.3 frames, the 2-byte field following the source address is a length field, which indicates the number of bytes of data that follow this field and precede the frame check sequence (FCS) field. This helps identify whether the remote host has received all data intended for this transmission.

13. How does a Token Ring network handle data?

Token Ring networks use deterministic MAC protocols to share access to the network. When a host receives the token, it can transmit data, if it has some, instead of the token. This is called seizing the token. When the transmitted frame comes back around to the transmitter, the station transmits a new token. The frame thus is removed, or stripped, from the ring.



The following questions help you prepare for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions. from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Where do all communications on a network originate?

a. Peripherals b. Sources c. Computers d. Hosts

2. Which of the following best defines a source?

a. Logically grouped units of information b. Network device that receives data c. Computer that operates independently from other computers d. Network device that is sending data

3. What is a source device?

a. A source device receives data and information from other computers in a network.

b. A source device sends data and information to other computers in a network.

c. A source device is information that moves between computers in a network.

d. A source device provides connectivity between computers in a network.

4. Where are all communications on a network being sent?

a. Source b. Computer c. Data link d. Destination

5. Which of the following best defines a destination?

a. Logically grouped units of information b. Network device that is receiving data c. Redundant use of equipment to prevent data loss d. Network device that is sending data


6. What is another name for link layer addresses?

a. IP addresses b. Network addresses c. Logical addresses d. Physical addresses

7. What is another name for link layer addresses?

a. MAC addresses b. IP addresses c. Logical addresses d. Network addresses

8. Where are link layer addresses usually located?

a. In the routing table b. On the NIC c. In the ARP cache d. In the name server tables

9. On which layer of the OSI model are physical addresses located?

a. Presentation layer b. Session layer c. Data link layer d. Network layer

10. Which is true about MAC addresses?

a. Unique for each LAN interface b. Located at the network layer c. Also called logical addresses d. Used to identify host networks

11. Where is the MAC address located?

a. At the network layer b. Burned into ROM at the factory c. In the AUI d. At the MAU interface


12. Which of the following describes the structure of a MAC address?

a. 32-bit network identity plus 32-bit host identity b. Network, subnet, subnet mask, host c. 24-bit vendor code plus 24-bit serial number d. Network code plus serial number

13. Which of the following could be a MAC address?

a. 172.15.5.31 b. 1111.1111.111 c. FFFF.FFFF.FFFF d. 0000.0c12.3456

14. Which best describes carrier sense multiple access collision detect (CSMA/CD)?

a. Devices check the channel to make sure no signals are being sent before transmitting data.

b. Devices transmit data and listen to make sure that they are received properly.

c. Devices transmit a request prior to transmitting data over the network and wait for an all clear reply.

d. Devices monitor the channel continuously to track and manage traffic.

15. Which of the following is not a function of CSMA/CD?

a. Transmitting and receiving data packets b. Decoding data packets and checking them for valid addresses c. Detecting errors within data packets or on the network d. Cleaning up collisions on the network medium


Chapter 7

Layer 2: Technologies

Introduction

Ethernet was developed by Xerox Corporations Palo Alto Research Center (PARC) in the 1970s. Ethernet is the most popular LAN standard today. There are millions of devices, or nodes, on Ethernet LANs. The early LANs required very little bandwidth to perform the simple network tasks required at that timesending/receiving e-mail, transferring data files, and handling print jobs. In 1980, the Institute of Electrical and Electronic Engineers (IEEE) released the IEEE 802.3 specification for which Ethernet was the technological basis. Shortly thereafter, Digital Equipment Corporation, Intel Corporation, and Xerox Corporation jointly developed and released an Ethernet specification (version 2.0) that is substantially compatible with IEEE 802.3. Together, Ethernet and IEEE 802.3 currently maintain the greatest market share of any LAN standard. An Ethernet LAN transports data between network devices, such as computers, printers, and file servers. Ethernet is known as a shared-medium technology; all the devices are connected to the same delivery media. Delivery media refers to the method of transmitting and receiving data. For example, a handwritten letter can be sent (transmitted) using one of many delivery methods, such as the U.S. postal service, Federal Express, or fax. Electronic data can be transmitted via copper cable, thick coaxial cable, thinnet, wireless data transfer, and so on.

Concept Questions


• Ethernet, FDDI, and Token Ring are widely used LAN technologies that account for virtually all deployed LANs. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Because they are widely adhered to, this book covers the Ethernet and IEEE 802.3 LAN standards. Why do you suppose that Ethernet technology is so heavily used? Ethernet is well suited to applications in which a local communication medium must carry sporadic, occasionally heavy traffic at high-peak data rates. Ethernet was considered high-speed when it was first available


• When it was developed, Ethernet was designed to fill the middle ground between long-distance, low-speed networks and specialized, computer-room networks carrying data at high speeds for very limited distances. Ethernet is well suited to applications in which a local communication medium must carry sporadic, occasionally heavy traffic at high-peak data rates. Why is Ethernet so well suited to this kind of traffic?

Ethernet was designed to fill the middle ground between long-distance, low-speed networks and specialized, computer-room networks carrying data at high speeds for very limited distances.

• Today, the term standard Ethernet refers to all networks using Ethernet (a shared-medium technology) that generally conform to Ethernet specifications, including IEEE 802.3. To use this shared-medium technology, Ethernet uses the carrier sense multiple access collision detection (CSMA/CD) protocol to allow the networking devices to negotiate for the right to transmit. What are the major benefits of Ethernet? It was designed to enable sharing resources on a local workgroup level. Design goals included simplicity, low cost, compatibility, fairness, low delay, and high speed.



Access control byte The access control byte contains the priority and reservation fields, a token, and a monitor bit. The token bit distinguishes a token from a data/command frame, and a monitor bit determines whether a frame is continuously circling the ring. The end delimiter signals the end of the token or data/command frame. It contains bits that indicate a damaged frame, as well as bits that indicate whether a frame is the last of a logical sequence.

CSMA/CD (carrier sense multiple access collision detect) Media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3. Data (Ethernet) After physical layer and link layer processing is complete, the data contained in the frame is sent to an upper-layer protocol, which is identified in the type field. Although Ethernet version 2 does not specify any specific padding, in contrast to IEEE 802.3, Ethernet expects at least 46 bytes of data, like 802.3.

Data (IEEE 802.3) After physical layer and link layer processing is complete, the data is sent to an upper-layer protocol, which must be defined within the data portion of the frame. If data in the frame is insufficient to fill the frame to its minimum 64-byte size, padding bytes are inserted to ensure at least a 64-byte frame.


Destination and source addresses The first 3 bytes of the addresses are specified by the IEEE on a vendor-dependent basis. The last 3 bytes are specified by the Ethernet or IEEE 802.3 vendor. The source address is always a unicast (single-node) address. The destination address can be unicast, multicast (group), or broadcast (all nodes).

End delimiter The end delimiter signals the end of the token or data/command frame. It contains bits that indicate a damaged frame, as well as bits that indicate whether a frame is the last of a logical sequence.

Ethernet Baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable types at 10 Mbps. Ethernet is similar to the IEEE 802.3 series of standards.

FDDI (Fiber Distributed Data Interface) LAN standard, defined by ANSI X3T9.5, specifying a 100-Mbps token-passing network using fiber-optic cable, with transmission distances of up to 2 kilometers. FDDI uses a dual-ring architecture to provide redundancy.

Frame check sequence (FCS) This sequence contains a 4-byte CRC value that is created by the sending device and is recalculated by the receiving device to check for damaged frames.

IEEE 802.3 IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet.

Length (IEEE 802.3) The Length field indicates the number of bytes of data that follows this field.

Microsegmentation Division of a network into smaller segments, usually with the intention of increasing aggregate bandwidth to network devices.

MSAU (multistation access unit) Wiring concentrator to which all end stations in a Token Ring network connect. The MSAU provides an interface between these devices and the Token Ring interface of, for example, a Cisco 7000 TRIP. Sometimes abbreviated MAU.

NIC (network interface card) Board that provides network communication capabilities to and from a computer system. Also called an adapter.

Preamble The purpose of the preamble is synchronization. The Ethernet frame includes an additional byte that is the equivalent of the Start of Frame (SOF) field specified in the IEEE 802.3 frame.


Start delimiter The start delimiter alerts each station to the arrival of a token, or data/command frame. This field also includes bit patterns that distinguish the byte from the rest of the frame by violating the encoding scheme used elsewhere in the frame.


Focus Questions

1. What is the size and composition of a token?

Tokens are 3 bytes in length and consist of a start delimiter, an access control byte, and an end delimiter.

2. What does the source address field in an FDDI frame identify?

The source address identifies the single station that sent the frame; source addresses are 6 bytes (like Ethernet and Token Ring).

3. Which field determines whether the frame contains asynchronous or synchronous data?

The Frame Control field indicates the size of the address fields, whether the frame contains asynchronous or synchronous data, and other control information

4. What are two features that are both FDDI and Token Ring share?

The two networks share a few features, such as topology (ring) and media access technique (token passing).

5. What are the three advantages that optical fiber has over copper wiring?

Optical fiber offers several advantages over traditional copper wiring, including such advantages as these:

⇒ Security. Fiber does not emit electrical signals that can be tapped.

⇒ Reliability. Fiber is immune to electrical interference.

⇒ Speed. Optical fiber has much higher throughput potential than copper cable.

6. What network device must all network traffic pass through on a star topology?

When a star topology is used, communication between devices attached to the LAN is via point-to-point wiring to the central link or hub. All network traffic in a star topology passes through the hub.

7. What is the purpose of a NIC?

A network interface card is a Layer 2 device that plugs into a motherboard and provides ports for network connection. This card can be designed as an Ethernet card, a Token Ring card, or an FDDI card. Network cards communicate with the network through serial connections and with the computer through parallel connections. They are the physical connections from workstations to the network.


8. What are two reasons why LANs are segmented?

The primary reason for segmenting a LAN is to isolate traffic between segments and to achieve more bandwidth per user by creating smaller collision domains. Segmentation also accommodates communication between a larger number of devices than could be supported on any single LAN connection.

9. Ethernet uses which access method to detect errors within data packets or on the network?

Ethernet uses CSMA/CD, a media-access mechanism wherein devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3.

10. Why is it cost efficient to have a switched LAN environment?

A switched Ethernet LAN allows a LAN topology to work faster and more efficiently than a standard Ethernet LAN can because it uses bandwidth so efficiently. In a switched Ethernet implementation, the available bandwidth can reach close to 100 percent.



The following questions help prepare you for the CCNA Exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which best describes the data link layer of the OSI model?

a. Transmits data to other network layers b. Provides services to application processes c. Takes weak signals, cleans them, amplifies them, and sends them on

their way across the network d. Provides reliable transit of data across a physical link

2. Which layer provides reliable transit of data across a physical link?

a. Data link b. Physical c. Application d. Transport

3. What processes is the data link layer concerned with?

a. Physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control

b. Establishing, managing, and terminating sessions between applications, and managing data exchange between presentation layer entities

c. Synchronizing cooperating applications and establishing agreement on procedures for error recovery and control of data integrity

d. Providing mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection, recovery, and information flow control

4. Physical addressing and network topology are handled by which layer?

a. Physical b. Presentation c. Data link d. Session


5. On a network, where does a device connect to the media?

a. Ethernet card b. Hub c. Router d. NIC

6. What is another name for the MAC address?

a. Binary address b. Octadecimal address c. Physical address d. TCP/IP address

7. In which layer is the MAC address located?

a. Session b. Data link c. Physical d. Transport

8. What does MAC address stand for?

a. Macintosh Access Capable b. Mainframe Advisory Council c. Media Access Control d. Machine Application Communication

9. Which of the following items is located in the data link layer?

a. Destination b. Peripheral c. Repeater d. MAC address

10. What is required for every port or device that connects to a network?

a. Repeater b. Termination c. MAC or physical address d. ATM switch


11. Which of the following best describes MAC addressing?

a. Addresses reside in the NIC card and are assigned by their manufacturers.

b. Addresses are assigned by the IEEE committee and need to be requested by the network administrator.

c. Addresses are determined by the distance of the computer from the network hub.

d. Addresses are given to every computer when they are manufactured.

12. How does a source device locate the destination for data on a network?

a. The NIC at the destination identifies its MAC address in a data packet. b. A data packet stops at the destination. c. The NIC at the destination sends its MAC address to the source. d. The source sends a unique data packet to each MAC address on the

network.

13. Which of the following best describes internetworking devices?

a. Products that determine the optimal path along which network traffic should be forwarded

b. Products that contain multiple independent, connected modules of network equipment

c. Network connections or a junction common to two or more lines in a network

d. Products used to connect separate networks to each other


Chapter 8

Design and Documentation

Introduction

Of all the organizations mentioned here, the EIA/TIA has had the greatest impact on networking media standards. The EIA/TIA standards were developed with the intent of identifying minimum requirements that would support multiproduct and multivendor environments. Moreover, these standards were developed so that they allow for planning and installation of LAN systems without knowledge of the specific equipment that is to be installed. Therefore, the EIA/TIA standards allow the LAN designer options and room for expansion. Specifically, the EIA/TIA-568B standards for technical performance of the networking media have been, and continue to be, the most widely used. The EIA/TIA standards address six elements of cabling for LAN systems: horizontal cabling, telecommunications closets, backbone cabling, equipment rooms, work areas, and entrance facilities. EIA/TIA-568B defines horizontal cabling as a networking medium that runs from the telecommunications outlet to the horizontal cross-connect. This element includes the networking medium that is run along a horizontal pathway, the telecommunications outlet or connector, the mechanical terminations in the wiring closet, and the patch cords or jumpers in the wiring closet. In short, horizontal cabling describes the networking medium that is used in the area extending from the wiring closet to a workstation. After you successfully run cable in a horizontal cabling run, connections must be made in the wiring closet. A wiring closet is a specially designed room used for wiring a data or voice network. Because a wiring closet serves as a central junction point for the wiring and wiring equipment that is used for connecting devices in a LAN, it is at the center point of a star topology. Typically, the equipment found in a wiring closet can include patch panels, wiring hubs, bridges, switches, and routers. Generally, the wiring closet must be large enough to accommodate the equipment and wiring located in it. Naturally, this varies with the size of the LAN and the types of equipment required to operate it. Equipment required for some small LANs might take up as little space as a large filing cabinet; whereas, a large LAN could require a full-fledged computer room. Finally, the wiring closet must be large enough to accommodate future growth.


Concept Questions


• EIA/TIA standards govern the type of networking media that can be used in the horizontal cabling of LANs. What type of networking media can be used with horizontal cabling?

The TIA/EIA recommends the use of Cat 5 or 5e UTP for horizontal cabling when an Ethernet LAN uses a simple star topology.

• Any time you install cable, it is important to document what you have done. How would you document the kind of cable used in a network?

All cable runs should be documented on a cut sheet, usually located for reference at the supporting IDF.

• A wiring closet is a specially designed room used for wiring a data or voice network. What attributes are necessary for a working wiring closet?

The wiring closet must be large enough to accommodate all the equipment and wiring that will be placed in it and account for future growth.

• The IEEE and the EIA/TIA have established standards that enable you to evaluate whether your network is operating at an acceptable level after installation has been completed. What are some of those standards?

EIA/TIA-568 is a standard that describes the characteristics and applications for various grades of UTP cabling.

TIA/EIA-569 is a standard that specifies the wiring closet requirements.

• Cable testers can perform tests that measure the overall capability of a cable run. Cable testers use a feature called wire map to indicate which wire pairs connect to what pins on lugs and sockets. Describe how you would use a cable tester to measure the capability of the cable run.

It is important to measure the overall length of cable runs. Distance can affect the capability of devices on the network that share the networking media. As you have already learned, cable that exceeds the maximum length specified by TIA/EIA-568-A causes signal degradation. Cable testers, sometimes referred to as time domain reflectometers (TDRs), measure the distance to open-ended, or shorted, cable. They do it by sending an electrical pulse through the cable. The devices then time the signals reflection from the end of the cable. This test is called time domain reflectometry, and can provide distance readings that are accurate to within 61 centimeters.

• If not properly addressed, AC power-line noise can present problems for a network. Why does the noise cause problems for the network?

If the resulting electrical noise reaches a high enough level, it can become difficult for NICs to discriminate the noise from the data signal. This is particularly a problem because most LANs use frequencies in the 1100 megahertz (MHz) frequency region, which happens to be where FM radio signals, TV signals, and lots of appliances have their operating frequencies as well.


• The problem of sags and brownouts can best be addressed through the use of UPSs.


Define the following terms as completely as you can. Use the online Chapter 8 or the Cisco Systems Networking Academy: Engineering Journal and Workbook, Volume I, Second Edition, material for help.

Backbone The part of a network that acts as the primary path for traffic that is most often sourced from, and destined for, other networks.

Catchment areas Zone that falls within area that can be served by an internetworking device such as a hub.

HCC (horizontal cross-connect) Wiring closet where the horizontal cabling connects to a patch panel that is connected by backbone cabling to the main distribution facility.

Hierarchical star Extended star topology where a central hub is connected by vertical cabling to other hubs that are dependent on it.


IDF (intermediate distribution facility) Secondary communications room for a building using a star networking topology. The IDF is dependent on the MDF. MCC (main cross-connect) Wiring closet that serves as the most central point in a star topology and where LAN backbone cabling connects to the Internet.

MDF (main distribution facility) Primary communications room for a building. Central point of a star networking topology where patch panels, hub, and router are located.

Micron Unit of measure equal to one millionth of a meter or one thousandth of a millimeter. Sometimes the symbol µ is used rather than the word micron. Oscillation Secondary signal on top of the 60-Hz waveform. It has a magnitude that ranges from 15 percent to 100 percent of the normal voltage carried on the power line. Patch panel An assembly of pin locations and ports which can be mounted on a rack or wall bracket in the wiring closet. Patch panels act like switchboards, connecting workstation cables to each other and to the outside.

PBX (private branch exchange) Digital or analog telephone switchboard located on the subscriber premises and used to connect private and public telephone networks.

POP (Point of Presence) Point of Presence is the point of interconnection between the communication facilities provided by the telephone company and the building's main distribution facility.


Sag Any decrease of below 80 percent in the normal voltage carried by a power line. A sag is sometimes referred to as a brownout.

Spike Any power impulse lasting between .5 and 100 microseconds and possessing an amplitude over 100 percent of peak power-line voltage. Surge Any voltage increase above 110 percent of the normal voltage carried by a power line.

Focus Questions

1. Where is the patch panel and hub located in a star topology?

The central point is the wiring closet, where the patch panel and the hub must be installed.

2. How much weight per square meter must the floor of the MDF be able to bear?

If there is only one wiring closet in a building, or if the wiring closet serves as the MDF, the floor on which it is located must be capable of bearing the load specified by the installation instructions included with the equipment, with a minimum capability of 4.8 kPA (100lb/ft2). Where the wiring closet serves as an IDF, the floor must be capable of bearing a minimum load of 2.4 kPA (50lb/ft2).

3. What problem could result if the humidity level in the MDF is above 50 percent?

Relative humidity should be maintained at a level between 30 and 50 percent. Failure to adhere to these particular specifications could result in serious corrosion of the copper wires that are contained within the UTP and STP cable. Such corrosion would diminish the efficient functioning of the network.

4. Why should fluorescent lighting be avoided in a wiring closet?

Lighting requirements for a telecommunications closet specify a minimum of 500 lx (brightness of light equal to 50-foot candles) and specify that light fixtures be mounted a minimum of 2.6 meters above the floor.

5. What types of devices might be connected to a network?

Repeaters, hubs, bridges, switches, clients, servers, printers, and routers.

6. What is the difference between and MDF and an IDF?

A good way to start looking for a potential wiring closet location is to identify secure locations that are close to the POP. The selected location can serve as either the sole wiring closet or the MDF. The MDF acts as the central wiring closet that will connect to all remote wiring closets (IDFs) through vertical cabling.


7. Is one wiring closet adequate for a multibuilding campus?

One wiring closet is required for each building, and each floor within that building. If a campus environment has eight buildings, the absolute minimum number of wiring closets would be eight.

8. What is the difference between and normal-mode problem and a common-mode problem?

If a problem exists between the hot and neutral wire, this is referred to as a normal-mode problem. If a situation involves either the hot or neutral wire and the safety ground wire, it is referred to as a common-mode problem.

9. Why is a common-mode problem more serious than a normal-mode problem?

Normal-mode problems do not ordinarily pose a hazard to you or to your computer. This is because they are usually intercepted by a computers power supply, an uninterruptible power supply, or an AC power-line filter. Common-mode problems, on the other hand, can go directly to a computers chassis without an intervening filter. Therefore, they can do more damage to data signals than normal-mode problems.

10. What is a surge?

A surge is any voltage increase above 110 percent of the normal voltage carried by a power line.

11. What is a sag?

A sag is any decrease of below 80 percent in the normal voltage carried by a power line. A sag is sometimes referred to as a brownout.

12. What is a spike?

A spike is any power impulse lasting between .5 and 100 microseconds and possessing an amplitude over 100 percent of peak power-line voltage.



The following questions help you pass the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: First-Year Companion Guide, Second Edition.

1. Which of the following does not describe a wiring closet?

a. Room used for housing the wiring for a voice network b. Room used for housing the wiring for a data network c. Room at the center of a Token Ring topology d. Room at the center point of a star topology

2. Which of the following equipment is not typically found in a wiring closet?

a. Telecommunications outlets b. Patch panels c. Wiring hubs d. Routers

3. What is a wiring closet?

a. Room where electrical power enters a commercial building b. Room used for housing the wiring for a data or voice network c. Room at the center of a Token Ring network d. Room where the entire power supply to a commercial building can be

controlled

4. In a large network, what is a wiring closet that other wiring closets are dependent upon called?

a. Master wiring facility (MWF) b. Master star topology (MST) c. Main distribution facility (MDF) d. Extended star topology (EST)


5. What is the difference between a main distribution facility (MDF) and intermediate distribution facility (IDF)?

a. The MDF contains the primary network server and the major network devices; whereas, the IDFs contain only the necessary additional routers and repeaters.

b. The MDF is on the lowest floor in a multifloor network; whereas, the IDFs are on upper floors.

c. The MDF has all the bridges, hubs, routers, and ports needed for the network; whereas, the IDFs hold any needed repeaters.

d. The MDF is the primary communications room and the central point in the network; whereas, the IDFs are secondary communications rooms dependent upon the MDF.

6. Which of the following is not a feature of a network with more than one wiring closet?

a. Dependent star topologies b. An MDF c. An IDF d. An extended star topology

7. What type of network topology usually has more than one wiring closet?

a. Token Ring b. Extended star c. Tree d. Bus

8. Which of the following best describes a type of connection made at the LAN patch panel?

a. Network device ports connect directly to patch panel pins. b. Horizontal cabling runs connect directly to the horizontal cross-connect. c. Horizontal cabling runs connect directly to telecommunications outlets. d. Patch cords connect the horizontal cross-connect directly to the patch

panel.


9. Which of the following is not a type of connection made at the LAN patch panel?

a. Patch cords interconnect computers and hubs. b. Patch cords directly connect devices to telecommunications ports. c. Horizontal cabling runs are terminated at the patch panel. d. Patch cords connect the horizontal cross-connect directly to the patch

panel.


Chapter 9

Structured Cabling Project

Introduction

After the decision is made to network computers in a building, one of the first things you must address is where the wiring closet will be located. To determine where the wiring closet will be located, it will help to think of the hub as the center point of a circle with lines of horizontal cabling radiating out from it like spokes from the center of a wheel. Then, locate all the devices that will be connected to the network on a floor plan of the building that is drawn approximately to scale. As you do this, remember that computers will not be the only devices you will want to connect to the network. You also must consider the location of printers and file servers that will be part of the network. When you connect cable to jacks, remember to strip back only as much of the cables jacket as is required to terminate the wires. The more wire that is exposed, the poorer the connection is. This exposure results in signal loss. In addition, maintain the twists in each pair of wires as close as possible to the point of termination. It is the twisting of the wires that produces cancellation, which is needed to prevent radio and electromagnetic interference. For Category 4 UTP, the maximum amount of untwisting that is allowed is 1 inch. For Category 5 UTP, the maximum amount of untwisting that is allowed is ½ inch. If multiple cables are run over the same path, use cable ties to cinch them together. When cable ties are needed to mount or secure cable, be sure to apply cable ties so they can slide a little. Position ties at random intervals along the cable. Never secure the cable ties too tightly; such tightness can damage the cable. When securing the cable ties, try to minimize the amount of jacket twisting. If cable is twisted too much, it can lead to torn cable jackets. Never allow the cable to be pinched or kinked. If this occurs, data moves more slowly and your LAN operates at less than optimal capacity. When handling the cable, avoid stretching it. If you exceed 25 pounds of pull, wires inside the cable can untwist. As you have learned, if wire pairs become untwisted, this can lead to interference and crosstalk. Above all, never cut corners with cable. It is important to leave ample slack. Remember, a few feet of extra cable is a small price to pay to avoid having to redo a cable run because of mistakes resulting in stretched cable. Most cable installers avoid this problem by leaving enough slack so that the cable can reach the floor and extend another two or three feet at both ends of the cable. Other installers follow the practice of leaving a service coil, which is nothing more than a few extra feet of cable left coiled up inside the ceiling or in another out-of-the-way location. Use appropriate and recommended techniques for dressing and securing the cable. These include cable ties, cable support bars, wire management panels, and releasable Velcro straps. Never use a staple gun to position cables. Staples can pierce the jacket, which results in loss of connection.


Concept Questions


• Generally speaking, the wiring closet must be large enough to accommodate the equipment and wiring located in it. How do you determine how large the closet should be? TIA/EIA-568-A specifies that, in an Ethernet LAN, the horizontal cabling runs must be attached to a central point in a star topology. The central point is the wiring closet, where the patch panel and the hub must be installed. The wiring closet must be large enough to accommodate all of the equipment and wiring that will be placed in it and account for future growth. Naturally, the size of the closet will vary with the size of the LAN and the types of equipment required to operate it. Equipment required for some small LANs might take up as little space as a large filing cabinet; whereas, a large LAN could require a full-fledged computer room.

• The wiring closet must be large enough to accommodate future growth. How do you estimate the future growth of a network? Attempt to estimate how many future network segments and remote LAN segments will need to be attached in the future. Is there any plan to expand into a multiple floor building? Are there any merger or acquisitions plans for the future?

• EIA/TIA-569 specifies that there be a minimum of one wiring closet per floor and states that additional wiring closets should be provided for each area up to 1000 square meters when the floor area served exceeds 1000 square meters or the horizontal cabling distance exceeds 90 meters. Hint: 1000 square meters equals 10,000 square feet; 90 meters equals approximately 300 feet.

• Anytime you install cable, it is important to document what you have done. Therefore, as you install cable, be sure to make a cut sheet. A cut sheet is a rough diagram that shows where cable runs are. It also indicates what the numbers of the schoolrooms, offices, or other rooms are where the cable runs lead to. Draw and document the cabling for a small LAN. Include three terminals in three different rooms and provide for Internet access. Students should sketch a small diagram using the correct symbols representing each LAN/WAN device. Look for horizontal cabling, patch panels, keystone jacks Later, you can refer to this cut sheet so that corresponding numbers can be placed on all telecommunications outlets and at the patch panel in the wiring closet. You can use a page in your journal to document cable runs. By placing it in your journal, you have an additional layer of documentation for any cable installation.


• EIA/TIA-606 specifies that some kind of unique identifier must be given to each hardware termination unit. This identifier must be marked on each termination hardware unit or on its label. When identifiers are used at the work area, station terminations must be labeled on the faceplate housing, or on the connector itself. Whether they are adhesive or insertable, all labels must meet legibility, defacement, and adhesion requirements. Label the drawing that you did earlier in this exercise with the identifier to each hardware termination unit. Students should now provide details to the diagram that they had sketched. Termination endpoints include patch panels and keystone jacks.


Define the following terms as completely as you can. Use the online Chapter 9 or the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition, material for help. Algorithm Well-defined rule or process for arriving at a solution to a problem. In networking, algorithms are commonly used to determine the best route for traffic from a particular source to a particular destination.

Backbone The part of a network that acts as the primary path for traffic that is most often sourced from, and destined for, other networks.

Backoff The retransmission delay enforced when a collision occurs.

Bus Common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another. Sometimes called highway.

Bus topology Linear LAN architecture in which transmissions from network stations propagate the length of the medium and are received by all other stations.

Catchment Zone that falls within area that can be served by an internetworking device such as a hub.

Collision In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and are damaged when they meet on the physical media.

Collision domain In Ethernet, the network area within which frames that have collided are propagated. Repeaters and hubs propagate collisions; LAN switches, bridges, and routers do not. Cut sheet A rough diagram indicating where cable runs are located and the numbers of rooms they lead to.

EIA-TIA-606 Administration standard for the telecommunications infrastructure of commercial buildings. It includes the following administration areas: terminations, media, pathways, spaces, and bounding and grounding.

Fish tape Retractable coil of steel tape used to guide cable through a wall from above or below.

Gutter Type of wall-mounted channel with removable cover used to support horizontal cabling. Gutter is big enough to hold several cables.


Hammer drill Tool resembling an oversized electric drill used for drilling into masonry. As it turns the bit, it hammers rapidly.

HCC (horizontal cross-connect) Wiring closet where the horizontal cabling connects to a patch panel which is connected by backbone cabling to the main distribution facility.

Hierarchical star topology Extended star topology where a central hub is connected by vertical cabling to other hubs that are dependent on it.

Highway Common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another. See Bus.

ICC IDF that connects the horizontal cross-connect to the main cross-connect.

IDF (intermediate distribution facility) Secondary communications room for a building using a star networking topology. The IDF is dependent on the MDF.

MCC (main cross-connect) Wiring closet that serves as the most central point in a star topology and where LAN backbone cabling connects to the Internet.

MDF (main distribution facility) Primary communications room for a building. Central point of a star networking topology where patch panels, hub, and router are located.

Noise Undesirable communications channel signals.

Patch panels An assembly of pin locations and ports that can be mounted on a rack or wall bracket in the wiring closet. Patch panels act like switchboards, connecting workstations cables to each other and to the outside.

Pin locations A color-coded slot on a patch panel. Cable wires are punched down using a punch tool to make an electrical connection that allows the network to function.

POP (Point of Presence) Point of Presence is the point of interconnection between the communication facilities provided by the telephone company and the building's main distribution facility.

Ports 1) Interface on an internetworking device (such as a router). 2) In IP terminology, an upper-layer process that is receiving information from lower layers. 3) To rewrite software or microcode so that it will run on a different hardware platform or in a different software environment than that for which it was originally designed. 4) A female plug on a patch panel that accepts the same size plug as an RJ-45 jack. Patch cords are used in these ports to cross connect computers wired to the patch panel. This cross connection allows the LAN to function.

Pull string Strong, heavy string used to pull cable in multiple runs.

Punch-down tool Spring-loaded tool used for cutting and connecting wire in a jack or on a patch panel. Raceway Wall-mounted channel with a removable cover used to support horizontal cabling.

RJ connector (registered jack connector) Standard connectors originally used to connect telephone lines. RJ connectors are now used for telephone connections and for 10BaseT and other types of network connections. RJ-11, RJ-12, and RJ-45 are popular types of RJ connectors.


Signal injector Device used to measure attenuation of a signal on a network.

Star topology LAN topology in which endpoints on a network are connected to a common central switch by point-to-point links. A ring topology that is organized as a star implements a unidirectional closed-loop star, rather than point-to-point links.

Telepole Telescoping pole with a hook at one end. It is used to get cable across a ceiling or attic quickly.

Tie wraps Plastic ties used for holding cables together or for holding cables in place.

Wire maps Feature provided by most cable testers. Used to test twisted-pair cable installations, it shows which wire pairs connect to what pins on the plugs and sockets.

Focus Questions

1. Where are patch cables plugged into?

Patch cords connect to patch panel ports, making it possible to interconnect computers and other network devices (such as hubs, repeaters, and routers).

2. Think about the cabling in this building. What factors would the person laying cable have to keep in mind? How would someone keep track of all the cables?

The cable installer needs to pay attention to safety standards, sources of potential noise (motors, light fixtures, and so on), and general wiring standards identified by TIA/EIA. Whenever you install cable, it is important that you document your actions. You can do this by using a cut sheet as you install the cable. A cut sheet is a rough diagram that shows the locations of the cable runs. It also indicates the numbers of the classrooms, offices, or other rooms to which the cables have been run.

3. How do you determine whether cable has been properly installed?

The IEEE and the TIA/EIA have established standards that enable you to test whether your network is operating at an acceptable level. If your network passes this test and is certified as meeting the standards, you can use this measurement as an established baseline. The baseline is a record of your networks starting point or newly installed performance capabilities.

4. What do you call an assembly of pin locations and ports that can be mounted on a rack?

A patch panel. Found in both the MDF and IDF.


5. What type of vertical cabling connects the central hub to other hubs in a hierarchical star topology?

Vertical cabling usually consists of single or multimode fiber. If the central hub and other hubs are within 90 meters and on the same floor and earth ground, then Cat 5 or Cat 5e is also a suitable choice.

6. What type of tool is used to measure attenuation of a signal on a network?

A cable tester can measure the reduction in power of a signal received from a device known as a signal injector, a small box approximately the size of a deck of playing cards that is attached to the far end of a cable. Cable testers generally measure attenuation at several frequencies.




1. Which of the following statements best describes the EIA/TIA-569 specification for wiring closets?

a. There should be a minimum of one wiring closet for every floor of a building.

b. There should be a maximum of one wiring closet for every floor of a building.

c. There should be a minimum of two wiring closets for every floor of a building.

d. There should be a maximum of two wiring closets for every floor of a building.

2. Which of the following best describes the EIA/TIA-569 standard for additional wiring closets?

a. Additional wiring closets should be provided for each area up to 90 square meters when the floor area served exceeds 90 square meters or the horizontal cabling distance exceeds 90 meters.

b. Additional wiring closets should be provided for each area up to 100 square meters when the floor area served exceeds 100 square meters or the horizontal cabling distance exceeds 9 meters.

c. Additional wiring closets should be provided for each area up to 1000 square meters when the floor area served exceeds 1000 square meters or the horizontal cabling distance exceeds 30 meters.

d. Additional wiring closets should be provided for each area up to 1000 square meters when the floor area served exceeds 1000 square meters or the horizontal cabling distance exceeds 90 meters.

3. If Acme Inc. occupies 3500 square meters on the second floor of a building, how many wiring closets should be installed according to EIA/TIA 569?

a. One b. Two c. Three d. Four


4. If Acme Inc. occupies the first three floors of a building and each floor is 1500 square meters, how many wiring closets should be installed according to EIA/TIA 569?

a. One b. Three c. Six d. Nine

5. Which of the following is not a specification for walls, floors, and ceilings of a wiring closet?

a. A minimum of 15 feet of wall space should be provided for terminations and related equipment for the POP.

b. Rooms selected for wiring closets should have a dropped or false ceiling for easy access.

c. Interior walls on which equipment is to be mounted should be covered with ¾" plywood that is raised away from the underlying wall a minimum of 1 ¾".

d. Floor coverings should be tile or other type of finished surface to help control dust.

6. What is a Point of Presence (POP)?

a. The point where the horizontal cabling connects to the backbone b. The point where the electrical power lines enter the building c. The point where the telephone companys equipment and the buildings

main distribution facility connect d. The point where the network and the electrical system of the building

connect

7. Why should wiring closets not have a dropped or false ceiling?

a. The minimum ceiling height specified by EIA/TIA-569 cannot be met in most rooms with most dropped or false ceilings.

b. The temperature and humidity cannot be adequately controlled. c. Dust from the ceiling materials poses a problem for long-term equipment

maintenance. d. Access is not controlled because people can get into the room through

the ceiling.


8. What kind of floor should the wiring room have?

a. Tile or other finished surface b. Carpet c. Unfinished stone d. Electronics grade carpet

9. What is the minimum and maximum relative humidity level that should be maintained for rooms serving as wiring closets?

a. Between 10 percent and 50 percent b. Between 20 percent and 70 percent c. Between 30 percent and 50 percent d. Between 30 percent and 70 percent

10. What should the approximate temperature in a wiring closet be when all LAN equipment is fully functioning? a. 60 degrees Fahrenheit b. 65 degrees Fahrenheit c. 70 degrees Fahrenheit d. 75 degrees Fahrenheit

11. Which of the following is not a requirement for lighting fixtures or power outlets in a wiring closet?

a. Fluorescent lighting is recommended to avoid outside interference. b. A wall switch to turn room lighting on and off should be located

immediately inside the door. c. At least one duplex power outlet should be located every 1.8 meters or 10

feet along each wall in a main distribution facility. d. At least two duplex power outlets should be located along each wall if the

wiring closet is to serve as an intermediate distribution facility.

12. Why should fluorescent light fixtures be avoided in wiring closets?

a. They provide false color lighting, which can lead to mistakes in making connections.

b. They generate outside electrical interference. c. They can degrade some plastic materials used in network equipment. d. There often is insufficient room in a wiring closet to change out the

fluorescent bulbs easily and safely.


13. Which of the following is not a requirement for room and equipment access in a wiring closet?

a. The door should be at least three feet wide and should swing open out of the room to ensure easy access to the room for workers and equipment.

b. The wiring closet should lock from an outside access in such a way that exiting from the room is always possible.

c. Wiring hubs and patch panels may be wall-mounted using hinged wall brackets that are attached to the plywood covering the underlying wall surface.

d. When a distribution rack is used to mount patch panels and wiring hubs, the minimum distance for the rack from the wall should be six inches.

14. Which of the following is not a wiring closet specification for cable access and support?

a. Access to the wiring closet for all horizontal cabling coming from the work areas should be via a raised floor.

b. All cable leaving the room to intermediate distribution facilities and computer and communications rooms located on other floors of a building should be via four-inch conduits or sleeved cores.

c. One excess sleeved core or conduit should be provided in each wiring closet to provide for future anticipated growth.

d. Any wall or ceiling openings provided for conduits or sleeved cores must be sealed with smoke and flame retardant materials.

15. What is the first step in locating a wiring closet for a network?

a. Identify the number of computers that will be part of the network. b. Identify the number of printers and file servers that will be part of the

network. c. Identify all devices that will be connected to the network on a floor plan. d. Identify the topological requirements of devices that will be in the

network.

16. Which of the following would not be considered when selecting a potential location for a wiring closet?

a. Identify a secure location close to the POP. b. Determine the exact number of wiring closets needed for the network. c. Determine the location of the buildings communication facilities. d. Make an initial selection of potential locations based on EIA/TIA-569

specifications.


17. What is the name for the most centrally located wiring closet in a LAN with an extended star typology?

a. Catchment area b. Main distribution facility c. Intermediate distribution facility d. Repeated distribution facility

18. Where should the main distribution facility (MDF) be located if a LAN with an extended star topology is used in a multistory building?

a. Next to the POP b. On the first floor c. On one of the middle floors d. In the basement

19. Where should a repeater be located in a LAN with an extended star topology?

a. Catchment area b. Main distribution facility c. Intermediate distribution facility d. Repeated distribution facility

20. What network device is used in an extended star topology when the catchment area of one wiring closet is not enough?

a. Repeater b. Backoff c. Terminator d. Suppressor

21. What type of cabling provides interconnections between wiring closets and the POP, and between buildings that are part of the same LAN?

a. Token Ring cabling b. Backbone cabling c. Coaxial cabling d. Horizontal cabling


22. What type of cabling is used to connect the POP to the MDF when an Ethernet LAN is in a multistory building?

a. Backbone cabling b. Coaxial cabling c. Horizontal cabling d. Token Ring cabling

23. What type of cabling is used to connect an MDF to IDFs when an Ethernet LAN is in a multistory building?

a. Token Ring cabling b. Backbone cabling c. Coaxial cabling d. Horizontal cabling

24. What type of cabling is used to connect IDFs on each floor to the various work areas when an Ethernet LAN is in a multistory building?

a. Backbone cabling b. Coaxial cabling c. Horizontal cabling d. Token Ring cabling

25. Which type of networking media is installed most often for backbone cabling?

a. 100-ohm unshielded twisted-pair cable b. 150-ohm shielded twisted-pair cable c. 62.5/125-micron fiber-optic cable d. 50-ohm coaxial cable

26. Which of the following types of networking media is not recommended for backbone cabling?

a. 100-ohm unshielded twisted-pair cable b. 150-ohm shielded twisted-pair cable c. 62.5/125-micron fiber-optic cable d. 50-ohm coaxial cable


27. What kind of connection is used in a wiring closet where the horizontal cabling connects to a patch panel that is connected by backbone cabling to the main distribution facility?

a. Horizontal cross-connect b. Vertical cross-connect c. Intermediate cross-connect d. Main cross-connect

28. What kind of connection is used in a wiring closet that serves as the most central point in a star topology and where LAN backbone cabling connects to the Internet?


29. What kind of connection is used in an IDF that connects the horizontal cross-connect to the main cross-connect?


30. What is the maximum distance for backbone cabling if single-mode, fiber-optic cable is used to connect the horizontal cross-connect to the main cross-connect?

a. 500 meters b. 1000 meters c. 2500 meters d. 3000 meters

31. What is the maximum distance for backbone cabling if single-mode, fiber-optic cable is used to connect the intermediate cross-connect to the main cross-connect?



32. What is the maximum distance for backbone cabling if single-mode, fiber-optic cable is used to connect the horizontal cross-connect to the intermediate cross-connect?



Chapter 10

Layer 3: Routing and Addressing

Introduction

The network layer interfaces to networks and provides the best end-to-end packet delivery services to its user, the transport layer. The network layer sends packets from the source network to the destination network. Routers are devices that implement the network service. They provide interfaces for a wide range of links and subnetworks at a wide range of speeds. Routers are active and intelligent network nodes and thus can participate in managing the network. Routers manage networks by providing dynamic control over resources and supporting the tasks and goals for networks: connectivity, reliable performance, management control, and flexibility. In addition to the basic switching and routing functions, routers have implemented a variety of value-added features that help to improve the cost-effectiveness of the network. These features include sequencing traffic based on priority and traffic filtering. Typically, routers are required to support multiprotocol stacks, each with its own routing protocols, and to allow these different environments to operate in parallel. In practice, routers also incorporate bridging functions and can serve as a limited form of hub. IP addressing makes it possible for data passing over the network media of the Internet to find its destination. Because each IP address is a 32-bit value, there are four billion different IP address possibilities. IP addresses are hierarchical addresses, like phone numbers and zip codes. They provide a better way to organize computer addresses than MAC addresses, which are flat addresses (like social security numbers). IP addresses can be set in software and are therefore flexible. MAC addresses are burned into hardware. Both addressing schemes are important for efficient communications between computers.

Concept Questions


• Path determination occurs at the network layer. Routers are another type of internetworking device. These devices pass data packets between networks based on network protocol or Layer 3 information. Explain how this process works. Routers use logical addressing to made routing decisions. When a packet is received by a router, it pulls of Layer 2 frame encapsulation and analyses the Layer 3 header. It uses this destination address along with its routing table to determine the best path and ultimately the next hop.


• Routers have the capability to make intelligent decisions as to the best path for delivery of data on the network. What criteria do they use to make these decisions? Routers share information with other routers, educating one another about known networks within the internetwork. The router uses this table, almost like a network roadmap. When requested to forward a packet, the router refers to this map/table and forwards the packet to the next appropriate interface and neighbor.

• IP addresses are 32-bit values written as four octets separated with periods. To make them easier to remember, IP addresses are usually written in dotted notation using decimal numbers. IP addresses are used to identify a machine on a network and the network to which it is attached. What do each of the numbers mean? Dotted-decimal notation allows for easier identification of the IP address. Each decimal number (octet) represents 8 individual bits. Those bits are used to represent either the host or network portion of this unique address. The subnet mask actually indicates whether the bit is representative of the host or network.

Hexadecimal is a Base 16 numbering system that is used to represent MAC addresses. It is referred to as Base 16 because it uses 16 symbols; combinations of these symbols can then represent all possible numbers. Because only 10 symbols represent digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), and Base 16 requires 6 more symbols, the extra symbols are the letters A, B, C, D, E, and F. The position of each symbol, or digit, in a hex number represents the base number 16 raised to a power, or exponent, based on its position. Moving from right to left, the first position represents 160, or 1; the second position represents 161, or 16; the third position, 162, or 256; and so on. Example: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 0 1 2 3 4 5 6 7 8 9 A B C D E F 4F6A = (4 x 163) + (F[15] x 162) + (6 x 161) + (A[10] x 160)

Convert Decimal to Hex

Converting from decimal to binary is done with a procedure called the remainder method. This method uses successive divisions of the base number of the system. You can use the same method to convert decimal into hex, or Base 16. Example: 24,032 / 16 = 16 into 24,032 is 1502, with a remainder of 0 1502 / 16 = 16 into 1502 is 93, with a remainder of 14, or E 93 / 16 = 16 into 93 is 5, with a remainder of 13, or D 13 / 16 = 16 into 13 is 0, with a remainder of 3 Collecting all the remainders backward returns the hex number 3DE0.


Convert These Decimal Numbers to Binary:

32,014 Hex number = 7D0E 56,432 Hex number = DC70 57,845 Hex number = E1F5 98,764 Hex number = 181CC 54,462 Hex number = D4BE

Convert Hex to Decimal

Convert hexadecimal numbers to decimal numbers by multiplying the hex digits by the base number of the system, in this case, Base 16, raised to the exponent of the position. Example: Convert the hex number 3F4B to decimal. (Work from right to left.) B x 163 = 12,288 F(15) x 162 = 3840

4 x 161 = 64 B(11) x 160 = 11

16,203 = Decimal equivalent

Convert These Hex Numbers to Decimal:

23F6 Decimal = 9206 6AB7 Decimal = 27,319 5FE3 Decimal = 24,547 87CE Decimal = 34,766 59AC Decimal = 22,956




Segment 1) Section of a network that is bounded by bridges, routers, or switches. 2) In a LAN using a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters. 3) Term used in the TCP specification to describe a single transport layer unit of information. Internet service providers (ISPs) Companies that offer services that tie together multiple network segments.


Address Data structure or logical convention used to identify a unique entity, such as a particular process or network device. IP (Internet Protocol) Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Documented in RFC 791.

Broadcast address Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all 1s. Subnetwork In IP networks, a network sharing a particular subnet address. Subnetworks are networks arbitrarily segmented by a network administrator to provide a multilevel, hierarchical routing structure while shielding the subnetwork from the addressing complexity of attached networks. Sometimes called a subnet. Subnet mask A 32-bit address mask used in IP to indicate the bits of an IP address that are being used for the subnet address. Sometimes referred to simply as mask.

Focus Questions

1. What type of addressing scheme does the network layer address use?

Logical addressing occurs at the network layer. The network layer address has both network and host representation; because of this, Layer 3 addresses are said to be hierarchical.

2. The Internet is a collection of network segments that are tied together to facilitate the sharing of information. What specific internetworking device that operates at Layer 3 interconnects networks?

Routers allow for the interconnection of several unique segments.


3. What type of determination is the process the router uses to choose a course for the packet to travel to its destination?

Path determination is the process that a router uses to choose the next hop in a path toward a packets ultimate destination.

4. At what layer does addressing occur?

A network address helps the router identify a path within the network cloud. The router uses the network address to identify the destination network of a packet within an internetwork. In addition to the network address, network protocols use some form of host, or node, address. For some network layer protocols, a network administrator assigns host addresses according to some predetermined network addressing plan.

5. When a computer is moved to a different network, what type of address remains the same and what type of address must be reassigned?

When you physically move a computer to a different network, the computer maintains the same MAC address, but you must assign it a new network layer address.

6. What is the difference between a flat addressing scheme and a hierarchical addressing scheme?

Protocols that support the network layer use a hierarchical addressing scheme that allows for unique addresses across network boundaries, along with a method for finding a path for data to travel between networks. MAC addresses use a flat addressing scheme that makes it difficult to locate devices on other networks. Hierarchical addressing, on the other hand, not only enables information flow through an internetwork, but it also provides an efficient means of doing so. Flat addressing does not allow for the grouping of multiple devices based upon some common characteristic, such as department, floor, company, city, and so on.

7. In the IP header, what information does the “total length” contain?

Specifies the length of the entire IP packet, including data and header, in two bytes (16 bits).

8. What three pieces of information does the subnet mask give to network devices?

The subnet mask allows the host to identify the size of the network on which it is participating. The subnet mask also allows for the identification of a network address (all 0s in the Host field) and the identification of the broadcast address (all 1s in the Host field).

9. How many hosts can be assigned to a Class C network?

A Class C network contains 256 host addresses. The first (.0) and the last (.255) are reserved, leaving 254 host IP addresses available for assignment.



The following questions help you review for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which layer of the OSI model uses the Internet Protocol addressing scheme to determine the best way to move data from one place to another?


2. What function allows routers to evaluate available routes to a destination and to establish the preferred handling of a packet?

a. Data linkage b. Path determination c. SDLC interface protocol d. Frame Relay

3. IP addresses are necessary for which of the following reasons?

a. To identify a machine on a network and the network to which it is attached

b. To identify a machine on a network c. To identify the network d. To keep track of whom is on a network

4. Which of the following best describes a network address on the Internet?

a. All four octets in the address are different. b. Each address is unique. c. The first three octets can be the same, but the last one must be different. d. Two of the four octets can be the same, but the other two have to be

different.

5. Who assigns the network portion of every IP address?

a. The local network administrator b. The person who owns the computer c. The Network Information Center d. The host network administrator


6. The network number plays what part in an IP address?

a. Specifies the network to which the host belongs b. Specifies the identity of the computer on the network c. Specifies which node on the subnetwork is being addressed d. Specifies which networks the device can communicate with

7. The host number plays what part in an IP address?

a. Designates the identity of the computer on the network b. Designates which node on the subnetwork is being addressed c. Designates the network to which the host belongs d. Designates which hosts the device can communicate with

8. A Class A address is given to what sort of organization?

a. An individual b. A medium-size company c. A large corporation d. A government

9. In a Class A address, how many of the octets are assigned by InterNIC?

a. The first octet is assigned by NIC. b. The first and second octet are assigned by NIC. c. The first, second, and third octets are assigned by NIC. d. All the octets are assigned by InterNIC.

10. In a Class A address, the value of the first octet can equal which of the following?

a. The value of first octet is 0 through 127. b. The value of first octet is 128 through 191. c. The value of first octet is 192 through 223. d. The value of first octet is 192 through 255.

11. A Class B address is given to what sort of organization?

a. An individual b. A medium-size company c. A large corporation d. A government


12. In a Class B address, how many of the octets are assigned locally?

a. The first octet is assigned locally. b. The second octet is assigned locally. c. The second and third octets are assigned locally. d. The third and fourth octets are assigned locally.

13. The following address is of which class? 129.21.89.76

a. Class A b. Class B c. Class C d. Address not valid

14. A Class C address is given to what sort of organization

a. An individual b. A medium-size company c. A huge corporation d. A government e. This address space was intended to support a small network.

15. Which of the following addresses is a Class C address?

a. 129.219.95.193 b. 209.101.218.30 c. 151.13.27.38 d. 192.119.15.17


Chapter 11

Layer 3: Protocols

Introduction

Protocols determine whether data is passed beyond the network layer to higher levels of the OSI model. Basically, for this to occur, the data packet must contain both a destination MAC address and a destination IP address. If it lacks one or the other, the data does not pass to the upper levels. In this way, MAC addresses and IP addresses act as a sort of check and balance for each other.

Concept Questions


• If the destination is to retain the data and pass it along to the upper layers of the OSI model, the source must use both a destination MAC address and a destination IP address. Therefore, the device initiates a process called an ARP request that is designed to help it discover what the destination MAC address is. How does the device know to initiate the ARP request? Whenever a network device wants to send data across a network, it uses information provided by its ARP table. If it is cannot locate a MAC address for the destination IP address in its ARP table, the host initiates a process called an ARP request.

• The protocol that a device uses when it does not know its own IP address is the Reverse Address Resolution Protocol (RARP). Like ARP, RARP binds MAC addresses to IP addresses so that network devices can use them to encapsulate data before sending it out on the network. Can you explain how this works? RARP binds MAC addresses to IP addresses. This binding allows network devices to encapsulate data before sending them out on the network. A network device, such as a diskless workstation, might know its MAC address but not its IP address. Devices using RARP require that a RARP server be present on the network to answer RARP requests.



ARP (Address Resolution Protocol) Internet protocol used to map an IP address to a MAC address. Defined in RFC 826. Compare with RARP. See also proxy ARP.


BOOTP Protocol used by a network node to determine the IP address of its Ethernet interfaces, in order to affect network booting.

Connection oriented Term used to describe data transfer that requires the establishment of a virtual circuit. See also connectionless. See also virtual circuit.

Connectionless Term used to describe data transfer without the existence of a virtual circuit. Compare with connection oriented. See also virtual circuit.

Datagram routing Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit. IP datagrams are the primary information units in the Internet. The terms cell, frame, message, packet, and segment are also used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.

Dynamic address resolution Use of an address resolution protocol to determine and store address information on demand Enhanced IGRP (EIGRP) Advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance-vector protocols. Compare with IGRP. See also IGP, OSPF, and RIP.

ICMP (Internet Control Message Protocol) Network layer Internet protocol that reports errors and provides other information relevant to IP packet processing. Documented in RFC 792.

IP (Internet Protocol) Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Documented in RFC 791.

IP address 1) A 32-bit address assigned to hosts using TCP/IP. An IP address belongs to one of five classes (A, B, C, D, or E) and is written as 4 octets separated with periods (dotted-decimal format). Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing; whereas, the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. Also called an Internet address. 2) Command used to establish the logical network address of this interface. See also IP and subnet mask.

RARP (Reverse Address Resolution Protocol) Protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses. Compare with ARP.

Routed protocol Protocol that can be routed by a router. A router must be able to interpret the logical internetwork as specified by that routed protocol. Examples of routed protocols include AppleTalk, DECnet, and IP.

Router Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information. Occasionally called a gateway (although this definition of gateway is becoming increasingly outdated). Compare with gateway.


Routing protocol Protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols include IGRP, OSPF, and RIP.

TCP (Transmission Control Protocol) Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack.

TCP/IP (Transmission Control Protocol/Internet Protocol) Common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of worldwide internetworks. TCP and IP are the two best-known protocols in the suite. See also IP and TCP.

Focus Questions

1. What are the two addressing schemes in networking?

In networking there are two addressing schemes: One uses the MAC address, a data link or Layer 2 address; the other uses an address located at the network layer, or Layer 3 of the OSI model.

2. When making forwarding decisions, what type of addresses do routers use?

Routers use a Layer 3 addressing scheme make forwarding decisions. They use IP or logical addresses rather than MAC addresses.

3. A router’s attachment to a network is called an interface, which can also be referred to as what?

A routers attachment to a network is called an interface; it also may be referred to as a port. In IP routing, each interface must have a separate, unique network (or subnetwork) address.

4. What protocol does a device use to obtain an IP address when it starts up?

A device uses BOOTstrap Protocol, when it starts up, to obtain an IP address. BOOTP uses UDP to carry messages; the UDP message is encapsulated in an IP datagram.

5. When devices communicate, what suite is used to automatically detect the MAC address?

For devices to communicate, the sending devices need both the IP addresses and the MAC addresses of the destination devices. When they try to communicate with devices whose IP addresses they know, they must determine the MAC addresses. The TCP/IP suite has a protocol that can automatically detect the MAC address (ARP). ARP enables a computer to find the MAC address of the computer that is associated with an IP address.


6. When a router receives a frame, what happens to the frame header and the IP header?

At the data link layer, an IP datagram is encapsulated into a frame. The datagram, including the IP header, is treated as data. A router receives the frame, strips off the frame header, and then checks the destination IP address in the IP header.

7. Do most network services use connectionless or connection-oriented delivery systems?

Most network services use a connectionless delivery system. They treat each packet separately, and send it on its way through the network. The packets may take different paths to get through the network, but are reassembled when they arrive at the destination. In a connectionless system, the destination is not contacted before a packet is sent. In connection-oriented systems, a connection is established between the sender and the recipient before any data is transferred. An example of a connection-oriented network is the telephone system. A call is placed, a connection is established, and then communication occurs.

8. What is the difference between EIGRP and IGRP?

EIGRP is an advanced version of IGRP. Specifically, EIGRP provides superior operating efficiency and combines the advantages of link-state protocols with those of distance-vector protocols. When a source resides on a network that has a different network number than that of the desired destination, and when it does not know the MAC address of the destination, it must use the services of a router, for its data to reach the destination. A router that is used for this purpose is called a default gateway.

9. What is the most common method to transfer routing protocols between routers on the same network?

The most common method, within a network, to transfer routing information between routers that are located on the same network, is RIP.



The following questions help you review for the CCNA exam. Answers also appear in Appendix A, Answers to the CCNA Exam Review Questions, from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I , Second Edition.

1. What is the Address Resolution Protocol (ARP)?

a. Network protocol used to resolve device conflicts b. Internet protocol used to map an IP address to a MAC address c. Network protocol used to identify the location of unauthorized users d. Internet protocol used to uniquely identify a user on a specific network

2. What must a data packet contain to be passed from the network layer to upper levels of the OSI model?

a. A destination MAC address and a source IP address b. A destination MAC address and a destination IP address c. A destination IP address or a source MAC address d. Either a destination IP address or a destination MAC address

3. What happens if a data packet lacks a destination IP?

a. The data packet is sent to the RARP server that traces the data packet back to its source.

b. The MAC address takes priority and the data packet is passed up to the next network layer.

c. The ARP tables will be consulted to resolve any conflict. d. Data packets will not be passed to the next higher network layer.

4. What happens if a data packet lacks a MAC address?

a. The data packet is sent to the RARP server that traces the data packet back to its source.

b. The IP address takes priority and the data packet is passed up to the next higher network layer.

c. The ARP tables will be consulted to resolve any conflict. d. Data packets will not be passed to the next higher network layer.


5. What happens if the ARP table maps the destination IP address to the destination MAC address?

a. The data packet is sent to the RARP server. b. The source broadcasts the IP address to all devices. c. The IP address is bound with the MAC address. d. The network traffic is reduced and response times decreased.

6. What initiates an ARP request?

a. A device is unable to locate the destination IP address in its ARP table. b. The RARP server in response to a malfunctioning device. c. A diskless workstation with an empty cache. d. A device is unable to locate the destination MAC address in its ARP

table.

7. What happens if a device is unable to locate the destination MAC address in its ARP table?

a. An ARP request is sent. b. The RARP server is consulted. c. The destination IP address is used instead. d. A data packet is sent to the dummy terminal.

8. What is a header?

a. IP address of the source device placed at the beginning of the data packet

b. Route the data packet takes through the network when it follows a predetermined path

c. Control information placed before data when encapsulating that data for network transmission

d. Protocol to convert information from one stack to another at the application layer

9. What is a frame?

a. Logical grouping of information sent as a data link layer unit over a transmission medium

b. Location where ARP tables are stored on a device c. Data packet sent to a diskless workstation d. Destination MAC and IP address bound together as a data packet


10. What are the header and trailer referred to as?

a. Frame b. ARP reply c. IP address d. RARP reply

11. Which best describes the function of a frame?

a. Binding of MAC and IP addresses b. Used for synchronization and error control c. Querying of all devices on the network d. Consulting the ARP tables to look up addresses

12. What is used for synchronization and error control?

a. Trailer b. Header c. Frame d. Protocol

13. Which best describes the structure of the ARP request frame?

a. MAC and IP address b. Destination IP address and source IP address c. Frame header and ARP message d. Addresses and trailer

14. What are the two parts of the frame header called?

a. MAC header and IP header b. Source address and ARP message c. Destination address and RARP message d. Request and data packet

15. Which best describes RARP?

a. Finds MAC addresses based on IP addresses b. Calculates of shortest route between source and destination c. Finds IP addresses based on MAC addresses d. Reduces network traffic by maintaining constant contact with all network

devices


16. Why is a RARP request made?

a. A source knows its MAC address but not its IP address. b. The data packet needs to find the shortest route between destination and

source. c. The administrator needs to manually configure the system. d. A link in the network faults and a redundant system must be activated.

17. Which of the following devices build ARP tables?

a. Hubs b. Routers c. Data links d. Encoders

18. Which best defines a gateway?

a. A network device that has an IP address and maintains ARP tables b. A device that connects one network to another network c. A device that performs an application layer conversion of information

from one stack to another d. A device that cleans and amplifies signals


Chapter 12

Layer 4: The Transport Layer

Introduction

Services located in the transport layer, which is Layer 4 of the OSI reference model, enable users to segment several upper-layer applications onto the same Layer 4 data stream. These services also allow for the reassembly of the same upper-layer application segments at the receiving end. The Layer 4 data stream provides transport services from the host to the destination. Services such as these are sometimes referred to as end-to-end services. The Layer 4 data stream is a logical connection between the endpoints of a network. As the transport layer sends its data segments, it can also ensure the integrity of the data. One method of doing this is called flow control. Flow control avoids the problem of a host at one side of the connection overflowing the buffers in the host at the other side. Overflows can present serious problems because they can result in data loss. Transport-layer services also allow users to request reliable data transport between hosts and destinations. To obtain such reliable transport of data, a connection-oriented relationship is used between the communicating end systems. Reliable transport can accomplish the following:

• It ensures that segments delivered will be acknowledged back to the sender.

• It provides for retransmission of any segments that are not acknowledged.

• It puts segments back into their correct sequence at the destination.

• It provides congestion avoidance and control.

Concept Questions


• For data transfer to begin, both the sending and receiving application programs inform their respective operating systems that a connection will be initiated. How is this accomplished? One user of the transport layer must establish a connection-oriented session with its peer system. For data transfer to begin, both the sending and the receiving applications inform their respective operating systems that a connection will be initiated. One machine initiates a connection that must be accepted by the other. Protocol software modules in the two operating systems communicate by sending messages across the network to verify that the transfer is authorized and that both sides are ready.


• In concept, one machine places a call that must be accepted by the other. If the receiving machine does not accept the call, what happens? If the receiving machine does not accept the call, a session is not established. The transport of data will not be allowed to be attempted.

• Protocol software modules in the two operating systems communicate by sending messages. Messages are sent across the network to verify that the transfer is authorized and that both sides are ready. How is this accomplished? Protocol software modules in the two operating systems communicate by sending messages across the network to verify that the transfer is authorized and that both sides are ready. After all synchronization has occurred, a connection is said to be established and the transfer of data begins. During transfer, the two machines continue to communicate with their protocol software to verify that data is received correctly.

• After all synchronization occurs, a connection is established, and data transfer begins. How do both machines know that the data is flowing correctly? If the sender must wait for an acknowledgment after sending each segment, throughput is low. Therefore, most connection-oriented, reliable protocols allow more than one frame or segment to be outstanding at a time. Because time is available after the sender finishes transmitting the data packet and before the sender finishes processing any received acknowledgment, the interval is used for transmitting more data.



Best-effort delivery Describes a network system that does not use a sophisticated acknowledgment system to guarantee reliable delivery of information.

ES (end system) 1) Generally, an end-user device on a network. 2) Nonrouting host or node in an OSI network.

Flow control Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. In IBM networks, this technique is called pacing.

Full duplex Capability for simultaneous data transmission between a sending station and a receiving station. TCP (Transmission Control Protocol) Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack.


Transport layer This layer is responsible for reliable network communication between end nodes. The transport layer provides mechanisms for the establishment, maintenance, and termination of virtual circuits, transport fault detection and recovery, and information flow control.

UDP (User Datagram Protocol) Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. UDP is defined in RFC 768.

Window size Refers to the number of messages that can be transmitted while awaiting an acknowledgment.

Focus Questions

1. What type of numbers are used to keep track of different conversations that cross the network at the same time?

Both TCP and UDP use port numbers to pass information to the upper layers. Port numbers are used to keep track of different conversations that cross the network at the same time.

2. What is the name of a protocol that combines connectionless and connection-oriented service?

The Internet Protocol (IP) includes both TCP (connection-oriented) and UDP (connectionless) protocols.

3. What is the difference between TCP and UDP?

User Datagram Protocol (UDP) is the connectionless transport protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams, without acknowledgments or guaranteed delivery. Error processing and retransmission must be handled by other protocols. TCP hosts establish a connection-oriented session with one another using a three-way handshake. A three-way handshake/open connection sequence synchronizes a connection at both ends before data is transferred. This exchange of introductory sequence numbers during the connection sequence is important because it ensures that any data that is lost due to transmission problems can be recovered.

4. What is the field in a TCP segment that ensures correct sequencing of the arriving data?

TCP provides sequencing of bytes with a forward reference acknowledgment. The sequence number in the TCP header is associated with the first byte in the user data area. At the receiving station, TCP reassembles the segments into a complete message.


5. What are the protocols that use UDP?

Trivial File Transfer Protocol (TFTP) Simple Network Management Protocol (SNMP) Dynamic Host Control Protocol (DHCP) Domain Name System (DNS) BOOTP

6. What range of port numbers is reserved for public applications?

Numbers below 255 are used for public applications.

7. What type of a window refers to the fact that the window size is negotiated dynamically during the TCP session?

The sliding part of sliding window refers to the fact that the window size is negotiated dynamically during the TCP session.




1. Which layer of the OSI model provides transport services from the host to the destination?

a. Application b. Presentation c. Session d. Transport

2. Which best describes the function of the transport layer?

a. Establishes, manages, and terminates applications b. Provides transport services from the host to the destination c. Supports communication between programs like electronic mail, file

transfer, and web browsers d. Translates between different data formats such as ASCII and EBCDIC

3. Which method best describes flow control?

a. A method to manage limited bandwidth b. A method of connecting two hosts synchronously c. A method to ensure data integrity d. A method to check data for viruses prior to transmission

4. Which function best describes flow control?

a. Checks data packets for integrity and legitimacy prior to transmission b. Avoids traffic backup by cycling host quickly through alternate send and

receive modes during peak traffic periods c. Connects two hosts over an exclusive high-speed link for critical data

transfer d. Avoids the problem of a host at one side of the connection, overflowing

the buffers in the host at the other side


5. Which of the following occurs in the transport layer when a connection is first established between computers in network?

a. Acknowledgment and retransmission b. Encapsulation and broadcasting c. Synchronization and acknowledgment. d. Recovery and flow control

6. Which of the following occurs in the transport layer when data congestion occurs?

a. Broadcasting b. Windowing c. Error recovery d. Flow control

7. Which layer of the OSI model handles flow control and error recovery?

a. Application b. Presentation c. Transport d. Network

8. What technique allows multiple applications to share a transport connection?

a. Broadcasting b. Synchronicity c. Encapsulation d. Segmentation

9. Which best describes segmentation?

a. Breaks data into smaller packets for faster transmission b. Switches hosts from send to receive mode continuously during peak

traffic periods c. Allows multiple applications to share a transport connection d. Transfers data from the presentation layer to the network layer for

encoding and encapsulation


10. What method controls the amount of information transferred end-to-end and helps enable TCP reliability?

a. Broadcasting b. Windowing c. Error recovery d. Flow control

11. If the window size is set to 1, when would an acknowledgment of data packet receipt be sent back to the source?

a. After one packet b. After two packets c. After three packets d. After four packets

12. If the window size is set to 3, when would an acknowledgment of data packet receipt be sent back to the source?

a. After one packet b. After three packets c. After six packets d. After nine packets


Chapter 13

Layer 5: The Session Layer

Introduction

The session layer, which is Layer 5 of the OSI reference model, establishes, manages, and terminates sessions between applications. Essentially, the session layer coordinates service requests and responses that occur when applications communicate between different hosts.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following question in the space provided.

• Session layer functions coordinate communication interactions between applications. Give an example of how these communication interactions are coordinated.

Communication sessions consist of service requests and service responses that occur between applications located in different network devices. These requests and responses are coordinated by protocols implemented at the session layer. Some examples of session layer implementations include Zone Information Protocol (ZIP); the AppleTalk protocol, which coordinates the name-binding process; and Session Control Protocol (SCP), the DECnet Phase IV session layer protocol.



Collision In Ethernet, the result of two nodes transmitting simultaneously. The frames from each device impact and are damaged when they meet on the physical media. Protocol 1) Formal description of a set of rules and conventions that govern how devices on a network exchange information. 2) Field within an IP datagram that indicates the upper-layer (Layer 4) protocol sending the datagram.

Session 1) Related set of communications transactions between two or more network devices. 2) In SNA, a logical connection enabling two MAUs to communicate.

Session layer Layer 5 of the OSI reference model. This layer establishes, manages, and terminates sessions between applications and manages data exchange between presentation layer entities. Corresponds to the data flow control layer of the SNA model.


TWS (two-way simultaneous) Mode that allows a router configured as a primary SDLC station to achieve better utilization of a full-duplex serial line. When TWS is enabled in a multidrop environment, the router can poll a secondary station and receive data from that station while it sends data to or receives data from a different secondary station on the same serial line.

Focus Questions

1. Which of the following are Layer 5 protocols?

a. (NFS) Network File System b. (SQL) Structured Query Language c. (RPC) Remote Procedure Call d. X Window System e. (ASP) AppleTalk Session Protocol f. DNA (Digital Network Architecture) g. SCP (Session Control Protocol)

2. In a session, check points used for what?

Check points are used to separate parts of a session, previously referred to as dialogues.

3. What is dialog separation?

Dialog separation is the orderly initiation, termination, and management of communication.

4. When in the session layer, what are the responsibilities of both hosts when sending a message?

Host A session layer sends a synchronization message to host B, at which time both hosts perform the following routine: a. Back up the particular files b. Save the network settings c. Save the clock settings d. Make note of the endpoint in the conversation


5. What type of two-way communication is the session layer most involved in?

If two-way simultaneous communication is allowed, the session layer does little in the way of managing the conversation, and allows the other layers of the communicating computers to manage the conversation. Two way-alternate communication involves the use of a session layer data token, which allows each host to take turns. This is similar to the way a Layer 2 Token Ring handles Layer 1 collisions.

6. What is the responsibility of the session layer?

The session layer establishes, manages, and terminates sessions between applications.

7. When computers communicate with each other, what is the dialog process called that determines which computer takes on the role of the client and which takes on the role of the server?

Communication between two computers involves many mini-conversations, thus ensuring that the two computers can communicate effectively. One requirement of these mini-conversations is that each host plays dual roles: requesting service, like a client; and, replying with service, like a server. Determining which role they are playing at any given moment is called dialog control.




1. Which layer of the OSI model establishes, manages, and terminates communication between applications?


2. Which best describes the function of session layer?

a. Establishes, manages, and terminates communications between applications.

b. Supports communication between programs like electronic mail, file transfer, and Web browsers

c. Provides transport services from the host to the destination d. Translates between different data formats such as ASCII and EBCDIC


Chapter 14

Layer 6: The Presentation Layer

Introduction

Layer 6 of the OSI reference model, the presentation layer, provides code formatting and conversion. Code formatting is used to make sure that applications have meaningful information to process. If necessary, this layer can translate between different data formats. The presentation layer is not only concerned with the format and representation of data. It also is concerned with the data structure that the programs used. Thus, Layer 6 arranges for Layer 7 how data will be organized when it is transferred.

Concept Questions


• Layer 6 standards also guide how graphic images are presented. What standards for graphic images do Layer 6 employ?

PICTA picture format used to transfer QuickDraw graphics between programs on the MAC operating system

Tagged Image File Format (TIFF)A format for high-resolution, bitmapped images

Joint Photographic Experts Group (JPEG)A graphics format used most often to compress still images of complex pictures and photographs

Musical Instrument Digital Interface (MIDI)Standard for digitized music

Motion Picture Experts Group (MPEG)Standard for the compression and coding of motion video for CDs and digital storage

QuickTimeStandard that handles audio and video for programs on both MAC and PC operating systems

• Explain how Layer 6 structures the data for Layer 7 to transfer. After receiving data from the application layer, the presentation layer performs one or all of its functions on the data before it sends it to the session layer. At the receiving station, the presentation layer takes the data from the session layer and performs the required functions before passing it to the application layer.

⇒ Data formatting (presentation)

⇒ Data encryption

⇒ Data compression




ASCII (American Standard Code for Information Interchange) American Standard Code for Information Interchange. An 8-bit code for character representation (7 bits plus parity).

Compression The running of a data set through an algorithm that reduces the space required to store or the bandwidth required to transmit the data set.

EBCDIC (Extended Binary Coded Decimal Interchange Code) Extended binary coded decimal interchange code. Any of a number of coded character sets developed by IBM consisting of 8-bit coded characters. This character code is used by older IBM systems and telex machines.

Encryption The application of a specific algorithm to data so as to alter the appearance of the data making it incomprehensible to those who are not authorized to see the information.

Presentation layer This layer ensures that information sent by the application layer of one system will be readable by the application layer of another. The presentation layer also is concerned with the data structures used by programs and therefore negotiates data transfer syntax for the application layer.

Focus Questions

1. What are the three functions of the presentation layer?

Data formatting (presentation) Data encryption Data compression

2. At the receiving station, from which layer does the presentation layer get the data?

The presentation layer takes the data from the session layer and performs the required functions before passing it to the application layer.

3. What types of computers most often use EBCDIC?

EBCDIC is used by older IBM systems and telex machines.

4. What is a JPEG?

JPEG (Joint Photographic Experts Group) is a graphics format used most often to compress still images of complex pictures and photographs


5. In the presentation layer, what does the algorithm search for to help shrink the size of a file?

The algorithm searches each file for repeating bit patterns and then replaces them with a token. A token is a much shorter bit pattern that represents the long pattern.

6. What type of program uses binary files?

Programs such as FTP use the binary file type to transfer files. Networks use many different types of files.

7. What are the two file formats used by the Internet to display images?

The Internet uses two binary file formats to display images: GIF and JPEG. Any computer with a reader for the GIF and JPEG file formats can read these file types, regardless of the type of computer.

8. What type of file format is used as a set of directions for displaying a page on a web browser?

Hypertext Markup Language (HTML), the language of the Internet, tells a browser whether to display text or to provide a hyperlink to another URL. HTML is not a programming language, but it is a set of directions for displaying a page.




1. Which layer of the OSI model layer can translate between different data formats, such as ASCII and EBCDIC?


2. Which layer of the OSI model layer guides how graphic images, sound, and video are presented?


3. Which best describes the function of the presentation layer?

a. Establishes, manages, and terminates applications b. Supports communication between programs like electronic mail, file

transfer, and web browsers c. Guides how graphic images, sound, and video are handled d. Provides transport services from the host to the destination

4. Which best describes the function of the presentation layer?

a. Establishes, manages, and terminates applications b. Supports communication between programs like electronic mail, file

transfer, and web browsers c. Provides transport services from the host to the destination d. Translates between different data formats such as ASCII and EBCDIC


5. Which layer of the OSI model layer handles data encryption?


6. ASCII, encryption, QuickTime, JPEG are all typical of which layer?

a. Presentation b. Transport c. Application d. Session


Chapter 15

Layer 7: The Application Layer

Introduction

In the context of the OSI reference model, the application layer, Layer 7 of the OSI reference model, supports the communicating component of an application. A computer application can require only information that resides on its computer. However, a network application might have a communicating component from one or more network applications. A word processor might incorporate a file-transfer component that allows a document to be transferred electronically over a network. This file-transfer component qualifies the word processor as an application in the OSI context and belongs in Layer 7 of the OSI reference model. Web browsers, such as Netscape Navigator and Internet Explorer, also have data-transfer components. An example of this is when you go to a web sitethe web pages are transferred to your computer.

Concept Questions


• The application layer (Layer 7) provides services to application processes that are outside of the OSI model. What services are provided?

⇒ Provides services to application processes that are outside of the OSI model

⇒ Identifies and establishes the availability of intended communication partners

⇒ Synchronizes cooperating applications ⇒ Establishes agreement on procedures for error recovery and control of

data integrity. • The application layer identifies and establishes the availability of intended

communication partners and the resources required to connect with them. What are these resources? The application layer is the OSI layer closest to the end user. This determines whether sufficient resources exist for communication between systems (such as electronic mail, file transfer, and terminal emulation). The application layer provides a direct interface to the rest of the OSI model for network applications (such as browser, e-mail, FTP, and Telnet) or an indirect interface for standalone applications (such as word processors, spreadsheets, and presentation managers) with a network redirector.



Define the following terms as completely as you can. Use the online Chapter 15 of the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition, material for help.

Application layer Layer 7 of the OSI reference model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside of the OSI model. The application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications, and establishes agreement on procedures for error recovery and control of data integrity. Corresponds roughly with the transaction services layer in the SNA model.

Client Node or software program (front-end device) that requests services from a server. Client/server computing Term used to describe distributed computing (processing) network systems in which transaction responsibilities are divided into two parts: client (front end) and server (back end). Both terms (client and server) can be applied to software programs or actual computing devices. Also called distributed computing (processing).

DNS (Domain Name System) System used in the Internet for translating names of network nodes into addresses.

Domain server Server that exists on a local-area network responsible for sharing services and authenticating network access.

FTP (File Transfer Protocol) Application protocol, part of the TCP/IP protocol stack, used for transferring files between network nodes.

HTML (Hypertext Markup Language) Simple hypertext document formatting language that uses tags to indicate how a given part of a document should be interpreted by a viewing application, such as a WWW browser.

Hypertext Electronically stored text that allows direct access to other texts by way of encoded links. Hypertext documents can be created using HTML and often integrate images, sound, and other media that are commonly viewed using a WWW browser.

IP address 1) A 32-bit address assigned to hosts using TCP/IP. An IP address belongs to one of five classes (A, B, C, D, or E) and is written as 4 octets separated with periods (dotted-decimal format). Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing; whereas, the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. Also called an Internet address. 2) Command used to establish the logical network address of this interface.

Redirector Software that intercepts requests for resources within a computer and analyzes them for remote access requirements. If remote access is required to satisfy the request, the redirector forms an RPC and sends the RPC to lower-layer protocol software for transmission through the network to the node that can satisfy the request.


Server Node or software program that provides services to clients. Telnet Command used to verify the application layer software between source and destination stations. This is the most complete test mechanism available.

URL (Universal Resource Locator) Standardized addressing scheme for accessing hypertext documents and other services using a WWW browser.

Focus Questions

1. To which other OSI layers does the application layer provide service?

The application layer does not provide services to any other OSI layer.

2. What is a network application that uses the direct interface provided by the application layer?

A word processor might incorporate a file-transfer component that allows a document to be transferred electronically over the network.

3. What is a network application that uses the indirect interface provided by the application layer?

The application layer provides a direct interface for the rest of the OSI model, by using network applications (for instance, WWW, e-mail, FTP, Telnet), or an indirect interface, by using standalone applications (for instance, word processors, spreadsheets, presentation managers, network redirector).

4. Where is the server side of a client/server application located?

These applications (such as FTP, web browsers, and e-mail) all have two components that allow them to function: the client side and the server side. The client side is located on the local computer and is the requestor of the services. The server side is located on a remote computer and provides services in response to the clients requests.

5. What is the looped routine constantly repeated by a client/server application?

A client/server application works by constantly repeating the following looped routine: client-request, server-response; client-request, server-response; and so on.

6. What does DNS do?

Domain name system (DNS) is a device on a network that manages domain names and responds to requests from clients to translate a domain name into the associated IP address.

7. Which protocol do file utility programs use to copy and move files between remote sites?

File utility programs use the FTP protocol for copying and moving files between remote sites.


8. Which protocol do remote-access programs use to directly connect to remote resources?

Remote-access programs use the Telnet protocol for directly connecting to remote resources.




1. Which layer of the OSI model supports communication between programs, such as e-mail, file transfer, and web browsers?


2. Which best describes the function of the application layer?

a. Establishes, manages, and terminates applications b. Supports communication between programs like e- mail, file transfer, and

web browsers c. Provides transport services from the host to the destination d. Translates between different data formats such as ASCII and EBCDIC

3. Which is a network application?

a. E-mail b. Word processor c. Web browser d. Spreadsheet

4. Which is a computer application?

a. Remote access b. File transfer c. Web browser d. E-mail

5. E-mail and file transfer are typical functions of which layer in the OSI model?

a. Transport b. Network c. Application d. Presentation

128 - 239 Engineering Journal and Workbook, Vol. I, 2nd Ed. – Chapter 16 Copyright © 2002 Cisco Systems, Inc.

Chapter 16

WANs and Routers Introduction

One major characteristic of a wide-area network (WAN) is that the network operates beyond the local LAN’s geographic scope. It uses the services of carriers, such as Regional Bell Operating Companies (RBOCs), Sprint, and MCI. WANs use serial connections of various types to access bandwidth over wide-area geographies. By definition, the WAN connects devices separated by wide areas. WAN devices include the following:

• Routers, which offer many services, including internetworking and WAN interface ports

• Switches, which connect to WAN bandwidth for voice, data, and video communication

• Modems, which interface voice-grade services and channel service units/digital service units

• CSU/DSUs that interface T1/E1 services and Terminal Adapters/Network Termination 1

• TA/NT1s that interface Integrated Services Digital Network (ISDN) services

• Communication servers, which concentrate on dial-in and dial-out user communication

Concept Questions


• A WAN is used to interconnect local-area networks (LANs) that are typically separated by a large geographic area. A WAN operates at the OSI reference model physical and data link layers. The WAN provides for the exchange of data packets/frames between routers/bridges and the LANs that they support. Draw a WAN that includes three LANs. Student should sketch a WAN with three connected LAN segments. Students should use the appropriate symbols to represent all network devices.


• Compare and contrast WANs and LANs layer by layer. LANs use deterministic and nondeterministic communication to allow access to the media. The transport of data typically is seen by numerous nodes on a segment. Layer 1 communication runs across UTP, STP, fiber, and coax lines. Connectors used include, but are not limited to, RJ-45, ST, SC, FC, AUI, and BNC connectors. Communication is typically much faster than that of wide-area links. LANs use 802.2, 802.3, 802.4, or 802.5 Layer 2 frame encapsulation. WANs operate beyond the local LAN’s geographic scope. They use the services of carriers such as Regional Bell Operating Companies (RBOCs) and Sprint and MCI. They use serial connections of various types to access network bandwidth. Layer 1 connections are generally V.35, RS232, RS449, and RJ-48 connectors. Communication is generally across a point-to-point, circuit, or packet-switched environment. WANs use layer 2 encapsulations such as Frame Relay, HDLC, SDLC, PPP, and X.25.



CSU (channel service unit) Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to together with DSU, as CSU/DSU. See also DSU.

DCE (Data Communications Equipment (EIA expansion) or data circuit-terminating equipment (ITU-T expansion)) The devices and connections of a communications network that comprise the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE. Compare with DTE.

DSU (data service unit) Device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU also is responsible for such functions as signal timing. Often referred to together with CSU, as CSU/DSU. See also CSU.

DTE (data terminal equipment) Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocol translators, and multiplexers. Compare with DCE.

E1 Wide-area digital transmission scheme used predominantly in Europe that carries data at a rate of 2.048 Mbps. E1 lines can be leased for private use from common carriers. Compare with T1.

Frame Relay Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it is generally considered a replacement.


HDLC (High-Level Data Link Control) Bit-oriented synchronous data link layer protocol developed by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.

ISDN (Integrated Services Digital Network) Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice, and other source traffic.

PPP (Point-to-Point Protocol) A successor to SLIP, PPP provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.

PTT (Post, Telephone, and Telegraph) Government agency that provides telephone services. PTTs exist in most areas outside North America and provide both local and long-distance telephone services.

RBOC (Regional Bell Operating Company) Local or regional telephone company that owns and operates telephone lines and switches in one of seven U.S. regions. The RBOCs were created by the divestiture of AT&T. Also called Bell Operating Company (BOC).

T1 Digital WAN carrier facility. T1 transmits DS-1-formatted data at 1.544 Mbps through the telephone-switching network, using AMI or B8ZS coding. Compare with E1.

Focus Questions

1. Name and briefly describe four WAN devices.

WAN devices include routers (which offer internetworking and WAN interface ports); switches (for sharing bandwidth); modems, CSU/DSUs, and terminal adapters (which allow a variety of data connection services); and communication servers (which concentrate dial-in and dial-out user communications).

2. Name two ways in which WANs differ from LANs.

WANs operate over a large geographical area (LANs do not); WANs emphasize access over serial interfaces operating at lower speeds to ensure reliability. (LANs can operate reliably at very high speeds with multiple access.)

3. What do the acronyms DTE and DCE stand for?

DTE stands for data terminal equipment, which refers to the end of the user’s devices on a WAN link. DCE stands for data circuit-terminating equipment, which refers to the end of the WAN provider’s side of the communication facility.

4. List three WAN physical layer standards.

Three WAN physical layer standards commonly used are EIA/TIA-232, V.35, and X.21.


5. List four WAN data link layer protocols.

Four WAN data link layer protocols are HDLC (High-Level Data Link Control), Frame Relay (a simplified version of HDLC framing), PPP (Point-to-Point protocol), and ISDN (Integrated Services Digital Network).



The following questions help you review for the CCNA exam. Answers also appear in Appendix A, “Answers to the CCNA Exam Review Questions,” from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which of the following best describes a WAN?

a. Connects LANs that are separated by a large geographic area b. Connects workstations, terminals, and other devices in a metropolitan

area c. Connects LANs within a large building d. Connects workstations, terminals, and other devices within a building

2. Which of the following are examples of WANs?

a. Token Ring and ARCnet b. Frame Relay and SMDS c. Star and Banyan VINES d. CSU/DSU and ARCview

3. What service does a WAN provide to LANs?

a. High-speed multiple access to data networks b. IP addressing and secure data transfer c. Exchanging data packets between routers and the LANs those routers

support d. Direct routing with error checking

4. What type of connections do WANs use that LANs typically do not use?

a. Parallel, lower speed b. Multiple, higher speed c. Multiple, lower speed d. Serial, lower speed.

5. At which layers of the OSI model does a WAN operate?

a. Physical and application b. Physical and data link c. Data link and network d. Data link and presentation


6. Which layers of the OSI models do WAN standards describe?

a. Data link and network b. Data link and presentation c. Physical and application d. Physical and data link

7. How do WANs differ from LANs?

a. Typically exist in defined geographic areas b. Provide high-speed multiple access services c. Use tokens to regulate network traffic d. Use services of common carriers

8. How do WANs differ from LANs?

a. Emphasize access over serial interfaces operating at lower speeds b. Provide high-speed multiple access services c. Typically exist in defined geographic areas d. Use tokens to regulate network traffic

9. How are operational and functional connections for WANs obtained?

a. From your local telephone company b. From InterNIC c. From Regional Bell Operating Companies (RBOCs) d. From the WWW Consortium

10. What do the WAN physical layer standards describe?

a. Interface between SDLC and HDLC b. How frames are sent and verified c. How voice and data traffic are routed d. Interface between DTE and DCE

11. Which best describes what WAN data link protocols define?

a. How frames are carried between systems on a single data link b. Methods for determining optimum path to a destination c. How data packets are transmitted between systems on multiple data links d. Methods for mapping IP addresses to MAC addresses


12. Which is a WAN data link protocol?

a. TCP/IP b. Point-to-Point Protocol c. EIGRP d. OSPF

13. Which is a WAN data link protocol?

a. TCP/IP b. OSPF c. EIGRP d. Frame Relay

14. Which best describes data terminal equipment (DTE)?

a. Physical connection between networks and users b. Generates clocking signals to control network traffic c. Device at the user end of a network d. Physical devices such as modems and interface cards

15. Which is an example of data terminal equipment (DTE)?

a. Interface card b. Modem c. Computer d. CSU/DSU

16. Which best describes data circuit-terminating equipment (DCE)?

a. Device at the user end of a network b. Serves as data source and/or destination c. Physical devices such as protocol translators and multiplexers d. End of the WAN provider’s side of the communication facility

17. Which is an example of data circuit-terminating equipment (DCE)?

a. Multiplexer b. Modem c. Translator d. Computer


18. Which best describes High-Level Data Link Control (HDLC)?

a. Digital service that transmits voice and data over existing phone lines b. Uses high-quality digital facilities—fastest WAN protocol c. Provides router-to-router and host-to-network connections over

synchronous and asynchronous circuits d. Supports point-to-point and multipoint configurations, and uses frame

characters and checksums

19. Which WAN protocol can be described as supporting point-to-point and multipoint configurations?

a. HDLC b. Frame Relay c. PPP d. ISDN

20. Which WAN protocol can be described as using frame characters and checksums?

a. ISDN b. Frame Relay c. PPP d. HDLC

21. Which best describes Frame Relay?

a. Uses high-quality digital facilities—fastest WAN protocol b. Supports point-to-point and multipoint configurations, and uses frame

characters and checksums c. Digital service that transmits voice and data over existing telephone lines d. Provides router-to-router and host-to-network connections over

synchronous and asynchronous circuits

22. Which WAN protocol can be described as using high-quality digital facilities?



23. Given the following WAN protocols, which can be described as the fastest?

a. HDLC b. PPP c. Frame Relay d. ISDN

24. Which best describes PPP?

a. Uses high-quality digital facilities—fastest WAN protocol b. Supports point-to-point and multipoint configurations, and uses frame

characters and checksums c. Provides router-to-router and host-to-network connections over

synchronous and asynchronous circuits d. Digital service that transmits voice and data over existing telephone lines

25. Given the following WAN protocols, which can be described as the fastest?


26. Which best describes ISDN?

a. Digital service that transmits voice and data over existing phone lines. b. Provides router-to-router and host-to-network connections over

synchronous and asynchronous circuits c. Uses high quality digital facilities—fastest WAN protocol d. Supports point-to-point and multipoint configurations, and uses frame

characters and checksums

27. Which WAN protocol can be described as a digital service that transmits voice and data over existing telephone lines?



Chapter 17

Router CLI Introduction

You configure Cisco routers from the user interface that runs on the router console or terminal. You also can configure Cisco routers by using remote access. You must log in to the router before you can enter an EXEC command. For security purposes, the router has two levels of access to commands:

• User mode—Typical tasks include those that check the router status. In this mode, router configuration changes are not allowed.

• Privileged mode—Typical tasks include those that change the router configuration.

Concept Questions


• You can use the router to do the following:

⇒ Log in with the user password.

⇒ Enter privileged mode with the enable password.

⇒ Disable or quit.

What procedures would you follow to log in to the router? When you first log in to a router, you see a user-mode prompt: Router>

At the > prompt, type enable

At the password prompt, enter the password that has been set with the enable secret command. When you have completed the login steps, the prompt changes to a pound sign (#) because you are now in privileged mode. From privileged mode, you can access modes such as global configuration mode and other specific configuration modes.


Logging in to and out of the Router Router con0 is now available.

Press RETURN to get started.

User Access Verification

Password:

Router>

Router> enable

Password:

Router#

Router# disable

• You can use the following advanced help features: Command completion and prompting Syntax checking

Why would you need to use syntax checking? You can use the following advanced editing features:

⇒ Automatic line scrolling

⇒ Cursor controls

⇒ History buffer with command recall

⇒ Copy and paste, which are available on most laptop computers

• Why is it important to have two different levels of access of commands? Commands available at user level are a subset of the commands available at the privileged level. For the most part, these commands enable you to display information without changing router configuration settings. You may want to have multiple administrators with varied levels of access. To access the full set of commands, you must first enable privileged mode.



Privileged mode Typical tasks include those that change the router configuration.

User mode Typical tasks include those that check the router status. In this mode, router configuration changes are not allowed.


Focus Questions

1. How do you use a router?

To configure Cisco routers, you must either access the user interface on the router with a terminal or access the router remotely. When accessing a router, you must log in to the router before you enter any other commands.

2. Distinguish between user mode and privileged mode.

User mode enables you to check router status; privileged mode enables you to actually change the router’s configuration.

3. In Cisco IOS, what is the user mode prompt and what is the privileged mode prompt?

The > is the user-mode prompt; the # is the privileged-mode prompt.

4. What must you type at the user or privileged mode prompts to display a list of commonly used commands?

You must type a ? to display the list of commonly used commands.

5. When in user mode, what must you do to enter privileged mode?

You must type ena (short for enable) and then a password.

6. If you are unsure of the syntax or arguments for a command, what feature can be of great help to you?

If you guess at the command syntax and arguments, the Cisco IOS context-sensitive help will highlight your errors and suggest corrections. Additionally, by adding a space and then the question mark after a partial command, you will get hints about how to proceed.




1. What are the two modes of access to router commands for Cisco routers?

a. User and privileged b. User and guest c. Privileged and guest d. Guest and anonymous

2. Why are there two modes of access to router commands on Cisco routers?

a. One mode is for remotely working on the router; whereas, the other mode is for directly working on the router via a console.

b. One mode, which has many automatic sequences, is for new users; whereas, the other mode is for experienced users who can issue direct commands.

c. One mode lets a number of users see what’s happening on the router; whereas, the other mode lets a few users change how the router operates.

d. One mode is for the initial router configuration and startup; whereas, the other mode is for maintaining, updating, and changing the router after initial startup.

3. What can be done only in privileged mode on Cisco routers?

a. Change the configuration b. Enter commands c. Check routing tables d. All of the above

4. How do you switch from user to privileged mode on Cisco routers?

a. Type admin and enter a password.

b. Type root and enter a password.

c. Type enable and enter a password.

d. Type privileged and enter a password.


5. What happens if you type enable on a Cisco router user interface?

a. You switch to user mode. b. The last command entered is activated. c. A new LAN is added to the router table. d. You switch to privileged mode.

6. Which IOS command is not available in the user-mode?

a. show

b. ppp

c. trace

d. ping 7. On a Cisco router which of the following is the user-mode prompt?

a. # b. > c. < d. |#

8. On a Cisco router which if the following is the privileged-mode prompt?

a. # b. > c. < d. |#

9. How do you log out of a Cisco router?

a. Type Control-Q b. Type quit c. Type exit d. Type Control-X

10. How can you get a list of commonly used commands from a Cisco router user interface?

a. Type list

b. Type Control-C

c. Type Control-?

d. Type ?


11. What does the “More” prompt at the bottom of a screen on a Cisco router user interface mean?

a. Multiple screens are available as output. b. Additional detail is available in the manual pages. c. Multiple entries are required in the command. d. Additional conditions must be stated.

12. How do you get to the next screen if “More” is indicated at the bottom of the current screen on a Cisco router user interface?

a. Press the Page Down key. b. Press the spacebar. c. Press the End key. d. Press the Tab key.

13. Which keystroke(s) automatically repeat(s) the previous command entry on a Cisco router user interface?

a. Left arrow b. Right arrow c. Control+R d. Control+P

14. What happens if you type ? in user-mode or privileged-mode?

a. You see all users logged in to the router. b. You list the last command you typed. c. You are presented with a list of commands. d. You find out which mode you are currently in.

15. What does it mean if you see the symbol ^ on a Cisco router user interface?

a. Indicates location of an error in a command string b. Indicates that you are in Help mode c. Indicates that more information must be entered to complete the

command d. Indicates that you are in privileged mode


16. What would you type at the router user prompt if you want to see what show subcommands are available?

a. ?

b. Command ?

c. Show ?

d. List ?

17. What would you type at the router user prompt if you want to see what configuration subcommands are available?

a. ?

b. Command ?

c. List ?

d. Config ?

18. What command is only available at the privileged access mode?

a. ping

b. show

c. trace

d. All of the above


Chapter 18

Router Components

Introduction

Whether accessed from the console or by a Telnet session through an auxiliary port, the router can be placed in several modes. Each mode provides different functions:

• User EXEC mode—A “look-only” mode in which the user can view some information about the router, but cannot change anything.

• Privileged EXEC mode—Supports the debugging and testing commands, detailed examination of the router, manipulation of configuration files, and access to configuration modes.

• Setup mode—Presents an interactive prompted dialog box at the console that helps the new user create a first-time, basic configuration.

• Global configuration mode—Implements powerful one-line commands that perform simple configuration tasks.

• Other configuration modes—Provide more complicated multiple-line configurations.

• RXBOOT mode—A maintenance mode that can be used, among other things, to recover lost passwords.

Concept Questions


• The router is made up of configurable components. How are these components configured? You can configure a router from many external locations, including the following:

⇒ From the console terminal (a computer connected to the router through a console port) during its installation

⇒ Via modem by using the auxiliary port

⇒ From virtual terminals, after the router has been installed on the network

⇒ From a TFTP server on the network


• The router has modes for examining, maintaining, and changing the components. In the examining mode, what does the router do? User EXEC allows for the execution of basic commands that you can issue to determine the current status of a router. These commands help you obtain vital information that you need when monitoring and troubleshooting router operations.

• The show commands are used for examination. What does the show command examine? It is important to be able to monitor the health and state of your router at any given time. These commands are as follows:

• show version

• show processes

• show protocols

• show memory

• show stacks

• show buffers

• show flash

• show running-config

• show startup-config

• show interface

Among the most used Cisco IOS software EXEC commands are show running-config and show startup-config. These commands enable an administrator to see the current running configuration on the router or the startup configuration commands that the router will use on the next restart.

• Use CDP to show entries about neighbors.

• Access other routers with Telnet.

• Test network connectivity layer by layer. Testing commands include ping, trace, and debug. What is the difference between trace and ping? The ping command sends a packet to the destination host and then waits for a reply packet from that host. You can use the ping user EXEC command to diagnose basic network connectivity. The trace command is the ideal tool for finding where data is being sent in your network. The trace command is similar to the ping command, except that, instead of testing end-to-end connectivity, trace tests each step along the way. This operation can be performed at either the user or the privileged EXEC levels.




CDP (Cisco Discovery Protocol) Media- and protocol-independent device-discovery protocol that runs on all Cisco-manufactured equipment including routers, access servers, bridges, and switches. Using CDP, a device can advertise its existence to other devices and receive information about other devices on the same LAN or on the remote side of a WAN. Runs on all media that support SNAP, including LANs, Frame Relay, and ATM media.

CPU (central processing unit) The part of a computer that controls all the other parts. It fetches instructions from memory and decodes them. This may cause it to transfer data to or from memory or to activate peripherals to perform input or output.

DRAM (dynamic random-access memory) RAM that stores information in capacitors that must be periodically refreshed. Delays can occur because DRAMs are inaccessible to the processor when refreshing their contents. However, DRAMs are less complex and have greater capacity than SRAMs.

Interface 1) Connection between two systems or devices. 2) In routing terminology, a network connection. 3) In telephony, a shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals. 4) The boundary between adjacent layers of the OSI model.

NVRAM (nonvolatile RAM) RAM that retains its contents when a unit is powered off. In Cisco products, NVRAM is used to store configuration information. ping Command that uses the ICMP protocol to verify the hardware connection and the logical address of the network layer. This is a very basic testing mechanism.

RAM (random-access memory) Volatile memory that can be read and written by a microprocessor. Telnet Command used to verify the application layer software between source and destination stations. This is the most complete test mechanism available.

TFTP (Trivial File Transfer Protocol) Simplified version of FTP that allows files to be transferred from one computer to another over a network. trace Command that uses Time-To-Live (TTL) values to generate messages from each router used along the path. This is very powerful in its capability to locate failures in the path from the source to the destination.


Focus Questions

1. Diagram the internal components (subsystems) of a modern multimedia PC. Diagram the external features of a modern multimedia PC.

Refer to diagrams in the Companion Guide.

2. List three external configuration sources for Cisco routers.

Routers may be configured from the console terminal through the console port, via a modem using the auxiliary port, and from virtual terminals or a TFTP server once it is on a network.

3. List and describe the internally configurable components of a router.

Internal configuration components include RAM (stores routing tables, ARP cache, and running configuration file), NVRAM (stores the router’s backup configuration file; retains content even when powered down), Flash (erasable, reprogrammable ROM, holds the operating system image), ROM(contains power-on diagnostics, a bootstrap program, and operating system software) and interfaces (network connections through which packets enter and exit the router).

4. List at least seven commands that can show router status and the configurable components about which they display information.

Commands for examining a router’s status include the following: show version (RAM IOS) show processes cpu and show processes (RAM programs) show running-config (RAM active configuration file) show mem, show stacks, show buffers (RAM tables and buffers) show startup-config

show config (NVRAM), show flash (Flash) show interfaces (Interfaces)

5. Briefly describe what Cisco Discovery Protocol (CDP) show cdp neighbors can tell you about a network.

The command show cdp neighbors works at the data link layer to display the following information: neighbor device ID, local port type and number, decremental holdtime value in seconds, the neighbor’s device capability code, the hardware platform of the neighbor, and the neighbor’s remote port type and number.


6. Using the OSI model and the commands telnet, ping, trace, show ip route, and show interface, describe the basic testing of a network.

The basic testing of a network should proceed from Layer 7 (using telnet to access various routers), to Layer 3 (using ping, trace, and show ip route to learn logical address information about the network), and then to Layers 3, 2, and 1 (using show interface to learn about specific port configurations and whether specific links are alive), and then on to Layer 1 (specific medium tests).




1. Which of the following describes a location from which a router is configured?

a. After it is installed on the network, a router can be configured from virtual terminals.

b. Upon initial configuration, a router is configured from the virtual terminals. c. After it is installed on the network, a router can be configured via modem

from the console terminal. d. Upon initial configuration, a router is configured via modem using the

auxiliary port.

2. Which of the following does not describe external configuration of routers?

a. Upon initial configuration, a router is configured from the console terminal.

b. The router can be connected via modem using the console port. c. After it is installed, a router is configured from the console terminal. d. Configuration files can be downloaded from a TFTP server on the

network.

3. Which of the following router components has these characteristics: stores routing tables, fast-switching cache, and packet hold queues?

a. NVRAM b. RAM/DRAM c. Flash d. ROM

4. Which of the following router components has these characteristics: holds the operating system and microcode; retains its contents when you power down or restart; and allows software updates without replacing chips?

a. NVRAM b. RAM/DRAM c. Flash d. ROM


5. Which of the following best describes the function of NVRAM?

a. Provides temporary and/or running memory for the router’s configuration file while the router is powered on.

b. Stores the router’s backup configuration file. The content is retained when you power down or restart.

c. Holds the operating system image and microcode and enables you to update software without removing and replacing chips on the processor.

d. Contains power-on diagnostics, a bootstrap program, and operating system software.

6. Which of the following does not describe a function of working storage RAM in a router?

a. A bootstrap program performs tests and then loads the Cisco IOS software into memory.

b. A saved version of the configuration file is accessed from NVRAM and loaded into main memory when the router initializes.

c. The EXEC part of the IOS software handles packet buffering and the queuing of packets.

d. The operating system image is usually executed from the main RAM and loaded from an input source.

7. Which of the following is the router mode that supports debugging and testing commands, manipulation of configuration files, and detailed examination of the router?

a. Global configuration mode b. RXBOOT mode c. Privileged EXEC mode d. Setup mode

8. Which of the following describes functions of the user EXEC mode of a router?

a. Presents an interactive prompted dialog that helps the new user create a first-time basic configuration

b. Implements powerful one-line commands that perform simple configuration tasks

c. Used for recovery from catastrophe, such as to recover lost passwords d. Allows the user to view some information about the router but not change

anything


9. If you are in global configuration mode, what does the router prompt look like?

a. router #

b. router (config) #

c. router-config #

d. r-config #

10. When you are in user mode, what does the router prompt look like?

a. router -

b. router >

c. router #

d. router

11. What is the command you enter to gain access to privileged EXEC mode?

a. ena

b. p exec

c. exec

d. enable p-exec

12. Which of the following correctly describe the function of a router status command?

a. show version—Displays configuration of the system hardware, the names and sources of configuration files, and the boot images.

b. show mem—Displays statistics about the router’s memory, including memory free pool statistics.

c. show buffers—Displays statistics for the buffer pools on the router. d. All of the above.

13. If you type ? show at the router > prompt, what appears on the screen?

a. Nothing, this is not a valid command. b. All the items that can be shown in user mode. c. The status of the router. d. Information about the version of the IOS that is currently running.


14. Which of the following describes a function of the show running-config Cisco IOS command?

a. It enables an administrator to see the image size and startup configuration commands the router will use on the next restart.

b. It displays a message at the top showing how much nonvolatile memory has been used.

c. It enables an administrator to see the configuration of the processes and interrupt routines.

d. It enables an administrator to see the current running configuration on the router.

15. Which of the following describes a function of the show startup-config Cisco IOS command?

a. It enables an administrator to see the current running configuration on the router.

b. Display the backup configuration file. c. It enables an administrator to see the reason for the last system reboot. d. It displays this message at the top: Current Configuration.

16. The show interface serial Cisco IOS router command can display which one of the following lines of information?

a. IOS 4500 Software (C4500-J-M), Experimental Version 11.2. b. DECNET routing is enabled. c. Serial1 is up, line protocol is up. d. System image file is c4500-j-mz.

17. The show version Cisco IOS router command can display which one of the following lines of information?

a. IOS 4500 Software (C4500-J-M), Experimental Version 11.2. b. Hardware is MK5025. c. Internet Protocol routing is enabled. d. Internet address is 183.8.64.129.

18. The show protocols Cisco IOS router command can display which one of the following lines of information?

a. Serial1 is up, line protocol is up. b. Compiled Fri 28-Jun-96. c. AppleTalk routing is enabled. d. ROM; System Bootstrap, Version 5.1(1).


19. What kind of information cannot be obtained when you enter show interface in the user mode?

a. The MAC address for all interfaces b. The IP address for all interfaces c. How many users are logged in to each interface d. The encapsulation protocol for each interface

20. If you type show interface E0 at the prompt router#, which of the following best shows what the first five lines of the response would look like if the interface was up?

a. Ethernet0 is up, line protocol is up Address is 0000.0f92.c54b (bia 0000.0f92.c54b) Internet address is 223.8.151.1/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10sec)

b. Ethernet0 is up, line protocol is up Hardware is Lance, address is 0000.0f92.c54b (bia 0000.0f92.c54b) Internet address is 223.8.151.1/24 ARP type: ARPA, ARP Timeout 05:00:00 Encapsulation ARPA, loopback not set, keepalive set (10sec)

c. Ethernet0 is up, line protocol is up Hardware is Lance, address is 0000.0f92.c54b (bia 0000.0f92.c54b) Internet address is 223.8.151.1/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10sec)

d. Ethernet0 is up, line protocol is up Address is 0000.0f92.c54b (bia 0000.0f92.c54b) Internet address is 223.8.151.1/24 Subnet Mask is 255.255.255.255/24 Encapsulation ARPA, loopback not set, keepalive set (10sec)

21. Which one of the following is a function of Cisco Discovery Protocol (CDP)?

a. Provides a way to use an echo to evaluate the path-to-host reliability b. Provides a way to determine whether a routing table entry exists c. Provides a way to see the current running configuration on the local

router d. Provides a way to access summaries of configurations on directly

connected devices


22. Which of the following is a characteristic of CDP?

a. It runs over OSI Layer 3. b. It allows CDP devices that support different network layer protocols to

learn about each other. c. It obtains information about neighboring devices only if the administrator

enters commands. d. It obtains information only about devices running TCP/IP.

23. What steps does the network administrator have to take to make CDP run at system startup?

a. Type cdp enable at the first router prompt. b. Type cdp enable at the first privilege EXEC router prompt. c. CDP runs automatically at start up. d. Type cdp enable at any prompt at then save the config file.

24. Which of the following is a function of the CDP show command?

a. It displays information about any CDP-enabled router on the network. b. It displays information on a console connected to any node in the

network. c. It helps evaluate delays over network paths and path-to-host reliability. d. It identifies neighboring routers’ host names and IP addresses.

25. Which of the following is not provided by the CDP show command to tell about neighbor routers?

a. Processes list, with information about the active processes b. Port identifier, such as Ethernet0, Serial1, and so forth c. The device’s hardware platform d. Address list, with addresses for supported protocols

26. Which of the following is a function of the cdp enable command?

a. Boots up the Cisco IOS software and implements diagnostic testing b. Displays values of the CDP timers c. Begins CDP’s dynamic discovery function on the router’s interfaces d. Discards expired holdtime values


27. Which of the following is not a function of the show cdp interface command?

a. Displays the values of the CDP timers b. Displays the reasons for system reboot c. Displays the interface status d. Displays the encapsulation used by CDP

28. Which of the following is a function of the show cdp entry [device_name] command?

a. Establishes a connection to a remote router b. Displays the cached CDP entry for every directly connected CDP router c. Enables an administrator to see the IP addresses of the targeted router d. Displays version information about the network protocols running on the

router

29. Which of the following is not a function of the show cdp entry [device_name] command?

a. Displays the cached CDP entry for every directly connected CDP router b. Displays all Layer 3 addresses present on the router c. Displays how long ago the CDP frame arrived from the router d. Displays version information about the router

30. Which of the following is a function of the show cdp neighbors command?

a. Displays the device capability code of remote routers b. Displays the path-to-host reliability of a network connection c. Displays the encapsulation of the protocols used by neighbor routers d. Displays the neighbor’s remote port type and number

31. Which of the following is not a function of the show cdp neighbors command?

a. Displays the cached CDP entry for every directly connected CDP router b. Displays the CDP updates received on any network router c. Displays information like that from show cdp entry when show cdp

neighbors detail is used d. Displays neighbor device IDs


32. Why would you use the show cdp neighbors command?

a. To get a snapshot view of the routers in the network b. To get a overview of the routers that are directly connected to me c. To get the IP addresses for neighboring routers d. To building a routing table for all routers in the network neighborhood

33. Which of the following is a feature of Telnet router operations?

a. Telnet is typically used to connect a router to neighbor routers. b. A router can have only one incoming Telnet session at a time. c. A Telnet session can be suspended and then resumed. d. To initiate a Telnet session, you have to know the name of the host.


Chapter 19

Router Startup and Setup

Introduction

The startup routines for Cisco IOS software have the goal of starting router operations. The router must deliver reliable performance connecting the user networks it was configured to serve. To do this, the startup routines must do the following:

• Make sure that the router comes up with all its hardware tested.

• Find from memory and load the Cisco IOS software that the router uses for its operating system.

• Find from memory and apply the configuration statements about the router, including protocol functions and interface addresses.

The router makes sure that it comes up with tested hardware. When a Cisco router powers up, it performs a power-on self-test (POST). During this self-test, the router executes diagnostics from ROM on all modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After it verifies the hardware functions, the router proceeds with software initialization.

Concept Questions


• The router initializes by loading a bootstrap, the operating system, and a configuration file. What does each of these items do? A bootstrap is a simple, preset operation to load instructions that, in turn, cause other instructions to be loaded into memory or that affect entry into other configuration modes. The operating system (Cisco IOS) can be found in one of several places. The location is disclosed in the boot field of the configuration register. If the boot field indicates a Flash, or network load, boot system commands in the configuration file indicate the exact location of the image. The configuration file saved in NVRAM is loaded into main memory and is executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, set media characteristics, and so on.


• If the router cannot find a configuration file, the router enters setup mode. What does the setup mode do? If no valid configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine referred to as the system configuration dialog, or setup dialog. Setup is not intended as the mode for configuring complex protocol features in the router. You should use setup to bring up a minimal configuration, and then use various configuration-mode commands rather than setup for most router configuration tasks.

• The router stores a backup copy of the new configuration from setup mode. Where does the router store this backup copy? The router stores in NVRAM a backup copy of the current configuration.

• Prepare a flowchart of the startup (boot) sequence of a multimedia PC. Refer to Figure 19-1 in the Companion Guide.



CPU (central processing unit) The part of a computer that controls all the other parts. It fetches instructions from memory and decodes them. This may cause it to transfer data to or from memory or to activate peripherals to perform input or output. erase startup-config Command used to delete the backup configuration file in NVRAM. Reload The event of a Cisco router rebooting, or the command that causes the router to reboot.

Focus Questions

1. What are the three main things the router accomplishes upon startup?

⇒ Makes sure that the router comes up with all its hardware tested.

⇒ Finds and loads the Cisco IOS software that the router uses for its operating system.

⇒ Finds the startup-config file and applies the configuration statements, including protocol functions and interface addresses.


2. Briefly describe the router startup sequence.

Step 1. The generic bootstrap loader executes on the CPU card. Step 2. The location of the IOS image is found by searching the configuration

registers. If the boot field indicates a Flash, or network load, boot system commands in the configuration file indicate the exact location of the image.

Step 3. The operating system image is loaded. Once operational, the OS locates the hardware and software components and lists the results on the console terminal.

Step 4. The configuration file saved in NVRAM is loaded into main memory and is executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, set media characteristics, and so on.

Step 5. If no valid configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine referred to as the system configuration dialog, or setup dialog.

3. What is the main purpose of setup mode?

The main purpose of setup mode is to quickly bring up a minimal configuration for any router that cannot find its configuration from some other source.

4. During the system configuration dialog, you are prompted to set up “global parameters” and to set up “interfaces.” Explain.

Global parameters are used to configure hostnames, enable passwords, enable secret passwords, and global configuration values. When prompted to set up “interfaces,” you need to use the configuration values that you have determined for each interface. These values include IP address, subnet mask, network protocol, and so on.

5. After you have completed the setup command program and your configuration displays, you are asked whether you want to use this configuration. If you answer “yes,” what happens?

If you answer “yes,” the configuration is executed and saved to NVRAM. Your system is now ready to use.




1. Which of the following is the correct order of steps in the Cisco router system startup routine?

a. Locate and load operating system, load bootstrap, test hardware, locate and load configuration file

b. Test hardware, load bootstrap, locate and load operating system, locate and load configuration file

c. Load bootstrap, locate and load configuration file, test hardware, locate and load operating system

d. Test hardware, load bootstrap, locate and load configuration file, locate and load operating system

2. Which of the following is not a step in the Cisco router system startup routine?

a. Load bootstrap b. Power-up hardware self-test c. Enable CDP on each interface d. Locate and load configuration file

3. Which of the following is an important function of the power-on self-test (POST)?

a. To determine the router hardware and software components and list them on the console terminal

b. To cause other instructions to be loaded into memory c. To execute diagnostics that verify the basic operation of router hardware d. To start routing processes, supply addresses for interfaces, and set up

media characteristics

4. Which of the following is an important result of Cisco IOS loading onto a router?

a. Determining the router hardware and software components, and listing them on the console terminal

b. Causing other instructions to be loaded into memory c. Executing diagnostics that verify the basic operation of router hardware d. Starting routing processes, supplying addresses for interfaces, and

setting up media characteristics


5. Which of the following is an important result of the configuration file loading onto a router?

a. Determining the router hardware and software components and listing them on the console terminal

b. Causing other instructions to be loaded into memory c. Executing diagnostics that verify the basic operation of router hardware d. Starting routing processes, supplying addresses for interfaces, and


6. Which of the following is not a function of the router system startup routine?

a. Verifying the routing of protocol packets b. Testing of the basic operations of router hardware c. Causing other instructions to be loaded into memory d. Starting routing processes, supplying addresses for interfaces, and


7. What is the function of the erase startup-config command?

a. It deletes the backup configuration file in NVRAM. b. It deletes the bootstrap image from Flash memory. c. It deletes the current IOS from NVRAM. d. It deletes the current running configuration from Flash memory.

8. What is the function of the reload command?

a. It loads a backup configuration file from a TFTP server. b. It saves the new IOS to Flash memory. c. It reboots the router. d. It loads the new configuration file in NVRAM.

9. Which router command deletes the backup configuration file in NVRAM?

a. delete backup-config

b. erase backup-config

c. delete startup-config

d. erase startup-config


10. Which router command causes the router to reboot?

a. reload

b. restart

c. reboot

d. rerun

11. When is the router setup mode executed?

a. After the saved configuration file is loaded into main memory b. When the network administrator needs to enter complex protocol features

on the router c. When the router begins software initialization d. When the router cannot find a valid configuration file

12. Which of the following does not describe features of the router setup mode?

a. Many default settings appear in square brackets. b. The prompt and command for the setup mode are “router# setup”. c. The first line and title of the setup dialog is “System Configuration

Dialog”. d. Pressing the Return key cancels dialog prompts.

13. Which of the following correctly describes a procedure for setup of router global and interface parameters on a router?

a. A default parameter is shown in square brackets at every prompt. b. The router hostname must be set. c. An enable secret password can be set, but is not required. d. For each installed interface, a series of questions must be answered.

14. Which of the following does not correctly describe a procedure for setup of global and interface parameters on a router?

a. An enable secret password must be entered. b. A default parameter is shown in square brackets at every prompt. c. Configuration values that you have determined for the installed interfaces

are entered as parameters at the interface prompts. d. The router hostname must be set.


15. What information do you need to gather before starting a global or interface configuration session on a router?

a. Brand and model of router and type of networks the router connects to directly

b. IOS version and current register setting c. Which routing protocols will be needed, IP addresses of interface and

subnets, and which interfaces are being used d. IP addresses of neighboring routers, size of Flash memory

16. Which of the following correctly describes the router setup script review?

a. The setup command program displays the configuration that was created from your answers to the setup prompts.

b. The setup command program asks you whether you want to change any of your answers.

c. If you choose to use the displayed configuration, you select a location to save it to.

d. If you choose not to use the configuration, you must reboot the router.

17. Which of the following correctly describes the procedure for modifying the script displayed upon completion of the router configuration process?

a. The setup command program prompts you at each of the script lines as to whether you want to change your answers.

b. You choose not to accept the configuration and the router then reboots. c. You select the dialog lines that you want to change and the program then

prompts you again at those lines. d. The script tells you to use configuration mode to modify the configuration.

18. Why might you want to issue show startup-config and show running-config commands?

a. It’s time to update the IOS and you need to kill certain router processes before proceeding.

b. To determine the time since the router booted and the current register setting.

c. The router suddenly isn’t working right and you want to compare the initial state to the present state.

d. To find out where the IOS booted from and which version is being used.


19. Why should the enable password be different from the enable secret password?

a. The router asks that the passwords be changed monthly if they are the same.

b. To provide an additional category of users. c. The enable password can be read directly from the configuration file. d. The IOS behaves badly if they are the same.

20. What file(s) would you find in NVRAM?

a. IOS and configuration files b. Configuration file c. Backup copy of IOS d. Limited version IOS and Registry files


Chapter 20

Router Configuration 1

Introduction

The router uses information from the configuration file when it starts up. The configuration file contains commands to customize router operation. As you saw in the previous chapter, if no configuration file is available, the system configuration dialog setup guides you through creating one.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided. Configuration files can come from the console, NVRAM, or a TFTP server. The router has several modes:

• Privileged mode is used for copying and managing entire configuration files.

• Global configuration mode is used for one-line commands and commands that change the entire router.

• Other configuration modes are used for multiple command lines and detailed configurations.

The router provides a hostname, a banner, and interface descriptions to aid in identification.

• What does it mean to configure a router? Router configuration information can be generated by several means. You can use the privileged EXEC configure command to configure from a virtual (remote) terminal, a modem connection, or a console terminal. This enables you to enter changes to an existing configuration at any time. You can also use the privileged EXEC configure command to load a configuration from a network TFTP server, which enables you to maintain and store configuration information at a central site.

• Why must routers be configured? A router must know which interfaces are to be used, which routed and routing protocols are supported, along with security and access list configurations.


• Explain how to work with 11.x config files, compare and contrast router configuration modes, and prepare a flowchart of 11.x configuration methods. The commands shown in Figure 20-4 are used with Cisco IOS Release 11.0 and later. Figure 20-4 shows you a way to do the following:

⇒ Enter configuration statements.

⇒ Examine the changes you have made.

⇒ If necessary, modify or remove configuration statements.

⇒ Save the changes to a backup in NVRAM that the router uses when it starts up.


Define the following term as completely as you can. Use the online Chapter 20 or the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition, material for help.

Configure terminal Command used to configure manually from the console terminal.

Focus Questions

1. What does it mean to configure a router? Why must routers be configured?

Configuring a router usually describes the process by which a router learns its Layer 3 addresses, hostname, passwords, support protocols. A router must know which interfaces are to be used, which routed and routing protocols are supported, along with security and access list configurations.

2. The commands copy running-config tftp and copy running-config startup-config store the currently running configuration from RAM to _____ and _____, respectively.

A network TFTP server and NVRAM, respectively.

3. What do the prompts for user EXEC mode, privileged EXEC mode, and global configuration mode look like?

Router>, Router#, and Router(config)# 4. When configuring routers with Release 11.x methods, after you type show

running-config and display a desired configuration, what commands do you use to save changes to backup?

Use copy running-config startup-config and copy running-config tftp.


5. What are two basic tasks when first configuring a router?

Password configuration and naming the router (router identification configuration).



The following questions help you prepare for the CCNA Exam. Answers also appear in Appendix A, “Answers to the CCNA Exam Review Questions,” from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. Which of the following is not a function of the privileged EXEC configure command?

a. To configure a router from a virtual terminal b. To configure a TFTP server from a virtual terminal c. To configure a router from the console terminal d. To load a configuration from a network TFTP server

2. Which of the following is not a step in using the copy running-config tftp command to store the current router configuration? (The steps are listed in order.)

a. Enter the copy running-config tftp command. b. Enter the IP address of the router. c. Enter the name you want to assign to the configuration file. d. Confirm your choices.

3. Which of the following is not a step in using the copy tftp running-config command to load a router configuration file stored on a TFTP server? (The steps are listed in order.)

a. Enter the copy tftp running-config command. b. Select either a host configuration file or a network configuration file. c. Enter the IP address of the remote host from which you retrieve the

configuration file. d. Enter the name of the server to which you will load the file.

4. Which of the following does not correctly describe using a TFTP server to maintain router configuration files?

a. A host configuration file contains commands that apply to all routers and terminal servers on the network.

b. The convention for all filenames is UNIX-based. c. The default filename is hostname-config for the host file. d. Reconfiguration of the router occurs as soon as a new file is downloaded

to the router.


5. You want to replace your current configuration file with one located on a TFTP server, what is the process you need to go through to do this?

a. router (config)# copy tftp running-config Host or network configuration file [host]? IP address of remote host [255.255.255.255]? 131.108.6.155 Name of configuration file [Router-config]? paris.3 Configure using paris.3 from 131.108.6.155 [confirm] y Booting paris.3 from 131.108.6.155: !! [OK – 874/16000 bytes] Router (config)#

b. router # copy tftp running-config Host or network configuration file [host]? IP address of remote host [255.255.255.255]? 131.108.6.155 Configure using paris.3 from 131.108.6.155 [confirm] y Booting paris.3 from 131.108.6.155: !! [OK – 874/16000 bytes] Router#

c. router # copy tftp running-config Host or network configuration file [host]? Name of configuration file [Router-config]? paris.3 Configure using paris.3 from 131.108.6.155 [confirm] y Booting paris.3 from 131.108.6.155: !! [OK – 874/16000 bytes] Router#

d. router # copy tftp running-config Host or network configuration file [host]? IP address of remote host [255.255.255.255]? 131.108.6.155 Name of configuration file [Router-config]? paris.3 Configure using paris.3 from 131.108.6.155 [confirm] y Booting paris.3 from 131.108.6.155: !! [OK – 874/16000 bytes] Router#

6. What is the function of the configure memory router command?

a. Loads configuration information from NVRAM b. Erases the contents of NVRAM c. Stores into NVRAM the current configuration in RAM d. Displays the configuration saved in NVRAM

7. What is the function of the copy running-config startup-config router command?

a. Loads configuration information from NVRAM b. Erases the contents of NVRAM c. Stores into NVRAM the current configuration in RAM d. Displays the configuration saved in NVRAM


8. You added a new LAN onto you network; therefore, you updated your routing table and other parts of your configuration file. What command do you need to issue to save the new configuration file?

a. copy config startup-config

b. copy running-config startup-config

c. configure memory

d. copy startup-config config-running

9. Which router mode is a subset of the EXEC commands available at the privileged EXEC mode?

a. Global configuration mode b. User EXEC mode c. Interface configuration mode d. Router configuration mode

10. What is the system prompt for the user EXEC router mode?

a. Router>

b. Router#

c. Router(config)#

d. User EXEC

11. What happens when you type exit at a router mode prompt?

a. A configuration mode prompt appears. b. The router logs you off. c. The router backs out one mode level. d. A question prompt appears, requesting a network device location.

12. What does the router prompt look like when you are in global configuration mode?

a. Router#

b. Router (config-router)#

c. Router (config)#

d. Router-config#


13. If you want to back completely out of configuration mode, what must you enter?

a. exit

b. no config-mode c. Ctrl+E

d. Ctrl+Z 14. If you type Ctrl+Z to get out of configuration mode, where do you end up?

a. User EXEC mode b. Privileged EXEC mode c. Global configuration mode d. Router mode

15. If you are planning to configure an interface, what prompt should be on the router?

a. Router (config)#

b. Router (config-in)#

c. Router (config-intf)#

d. Router (Config-if)#

16. Which of the following does not describe a procedure for using the router global configuration mode?

a. You type configure to enter global configuration mode. b. You can specify the terminal, NVRAM, or a file on a server as the source

of configuration commands. c. You can type commands to configure specific interfaces. d. You can type a command to reach a prompt for the interface

configuration mode.

17. Which of the following is the system prompt for the global configuration mode?

a. Router#

b. Router(config)#

c. Router(config-global)#

d. Router(config-router)#


18. Which of the following does not describe a step in the procedure for using the router configuration mode?

a. Enter a global router protocol command type at the global configuration prompt.

b. The Router(config-router)# prompt indicates you are in router configuration mode.

c. Defaults can be selected for all available command options. d. Finish using this mode with the command exit.

19. Which of the following does not describe a step in the procedure for using the interface configuration mode?

a. Enter a global interface type and number command at the global configuration prompt.

b. The Router(config-if)# prompt indicates you are in interface configuration mode.

c. Interfaces can be turned on and off using commands in this mode. d. Interface types are enabled at subcommands in this mode.

20. Which of the following is a correct order for the process of configuring a router? (Assume you have already made router changes in configuration mode.)

a. Save changes to backup, decide whether changes are your intended results, examine results, and examine backup file.

b. Examine results, decide whether changes are your intended results, save changes to backup, and examine backup file.

c. Decide whether changes are your intended results, examine backup file, save changes to backup, and examine results.

d. Examine results, save changes to backup, decide whether changes are your intended results, examine backup file.

21. Which of the following best describes the process of configuring a router?

a. Examine results, make changes in configuration mode, remove changes, and decide whether changes are your intended results.

b. Decide if changes are your intended results, make changes in configuration mode, examine results, and remove changes.

c. Make changes in configuration mode, decide whether changes are your intended results, examine results, and remove changes.

d. Make changes in configuration mode, examine results, decide whether changes are your intended results, and remove changes.


22. Which of the following is a command that can be used to save router configuration changes to a backup?

a. Router# copy running-config tftp

b. Router# show running-config

c. Router# config mem

d. Router# copy tftp running-config

23. Which of the following is not a command to remove router configuration changes?

a. Router(config)# no ...

b. Router# config mem

c. Router# copy running-config startup-config

d. Router# copy tftp running-config

24. Which of the following correctly describes password configuration on routers?

a. All passwords are established in the privileged EXEC mode. b. All passwords alter the password character string. c. A password can be established on all incoming Telnet sessions. d. The enable password command restricts access to user EXEC mode.

25. Which of the following does not describe password configuration on routers?

a. Passwords can be established in every configuration mode. b. A password can be established on any console terminal. c. The enable secret password uses an encryption process to alter the

password character string. d. All password establishment begins in the global configuration mode.

26. When you are setting passwords for vty 0 4, for what access point to the router are you setting a password for?

a. Line consoles b. Telnet sessions c. Remote host router d. Virtual hosts


27. The password set up with the enable-secret command is to control direct access to what?

a. User EXEC mode b. Configure Interface mode c. Privilege EXEC mode d. Global configuration mode

28. Which of the following correctly describes procedures for confirming router identification?

a. Routers should be named only after initial testing of the network. b. If no name is configured, the system automatically assigns the router a

number. c. You name the router in global configuration mode. d. The login banner can be configured to display system error messages.

29. Which of the following does not describe procedures for confirming router identification?

a. If no name is configured, the system default router name is Router. b. Naming your router to be the host should be one of the first network

configuration tasks. c. The login banner is configured in global configuration mode. d. You can configure a message-of-the-day banner to display on specified

terminals.

30. You want to create a message to let people know a little something about the network when they log in—what command enables you to do this?

a. banner mesg

b. banner motd

c. daily mesg

d. daily motd


Chapter 21

IOS Images

Introduction

The default source for Cisco IOS software depends on the hardware platform; but most commonly, the router looks to the configuration commands saved in NVRAM. Cisco IOS software offers several alternatives. You can specify other sources where the router should look for software, or the router uses its own fallback sequence as necessary to load software. Settings in the configuration register enable alternatives for where the router will bootstrap Cisco IOS software. You can specify enabled configuration-mode boot system commands to enter fallback sources for the router to use in sequence. Save these statements in NVRAM to use during the next startup with the command copy running-config startup-config. The router uses these commands as needed, in sequence, when it restarts. If NVRAM lacks boot system commands the router can use, however, the system has its own fallback alternatives. The router falls back and uses default Cisco IOS in Flash memory. If Flash memory is empty, the router tries its next TFTP alternative. The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided. Routers boot Cisco IOS software from

⇒ Flash

⇒ TFTP server

⇒ ROM (not full Cisco IOS)

⇒ Multiple source options provide flexibility and fallback alternatives

• Why does the router need an operating system? The OS is a vital and necessary piece of the routing process. It creates the framework for which the entire routing process is based on. Different versions of software are necessary (based on the needed technologies and improvements made to the software).

• Why might there be different versions of router operating systems? Cisco products have expanded beyond the generic router to include many platforms at many points within the networking product spectrum. To optimize how Cisco IOS software operates on these various platforms, Cisco is working to develop many different Cisco IOS software images. These images accommodate the various platforms, available memory resources, and feature set needs that customers have for their network devices.


• Explain the process by which the router locates IOS software. The default source for Cisco IOS software startup depends on the hardware platform, but most commonly, the router looks to the boot system commands saved in NVRAM. However, Cisco IOS software does allow you to use several alternatives. You can specify other sources for the router to look for software, or the router can use its own fallback sequence, as necessary, to load the software.

• Explain the configuration register. The order in which the router looks for IOS images to load depends on the boot field setting in the configuration register. You can change the default configuration register setting with the global configuration command configregister. Use a hexadecimal number as the argument for this command as in the following example: Router# configure terminal

Router(config)# config-register 0x10F

• Compare and contrast the boot options for obtaining IOS: from Flash memory, from the network, and from ROM. ⇒ Set the configuration register value to 0x100 if you need to enter the

ROM monitor (primarily a programmer’s environment). From the ROM monitor, boot the operating system manually by using the b command at the ROM monitor prompt. (This sets the boot field bits to 0-0-0-0.)

⇒ Set the configuration register to 0x101 to configure the system to boot automatically from ROM. (This sets the boot field bits to 0-0-0-1.)

⇒ Set the configuration register to any value from 0x102 to 0x10F to configure the system to use the boot system commands in NVRAM. This is the default. (This sets the boot field bits to between 0-0-1-0 and 1-1-1-1.)

• Describe the show version command and all the information it tells you. The show version command displays information about the Cisco IOS software version that is currently running on the router. This includes the configuration register and the boot field setting. In the example illustrated in Listing 21-1, the Cisco IOS version and descriptive information is highlighted on the second output line. The screen captured shows an experimental version of Release 11.2. This line shows the system image name: System image file is "c4500-f-mz", booted via tftp from 171.69.1.129

In addition, the show version command displays information about the type of platform on which the version of Cisco IOS software is currently running.


• Describe the processes for creating a software image backup, upgrading the image from a network, and loading a software image backup. ⇒ Creating a software image backup: You should copy a system image back to a network server. This copy of the system image can serve as a backup copy. Figure 21-2 and Listing 21-2 use the show flash command to learn the name of the system image file (xk09140z), and the copy flash tftp command to copy the system image to a TFTP server. The files can be renamed during transfer.

⇒ The copy tftp flash command: After you have a backup copy of the current Cisco IOS software image, you can load a new image. You download the new image from the TFTP server by using the command copy tftp flash. Figure 21-3 and Listing 21-3 show that this command begins by requesting the IP address of the remote host that will act as the TFTP server. Next, the prompt asks for the filename of the new IOS image. You need to enter the correct filename of the update image (as it is named on the TFTP server).

⇒ How to load a software image backup: If you need to load the backup Cisco IOS version, again use the copy command copy tftp flash, which will enable you to download the image that you previously uploaded to the TFTP server. After you enter the copy tftp flash command, as shown in Listing 21-4, the system prompts you for the IP address (or name) of the TFTP server. This can be another router serving ROM or Flash software images. The system then prompts you for the filename of the software image.



Acknowledgment number Next expected TCP octet.

ARP (Address Resolution Protocol) Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.

Autonomous system Collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16-bit number by the IANA. Sometimes abbreviated AS.

Bandwidth The difference between the highest and lowest frequencies available for network signals. The term is also used to describe the rated throughput capacity of a given network medium or protocol.

Broadcast Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast address.


Checksum 1) Method for checking the integrity of transmitted data. A checksum is an integer value computed from a sequence of octets taken through a series of arithmetic operations. The value is recomputed at the receiving end and compared for verification. 2) Calculated checksum of the header and data fields. Configuration register In Cisco routers, a 16-bit, user-configurable value that determines how the router functions during initialization. The configuration register can be stored in hardware or software. In hardware, the bit position is set using a jumper. In software, the bit position is set by specifying a hexadecimal value using configuration commands.

Delay The time between the initiation of a transaction by a sender and the first response received by the sender. Also, the time required to move a packet from source to destination over a given path. Destination port Number of the called port. Distance-vector routing algorithm Class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree. Distance-vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance-vector routing algorithms can be prone to routing loops, but are computationally simpler than link-state routing algorithms.

DNS (Domain Name System) System used in the Internet for translating names of network nodes into addresses. Dynamic routing Routing that adjusts automatically to network topology or traffic changes.

EEPROM EPROM that can be erased using electrical signals applied to specific pins.

Enhanced IOS image that has additional capabilities and/or protocols usually identified by the word Plus or referred to as Feature Pack.

Flooding Traffic passing technique used by switches and bridges in which traffic received on an interface is sent out all of the interfaces of that device except the interface on which the information was originally received.

Flow control Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed.

Handshake Sequence of messages exchanged between two or more network devices to ensure transmission synchronization.

HLEN Number of 32-bit words in the header.

Host Computer system on a network. Similar to the term node except that host usually implies a computer system; whereas, node generally applies to any networked system, including access servers and routers.

IGRP (Interior Gateway Routing Protocol) IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks.


Link-state routing algorithm Routing algorithm in which each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. Link-state algorithms create a consistent view of the network and are therefore not prone to routing loops, but they achieve this at the cost of relatively greater computational difficulty and more widespread traffic (compared with distance-vector routing algorithms).

MTU (maximum transmission unit) Maximum packet size, in bytes, that a particular interface can handle.

Network 1) Collection of computers, printers, routers, switches, and other devices that can communicate with each other over some transmission medium. 2) Command that assigns a NIC-based address to which the router is directly connected. 3) Command that specifies any directly connected networks to be included.

OSPF (Open Shortest Path First) Link-state, hierarchical IGP routing algorithm proposed as a successor to RIP in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. Ping Short for Packet Internet Groper or Packet Internetwork Groper, a utility to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. Ping is used primarily to troubleshoot Internet connections.

RARP (Reverse Address Resolution Protocol) Protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses.

Reliability Ratio of expected to received keepalives from a link. If the ratio is high, the line is reliable. Used as a routing metric.

RIP (Routing Information Protocol) IGP supplied with UNIX BSD systems. The most common IGP in the Internet. RIP uses hop count as a routing metric.

Sequence number Number used to ensure correct sequencing of the arriving data. Source port Number of the calling port.

Static route Route that is explicitly configured and entered into the routing table. Static routes take precedence over routes chosen by dynamic routing protocols.

Subnetwork 1) In IP networks, a network sharing a particular subnet address. Subnetworks are networks arbitrarily segmented by a network administrator to provide a multilevel, hierarchical routing structure while shielding the subnetwork from the addressing complexity of attached networks. Sometimes called a subnet. 2) In OSI networks, a collection of ESs and ISs under the control of a single administrative domain and using a single network access protocol.

TCP (Transmission Control Protocol) Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack. Telnet Command used to verify the application layer software between source and destination stations. This is the most complete test mechanism available. Trace Command that uses Time-To-Live (TTL) values to generate messages from each router used along the path. This is very powerful in its capability to locate failures in the path from the source to the destination.



Window Number of octets that the receiver is willing to accept.


Focus Questions

1. Why does the router need an operating system? Why might there be different versions of router operating systems?

The OS is a vital and necessary piece of the routing process. It creates the framework for which the entire routing process is based on. Different versions of software are necessary (based on the needed technologies and improvements made to the software).

2. Routers can boot Cisco IOS software from where?

a. Flash memory b. A TFTP server c. Both a and b

3. The router cannot be configured to look elsewhere if the IOS software is not in Flash memory.

a. True b. False

4. The configuration register is an n-bit register in NVRAM. What is the value of n?

a. 8 b. 16 c. 32

5. What command would you use to check the configuration register setting?

a. configure terminal

b. config-register

c. show version


6. What does the first E in EEPROM stand for?

a. Erasable b. Electronically c. Enable




1. Which of the following correctly describes a method for specifying how a router loads the Cisco IOS software?

a. Designate fallback sources for the router to use in sequence from NVRAM

b. Configure the Cisco IOS software image for the location where it will bootstrap

c. Manually boot a default system image at a virtual terminal d. Manually boot a default system image at the network server

2. Which is the sequence used by the router for automatic fallback to locate Cisco IOS software?

a. Flash, NVRAM, TFTP server b. NVRAM, TFTP server, Flash c. NVRAM, Flash, TFTP server d. TFTP server, Flash, NVRAM

3. Which of the following does not describe configuration register settings for Cisco IOS bootstrapping?

a. The order in which the router looks for system bootstrap information depends on the boot field setting.

b. You change the configuration register setting with the command config-register.

c. You use a hexadecimal number when setting the configuration register boot field.

d. Use the show running-config command to check the boot field setting.

4. Which of the following is information displayed by the Cisco IOS show version command?

a. Statistics about the router’s memory b. Name of the system image c. Information about the Flash memory device d. Status of configured network protocols


5. Which command is used to discover the configuration register setting?

a. show register

b. show running-config

c. show version

d. show startup-config

6. Which of the following does not correctly describe a fallback option for booting Cisco IOS software?

a. Flash memory provides storage that is not vulnerable to network failures. b. Loading Cisco IOS software from a TFTP server is a good option in case

Flash memory becomes corrupted. c. The system image booted from ROM is usually a complete copy of Cisco

IOS software. d. ROM might contain an older version of Cisco IOS software.

7. Which of the following correctly describes preparing to use a TFTP server to copy software to Flash memory?

a. The TFTP server must be another router or a host system such as a UNIX workstation or a laptop computer.

b. The TFTP host must be a system connected to an Ethernet network. c. The name of the router containing the Flash memory must be identified. d. The Flash memory must be enabled.

8. Which of the following is not a step in preparing to copy software from a TFTP host to Flash memory?

a. Check the router to make sure you can see and write into Flash. b. Verify that the router has sufficient room to accommodate Cisco IOS

software. c. Use the show ip route command to make sure you can access the

TFTP server over the TCP/IP network. d. Check the TFTP server to make sure you know the file or file space for

the Cisco IOS software image.


9. Which of the following does not describe the procedure to verify sufficient room in Flash memory for copying software?

a. Use the show flash command. b. Identify the total memory in Flash, which is the available memory. c. Compare the available memory with the length of the Cisco IOS software

image to be copied. d. If there is not enough available memory, you can try to obtain a smaller

Cisco IOS software image.

10. How would you determine the size of the IOS image file on a TFTP server?

a. Go to the Cisco web site and consult the image file size table. b. Type show version on your router. c. Do dir or ls on the TFTP server. d. Telnet to the TFTP server and issue a show files command.

11. Which of the following is the fastest way to make sure the TFTP server is reachable prior to trying to transfer an IOS image file?

a. Trace the TFTP server. b. Ping the TFTP server. c. Telnet to the TFTP server. d. Call the TFTP server administrator.

12. Why do you need to determine the file size of the IOS image on the TFTP server before transferring it to your router?

a. To check that there is enough space in Flash to store the file b. To verify that the file is the correct IOS for your router c. To complete a trivial file transfer protocol operation, the file size must be

known d. To calculate the download time for the file and thus, the amount of time

the router will be out of service

13. What information is not provided in the Cisco image filename system?

a. Capabilities of the image b. The platform on which the image runs c. Where the image runs d. Size of the image


14. Which of the following is not part of the procedure for creating a Cisco IOS software image backup to a TFTP server?

a. Use the show flash command to learn the name of the system image file.

b. Enter the copy flash tftp command to begin the copy process. c. Enter the IP address of the router holding the image file. d. You can rename the file during transfer.

15. Why does an administrator create a Cisco IOS software image backup?

a. To verify that the copy in Flash is the same as the copy in ROM b. To provide a fallback copy of the current image prior to copying the

image to a new router c. To create a fallback copy of the current image as part of procedures

during recovery from system failure d. To create a fallback copy of the current image prior to updating with a

new version

16. Which of the following is not part of the procedure for loading a new Cisco IOS software image to Flash memory from a TFTP server? (The procedures are listed in correct order.)

a. Backup a copy of the current software image to the TFTP server. b. Enter the copy flash tftp command to download the new image

from the server. c. The procedure asks if you are willing to erase Flash. d. A series of Vs on the display indicates successful check run verification.

17. Which of the following is not part of the procedure for loading a backup Cisco IOS software image to Flash memory from a TFTP server? (The procedures are listed in correct order.)

a. Enter the copy tftp flash command. b. A prompt asks you for the IP address of the TFTP server. c. If a file with the same name exists in Flash memory, the file being copied

automatically replaces it. d. Enter the reload command to boot up the router using the newly copied

image.


18. What is the initial boot attempt if the router register is set to Ox2100?

a. ROM monitor b. TFTP server c. ROM d. Flash






Chapter 22

Router Configuration 2

Introduction

One way to begin understanding the way the Internet works is to configure a router. It is also one of the primary topics on the CCNA exam, and one of the most important and sought-after skills of employers. Routers are complex devices that can have a wide variety of possible configurations.

Concept Questions

• What does it mean to configure a router? Router configuration information can be generated by several means. You can use the privileged EXEC configure command to configure from a virtual (remote) terminal, a modem connection, or a console terminal. This enables you to enter changes to an existing configuration at any time. You can also use the privileged EXEC configure command to load a configuration from a network TFTP server, which enables you to maintain and store configuration information at a central site.

• Why must routers be configured? A router must know which interfaces are to be used, which routed and routing protocols are supported, along with security and access list configurations.

• Describe the router configuration process. You can configure a router from many external locations, including the following:

⇒ From the console terminal (a computer connected to the router through a console port) during its installation

⇒ Via a modem by using the auxiliary port

⇒ From virtual terminals, after the router has been installed on the network

⇒ From a TFTP server on the network


• Explain the router password recovery procedure on 1600 and 2500 series routers. Step-by-step procedure (1600 Router): Step 2. Attach a terminal or PC with terminal emulation to the console port of

the router. Use the following terminal settings: 9600 baud rate No parity 8 data bits 1 stop bit No flow control

Step 6. If you still have access to the router, type show version and record the setting of the configuration register; it is usually 0x2102 or 0x102.

Step 7. If you don't have access to the router (because of a lost login or TACACS password), you can safely consider that your configuration register is set to 0x2102.

Step 8. Using the power switch, turn off the router and then turn it back on.

Step 9. Press Break on the terminal keyboard within 60 seconds of the power up to put the router into ROMMON.

Step 10. Type confreg 0x2142 at the rommon 1> prompt to boot from Flash without loading the configuration.

Step 11. Type reset at the rommon 2> prompt.

The router reboots but ignores its saved configuration. Step 12. Type no after each setup question or press Ctrl+C to skip the initial

setup procedure.

Step 13. Type enable at the Router> prompt.

You'll be in enable mode and see the Router# prompt. Step 14. Important: Type config mem or copy start running to copy the

nonvolatile RAM (NVRAM) into memory. Do not type config term.

Step 15. Type wr term or show running.

The show running and wr term commands show the configuration of the router. In this configuration you see under all the interfaces the shutdown command, which means all interfaces are currently shutdown. Also, you can see the passwords either in encrypted or unencrypted format.

Step 16. Type config term and make the changes.

The prompt is now hostname(config)#.


Step 17. Type enable secret password.

Step 18. Issue the no shutdown command on every interface that is used. If you issue a show ip interface brief command, every interface that you want to use should be "up up".

Step 19. Type config-register 0x2102 or the value you recorded in step 2.

Step 20. Press Ctrl+Z to leave the configuration mode.

The prompt is now hostname#. Step 21. Type write mem or copy running startup to commit the

changes.

Step-by-step procedure (2500 Router): Step 1. Attach a terminal or PC with terminal emulation to the console port of

the router. Use the following terminal settings: 9600 baud rate No parity 8 data bits 1 stop bit No flow control

Step 2. Using the power switch, turn the router off and then turn it back on.

Step 3. Press Break on the terminal keyboard within 60 seconds of the power-up to put the router into ROMMON.

Step 4. Type o at the > prompt and record the current value of the configuration register (usually 0x2102, or 0x102):

>o

Configuration register = 0x2102 at last boot

Bit# Configuration register option settings:

15 Diagnostic mode disabled

Step 5. Type o/r 0x2142 at the > prompt to boot from Flash without loading the configuration.

Step 6. Type i at the > prompt.

The router reboots, but ignores its saved configuration. Step 7. Type no after each setup question or press Ctrl+C to skip the initial setup

procedure.

Step 8. Type enable at the Router> prompt.

You'll be in enable mode and see the Router# prompt.


Step 9. Important: Type config mem or copy start running to copy the nonvolatile RAM (NVRAM) into memory. Do not type config term.

Step 10. Type wr term or show running.

The show running and wr term commands show the configuration of the router. In this configuration, you see under all the interfaces the shutdown command, which means all interfaces are currently shut down. Also, you can see the passwords either in encrypted or unencrypted format.

Step 11. Type config term and make the changes.

The prompt is now hostname(config)#.

Step 12. Type enable secret password.

Step 13. Issue the no shutdown command on every interface that is used. If you issue a show ip interface brief command, every interface that you want to use should be "up up".

Step 14. Type config-register 0x2102 or the value you recorded in step 4.

Step 15. Press Ctrl+Z to leave the configuration mode.

The prompt is now hostname#. Step 16. Type write mem or copy running startup to commit the

changes.




1. What are the major elements of a typical router configuration?

a. Passwords; interfaces; routing protocols; DNS b. Boot sequence; interfaces; tftp server; NVRAM c. NVRAM; ROM; DRAM; interfaces d. Interfaces; routing protocols; configuration register; flash

2. In a password recovery procedure, immediately after issuing a Ctrl+Break upon router startup, what should be the configuration register setting?

a. 0x2102 b. 0x2142 c. 0x0000 d. 0x10F

3. In a password recovery procedure, just before saving the running configuration and after you enable a new secret password, what should be the configuration register setting?

a. 0x2102 b. 0x2142 c. 0x0000 d. 0x10F


4. What is the correct syntax to enable RIP on router A in the lab topology?

a. config t router rip int e0 ip address 192.5.5.1 255.255.255.0 no shutdown description this is the first Ethernet Interface CNTRL/Z copy run start

b.

config t router rip network 192.5.5.0 network 205.7.5.0 network 201.100.11.0 CNTRL/Z copy run start

c.

config t router rip ip host LAB-A 192.5.5.1 207.5.1 201.100.11.1 ip host LAB-B 201.100.11.2 219.17.100.1 199.6.13.1 ip host LAB-C 199.6.13.2 223.8.151.1 204.204.7.1 ip host LAB-D 204.204.7.2 210.93.105.1 ip host LAB-E 210.93.105.2

d. CNTRL/Z copy run start

e. None of the above


5. What is the correct syntax for completely configuring Ethernet and serial interfaces?

a. config t int e0 ip host LAB-A 192.5.5.1 207.5.1 201.100.11.1 ip host LAB-B 201.100.11.2 219.17.100.1 199.6.13.1 ip host LAB-C 199.6.13.2 223.8.151.1 204.204.7.1 ip host LAB-D 204.204.7.2 210.93.105.1 ip host LAB-E 210.93.105.2 CNTRL/Z copy run start

b.

config t int e0 network 192.5.5.0 network 205.7.5.0 network 201.100.11.0

c. CNTRL/Z copy run start

d. config t int e0 ip address 192.5.5.1 255.255.255.0 no shutdown description this is the first Ethernet Interface CNTRL/Z copy run start

e. None of the above


Chapter 23

TCP/IP

Introduction

The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols was developed as part of the research done by the Defense Advanced Research Projects Agency (DARPA). Later, TCP/IP was included with the Berkeley Software Distribution of UNIX. The Internet protocols can be used to communicate across any set of interconnected networks. They are equally well suited for both LAN and WAN communication. The IP suite includes not only Layer 3 and Layer 4 specifications (such as IP and TCP), but also specifications for such common applications as e-mail, remote login, terminal emulation, and file transfer.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided. The TCP/IP protocol stack has the following components:

⇒ Protocols to support file transfer, e-mail, remote login, and other applications.

⇒ Reliable and unreliable transports.

⇒ Connectionless datagram delivery at the network layer ICMP provides control and message functions at the network layer.

• The TCP/IP protocol stack maps closely to the lower layers of the OSI reference model. What function do the application protocols perform? ⇒ They provide services to application processes that are outside of the

OSI model. ⇒ They identify and establish the availability of intended communication

partners. ⇒ They synchronize cooperating applications. ⇒ They establish agreement on procedures for error recovery and control of

data integrity.


• The transport layer performs two functions. What are they? The transport layer enables a user’s device to segment data from several upper-layer applications for placement on the same Layer 4 data stream, and enables a receiving device to reassemble the upper-layer application segments. The Layer 4 data stream is a logical connection between the endpoints of a network; it provides transport services from a source host to a destination host. This service is sometimes referred to as an end-to-end service.

• What kind of protocol is TCP? TCP is a connection-oriented, reliable protocol that provides flow control by providing sliding windows and offers reliability by providing sequence numbers and acknowledgments. TCP resends anything that is not acknowledged and supplies a virtual circuit between end-user applications. The advantage of TCP is that it provides guaranteed delivery of segments.



Acknowledgment number Next expected TCP octet. ARP (Address Resolution Protocol) Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.

Checksum 1) Method for checking the integrity of transmitted data. A checksum is an integer value computed from a sequence of octets taken through a series of arithmetic operations. The value is recomputed at the receiving end and compared for verification. 2) Calculated checksum of the header and data fields.

Destination port Number of the called port.

Flow control Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed.

Handshake Sequence of messages exchanged between two or more network devices to ensure transmission synchronization.

HLEN Number of 32-bit words in the header.

RARP (Reverse Address Resolution Protocol) Protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses.

Sequence number Number used to ensure correct sequencing of the arriving data. Source port Number of the calling port.

TCP (Transmission Control Protocol) Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack.



Window Number of octets that the receiver is willing to accept.


Focus Questions

1. How do the TCP/IP conceptual layers relate to the OSI layers?

OSI TCP/IP Application ! Application Presentation Session Transport ! Transport Network ! Internet Data Link ! Network Interface Physical

2. Compare and contrast TCP and UDP.

TCP is a connection-oriented, reliable protocol that provides flow control by providing sliding windows and offers reliability by providing sequence numbers and acknowledgments. TCP resends anything that is not acknowledged and supplies a virtual circuit between end-user applications. The advantage of TCP is that it provides guaranteed delivery of segments UDP is a connectionless and unreliable protocol that is responsible for transmitting messages but provides no software checking for segment delivery. The advantage that UDP provides is speed. Because UDP provides no acknowledgments, less control traffic is sent across the network, making the transfer faster.


3. Briefly describe everything you know about the fields in a TCP segment.

The TCP segment contains the following fields:

Source Port—The number of the source (port) for this segment.

Destination port—The number of the destination (port) for this segment.

Sequence Number—The number used to ensure correct sequencing of the arriving data. It is the number assigned to the first octet in the user data field.

Acknowledgment Number—The next expected TCP octet.

HLEN—The number of 32-bit words in the header.

Reserved—Set to 0.

Code Bits—The control functions (for example, setup and termination of a session).

Window—The number of octets that the sender is willing to accept.

Checksum—The calculated checksum of the header and data fields.

Urgent Pointer—Indicator of the end of the urgent data.

Option—One currently defined: maximum TCP segment size.

Data—Upper-layer protocol data.

4. Briefly describe everything you know about the fields in an IP datagram.

The fields in this IP datagram are as follows:

VES—Version number

HLEN—Header length, in 32-bit words

Type of Service—How the datagram should be handled

Total Length—Total length (header + data)

Identification, Flags, Frag Offset—Provides fragmentation of datagrams to allow differing MTUs in the internetwork

TTL—Time-To-Live

Protocol—The upper-layer (Layer 4) protocol sending and receiving the datagram

Header Checksum—In integrity check on the header

Source IP Address and Destination IP Address—32-bit IP addresses

IP Options—Network testing, debugging, security, and other options


5. Briefly distinguish between IP, ICMP, ARP, and RARP.

IP serves as a protocol for many of the services used on the Internet today, such as SMTP, HTTP, DNS, Telnet, and so on. ICMP provides control and message functions at the network layer. ICMP is implemented by all TCP/IP hosts. ARP is used to resolve or map a known IP address to a MAC sublayer address to allow communication on a multi-access medium, such as Ethernet. RARP is the reverse of ARP and is used to resolve or map a known MAC sublayer address to an IP address.




1. Which of the following best describes TCP/IP?

a. Suite of protocols that can be used to communicate across any set of interconnected networks

b. Suite of protocols that allows LANs to connect into WANs c. Protocols that allow for data transmission across a multitude of networks d. Protocols that allow different devices to be shared by interconnected

networks

2. Which of the following best describes the purpose of TCP/IP protocol stacks?

a. Maps closely to the OSI reference model in the upper layers b. Supports all standard physical and data-link protocols c. Transfers information in a sequence of datagrams d. Reassembles datagrams into complete messages at the receiving

location

3. The function of the application layer of the TCP/IP conceptual layers is best described by which of the following?

a. Responsible for breaking messages into segments and then reassembling them at the destination

b. Acts as a protocol to manage networking applications c. Exists for file transfer, e-mail, remote login, and network management d. Resends anything that is not received, and reassembles messages from

the segments

4. Why are TCP three-way handshake/open connections used?

a. To ensure that lost data can be recovered if problems occur later b. To determine how much data the receiving station can accept at one time c. To provide more efficient use of bandwidth by users d. To change binary ping responses into information in the upper layers


5. What does a TCP sliding window do?

a. It makes the window larger so more data can come through at once, which results in more efficient use of bandwidth.

b. The window size slides to each section of the datagram to receive data, which results in more efficient use of bandwidth.

c. It allows the window size to be negotiated dynamically during the TCP session, which results in more efficient use of bandwidth.

d. It limits the incoming data so that each segment must be sent one by one, which is an inefficient use of bandwidth.

6. What do the TCP sequence and acknowledgment numbers do?

a. They break datagrams into their binary coefficients, number them sequentially, and send them to their destination, where the sender acknowledges their receipt.

b. They break messages down into datagrams that are numbered and then sent to a host according to the sequence set by the source TCP.

c. They provide a system for sequencing datagrams at the source and acknowledging them at the destination.

d. They provide sequencing of segments with a forward reference acknowledgment, number datagrams before transmission, and reassemble the segments into a complete message.

7. Why does UDP use application layer protocols to provide reliability?

a. To speed up transmission over the network. b. The lack of reliability protocols makes the software less expensive and

easier to configure. c. It lacks a protocol to sequence datagrams and negotiate window size. d. It does not use windowing or acknowledgements.

8. What does the acronym ICMP stand for?

a. Internetwork Connection Model Protocol b. Internet Connection Monitor Protocol c. Internet Control Message Protocol d. Internetwork Control Mode Protocol


9. What is the purpose of ICMPs?

a. They put the internetwork in control mode so that protocols can be set up.

b. They are messages that the network uses to monitor connection protocols.

c. They are standard binary messages that act as model internetwork protocols.

d. They are messages carried in IP datagrams used to send error and control messages.

10. What does the acronym ARP stand for?

a. Address Resource Protocol b. Address Resolution Protocol c. Address Research Program d. Address Routing Program

11. What is the function of ARP?

a. It completes research for a destination address for a datagram. b. It is used to develop a cached address resource table. c. It is used to map an IP address to a MAC address. d. It sends a broadcast message looking for the router address.

12. How does a sender find out the destination’s MAC address?

a. It consults its routing table. b. It sends a message to all the addresses searching for the address. c. It sends out a broadcast message to the entire LAN. d. It sends out a broadcast message to the entire network.

13. What is the function of the RARP?

a. It is a protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses.

b. It is a protocol used to map a 32-bit IP address to a MAC address. c. It is a protocol used to develop a cached address resource table for the

router. d. It a protocol that completes research for a destination address for a

datagram based on the IP address.


14. Which of the following best describes the purpose of checksum?

a. Method for comparing IP addresses against those permitted access to allow entry by a host

b. Method for checking the integrity of transmitted data c. Method for computing a sequence of octets taken through a series of

arithmetic operations d. Method for recomputing IP address values at the receiving end and

comparing them for verification

15. Which of the following best describes flow control?

a. A device at the destination side that controls the flow of incoming data b. A buffer at the source side that monitors the outflow of data c. A technique that ensures that the source does not overwhelm the

destination with data d. A suspension of transmission until the data in the source buffers has

been processed

16. What does the acronym SNMP stand for?

a. Standard Node Monitor Protocol b. Standard Network Management Protocol c. Simple Node Management Protocol d. Simple Network Management Protocol

17. What is the purpose of SNMP?

a. Means to monitor and control network devices and to manage configurations, statistics collection, performance, and security

b. Means to monitor the devices that are connected to one router, and assign a regular address to each host on the node network

c. Protocol that provides the network administrator with the ability to manage the devices on the network and control who has access to each node

d. Protocol that allows for the management of network security, performance, and configuration from a remote host

18. Which of the following best describes TTL?

a. Field in the datagram header that determines how long the data is valid b. Field in an IP header that indicates how long a packet is considered valid c. Field within an IP datagram that indicates the upper-layer protocol

sending the datagram d. Field in a datagram head that indicates when the next data packet will

arrive


19. Which of the following best describes UDP?

a. A protocol that acknowledges flawed or intact datagrams b. A protocol that detects errors and requests retransmissions from the

source c. A protocol that processes datagrams and requests retransmissions when

necessary d. A protocol that exchanges datagrams without acknowledgments or

guaranteed delivery

20. Which of the following best describes window size?

a. The maximum size of the window that a software can have and still process data rapidly

b. The number of messages that can be transmitted while awaiting an acknowledgment

c. The size of the window, in picas, that must be set ahead of time so data can be sent

d. The size of the window opening on a monitor, which is not always equal to the monitor size


Chapter 24

IP Addressing

Introduction

In a TCP/IP environment, end stations communicate with servers or other end stations. This occurs because each node using the TCP/IP protocol suite has a unique 32-bit logical address. This address is known as the IP address. Each company listed on the internetwork is seen as a single unique network that must be reached before an individual host within that company can be contacted. Each company network has an address; the hosts that live on that network share that same network address, but each host is identified by the unique host address on the network.

Concept Questions


• IP addresses are specified in 32-bit dotted-decimal format. Explain how to develop an IP address. Each node using the TCP/IP protocol suite has a unique 32-bit logical address. This address is specified in 32-bit dotted-decimal format. The IP address is almost always accompanied by the subnet mask, also in 32-bit dotted-decimal format. The subnet mask indicates which of the 32 bits in the IP address are used for network representation and which bits are used for host representation. The network bits are assigned by InterNIC or ARIN. The host bits are determined by you, the network administrator.

• Router interfaces can be configured with an IP address.

• ping and trace commands can be used to verify IP address configuration. • What actually happens when you issue a ping command? Explain verbally

and with a sketch. The ping command sends a packet to the destination host and then waits for a reply packet from that host. Results from this echo protocol can help evaluate the path-to-host reliability, identify delays over the path, and determine whether the host can be reached or is functioning. Student sketch should be similar to that of Figure 18-11.




Broadcast Data packet that will be sent to all nodes on a network. Broadcasts are identified by a broadcast address.

DNS (Domain Name System) System used in the Internet for translating names of network nodes into addresses. Flooding Traffic-passing technique used by switches and bridges in which traffic received on an interface is sent out all of the interfaces of that device except the interface on which the information was originally received.

Host Computer system on a network. Similar to the term node except that host usually implies a computer system; whereas, node generally applies to any networked system, including access servers and routers. Network 1) Collection of computers, printers, routers, switches, and other devices that are able to communicate with each other over some transmission medium. 2) Command that assigns a NIC-based address to which the router is directly connected. 3) Command that specifies any directly connected networks to be included.

Ping (Packet Internet Groper) An ICMP echo message and its reply. Often used in IP networks to test the reachability of a network device. Subnetwork 1) In IP networks, a network sharing a particular subnet address. Subnetworks are networks arbitrarily segmented by a network administrator to provide a multilevel, hierarchical routing structure while shielding the subnetwork from the addressing complexity of attached networks. Sometimes called a subnet. 2) In OSI networks, a collection of ESs and ISs under the control of a single administrative domain and using a single network access protocol. Telnet A standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854. Trace Command that uses Time-To-Live (TTL) values to generate messages from each router used along the path. This is very powerful in its capability to locate failures in the path from the source to the destination.


Focus Questions

1. If a router has a serial interface S0 with IP address 172.16.1.2, an Ethernet interface E0 with IP address 172.31.4.1, and a Token Ring interface T0 with an IP address of 172.31.16.1, and if all interfaces use a mask of 255.255.255.0, find the subnet (wire) number for each interface.

S0 – 172.16.1.0 E0 – 172.31.4.0 T0 – 172.31.16.0

2. What is the result of the command Router (config-if)# ip address ip-address subnet-mask?

The command assigns an address and a subnet mask and binds the TCP/IP stack to this physical or logical interface. Now the interface/subinterface can transmit and receive datagrams.

3. What does the ip host command do?

The ip host command makes a static name-to-address entry in the router’s configuration file.

4. What type of information is obtained from the show hosts command?

The show hosts command is used to display a cached list of hostnames and addresses.

5. Distinguish among the three commands that enable you to verify address configuration in your internetwork. .

Three commands enable you to verify address configuration in your internetwork: telnet—Verifies the application layer software between source and destination stations. This command is the most complete testing mechanism available. ping—Uses the ICMP protocol to verify the hardware connection and the logical address at the Internet layer. This command is a very basic testing mechanism and is the most common means of testing IP connectivity. trace—Uses TTL values to generate messages from each router used along the path. This command is very powerful in its capability to locate failures in the path from the source to the destination.




1. How does a router dynamically gain access to IP addresses?

a. All host addresses must be entered individually by the network administrator.

b. The router learns addresses from other routers. c. The network administrator creates a routing table of all addresses. d. All hosts automatically send their address to any available router.

2. What kind of address can a device or interface have?

a. Any kind b. A network number and then all ones c. A nonzero network number d. Neither a network nor broadcast number

3. If a router has an Ethernet interface E0, with IP address 172.31.4.1, and if the interface uses a mask of 255.255.255.0, what is the subnet number?

a. E0: 172.16.1.0 b. E0: 172.31.4.0 c. E0: 172.31.16.0 d. E0: 172.31.41.0

4. If you wanted to assign an address and a subnet mask and start IP processing on an interface, what command would you use?

a. IP address subnet mask b. IP address c. Subnet mask d. Address IP process

5. If you want to connect a name to an IP address, such as asu 129.219.0.0, what command structure would you use?

a. ip host asu 129.219.0.0

b. ip name asu 129.219.0.0

c. ip host name asu 129.219.0.0

d. ip host address asu 129.219.0.0


6. What is the purpose of tcp-port-number in the ip host commands?

a. It identifies which IP address to use when using the hostname with an EXEC connect or telnet command.

b. It sets the default port of any device to port 23. c. It sets the port of the source device in the router table. d. It identifies which TCP port to use when using the hostname with an

EXEC connect or telnet command.

7. What is the purpose of the ip name-server command?

a. It defines which hosts can provide the name service. b. It defines a naming scheme that allows a device to be identified by its

location. c. It identifies which TCP port to use when using the hostname. d. It generates messages from each router used along a datagram’s path.

8. Which of the following best describes the function of the show hosts command?

a. It identifies the subnet mask being used at the destination site. b. It maintains a cache of host name-to-address mappings for use by EXEC

commands. c. It is used to display a cached list of host names and addresses. d. It shows the hostname for the IP address.

9. When you use the ping command and get a result of !, what does it mean?

a. Successful receipt of an echo reply b. Times out waiting for datagram reply c. Destination unreachable error d. Congestion-experienced packet

10. What does it mean when you use the ping command and get a result of . ?

a. Successful receipt of an echo reply b. Timed out waiting for datagram reply c. Destination unreachable error d. Congestion-experienced packet


11. When you use the ping command and get a result of U, what does it mean?

a. Timed out waiting for datagram reply b. Destination unreachable error c. Congestion-experienced packet d. Ping interrupted

12. When you use the ping command and get a result of C, what does it mean?

a. Packet Time-To-Live exceeded b. Ping interrupted c. Destination unreachable error d. Congestion-experienced packet

13. When you use the ping command and get a result of I, what does it mean?

a. Destination unreachable error b. Ping interrupted c. Congestion-experienced packet d. Packet type unknown

14. When you use the ping command and get a result of ?, what does it mean?

a. Packet Time-To-Live exceeded b. Ping interrupted c. Packet type unknown d. Congestion-experienced packet

15. When you use the ping command and get a result of &, what does it mean?

a. Congestion-experienced packet b. Ping interrupted c. Packet type unknown d. Packet Time-To-Live exceeded

16. Which of the following best describes the function of the extended command mode of the ping command?

a. Used to specify the supported Internet header options b. Used to specify the time frame for the ping return c. Used to diagnose why aping was delayed or not returned


d. Used to trace the datagram as it passes through each router

17. How do you enter the extended mode of the ping command?

a. ping x

b. ping e

c. ping [Return key] d. ping m

18. What does the response !H mean, when it comes in response to the trace command?

a. The probe was received by the router, but was not forwarded. b. The protocol was unreachable and the trace was terminated. c. The network was unreachable, but the last router was up. d. The port was reached, but the wire to the network was malfunctioning.

19. When it comes in response to the trace command, what does the response P mean?

a. Time out. b. The port was unreachable. c. The protocol was unreachable. d. The network was unreachable.

20. What does the response N mean, when it comes in response to the trace command?

a. The name has no IP address connected to it. b. The probe was not received, so it could not be forwarded. c. The protocol was unreachable. d. The network was unreachable.

21. When it comes in response to the trace command, what does the response U mean?

a. The address was unreachable. e. The protocol was unreachable. f. The network was unreachable. g. The port was unreachable.


22. What does the response * mean when it comes in response to the trace command?

a. The destination device refused the trace. b. The trace timed out. c. The network refused the trace. d. The source used a trace that was not supported by the network protocol.


Chapter 25

Routing

Introduction

Which path should traffic take through the cloud of networks? Path determination occurs at Layer 3 of the OSI reference model, the network layer. The path determination function enables a router to evaluate the available paths to a destination and to establish the preferred handling of a packet. Routing services use network topology information when evaluating network paths. This information can be configured by the network administrator or collected through dynamic processes running in the network. The network layer interfaces to networks and provides best-effort, end-to-end packet delivery services to its user, the transport layer. The network layer sends packets from the source network to the destination network based on the IP routing table. After the router determines which path to use, it proceeds with forwarding the packet: It takes the packet it accepted on one interface and forwards it to another interface or port that reflects the best path to the packet’s destination.

Concept Questions

Demonstrate you knowledge of these concepts by answering the following questions in the space provided.

• Internetworking functions of the network layer include network addressing and best path selection for traffic. What is best-path selection? The network layer uses the IP routing table to send packets from the source network to the destination network. After the router determines which path to use, it proceeds with forwarding the packet. It takes the packet that it accepted on one interface and forwards it to another interface or port that reflects the best path to the packet’s destination.

• In network addressing, one part of the address is used to identify the path used by the router and the other is used for ports or devices on the network. Which part of the address is used to identify the path used by the router? The router uses the network portion of the address to make path selections to pass the packet to the next router along the path.


• Routed protocols allow routers to direct user traffic, and routing protocols work between routers to maintain path tables. Explain this key difference. Routed protocol—Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme. Routed protocols define the field formats within a packet. Packets are generally conveyed from end system to end system. A routed protocol uses the routing table to forward packets. The Internet Protocol (IP) is an example of a routed protocol.

Routing protocol—Support a routed protocol by providing mechanisms for sharing routing information. Routing protocol messages move between the routers. A routing protocol allows the routers to communicate with other routers to update and maintain tables. TCP/IP examples of routing protocols include the following:

⇒ Routing Information Protocol (RIP)

⇒ Interior Gateway Routing Protocol (IGRP)

⇒ Enhanced Interior Gateway Routing Protocol (EIGRP)

⇒ Open Shortest Path First (OSPF)

• Network discovery for distance-vector routing involves exchange of routing tables; problems can include slow convergence. What other problems can occur as a result of exchanging routing tables? Routing loops can occur if a network’s slow convergence on a new configuration causes inconsistent routing entries.

• For link-state routing, routers calculate the shortest paths to other routers; problems can include inconsistent updates. What other problems might occur with link-state routing? Two link-state concerns exist: processing and memory requirements, and bandwidth requirements

• Balanced hybrid routing uses attributes of both link-state and distance-vector routing, and can apply paths to several protocols. What advantages does balance hybrid routing offer? Balanced hybrid routing protocols use distance vectors with more accurate metrics to determine the best paths to destination networks. However, they differ from most distance-vector protocols by using topology changes to trigger routing database updates. The balanced hybrid routing protocol converges rapidly, like the link-state protocols.



Define the following terms as completely as you can. Use the online Chapter 25 or the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition material for help.

Default route Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table.

Delay The time between the initiation of a transaction by a sender and the first response received by the sender. Also the time required to move a packet from source to destination over a given path.

Dynamic routing Routing that adjusts automatically to network topology or traffic changes. Also called adaptive routing.

Enhanced IGRP (EIGRP) Advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance-vector protocols.

Header Control information placed before data when encapsulating that data for network transmission.

Hop count Routing metric used to measure the distance between a source and a destination. RIP uses hop count as its sole metric.

Hop Term describing the passage of a data packet between two network nodes (for example, between two routers).

IGRP (Interior Gateway Routing Protocol) IGRP was developed by Cisco to address the problems associated with routing in large, heterogeneous networks.

OSPF (Open Shortest Path First) Link-state, hierarchical IGP routing algorithm proposed as a successor to RIP in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. OSPF was derived from an early version of the ISIS protocol.

RIP (Routing Information Protocol) IGP supplied with UNIX BSD systems. The most common IGP in the Internet. RIP uses hop count as a routing metric.

Routing metric Method by which a routing algorithm determines that one route is better than another. This information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop count, load, MTU, path cost, and reliability. Sometimes referred to simply as a metric.

Routing protocol Protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols include IGRP, OSPF, and RIP.


Stub network Network that has only a single connection to a router.


Focus Questions

1. What does a router do? What improvements do network addresses offer over physical addresses?

Routers are internetworking devices that operate at OSI Layer 3 (the network layer). They tie together, or interconnect, network segments or entire networks, as shown in Figure 10-3. They pass data packets between networks based on Layer 3 information. Network addresses have logical or hierarchical addresses, which allows for the grouping of end stations into such things as departments, floors, or buildings.

2. Distinguish between routed protocols and routing protocols.

Routed protocols are used between router to direct user traffic. Any network protocol that provides enough information in its network layer address to be forwarded from host to host based on the addressing scheme is a routed protocol. The most relevant example for this discussion is IP. Routing protocols are used only between routers to maintain routing tables. Examples are RIP and IGRP. Routing protocols support routed protocols by providing a mechanism for sharing routing information messages among routers.

3. How does multiprotocol routing enable the Internet to exist?

There are many different host systems all over the world, with many different routed protocols. Multiprotocol routing—by which a router can pass traffic from Novell, Apple, DEC, IP and many other networks—allows these diverse hosts to communicate.

4. List and briefly describe at least five examples of routing metrics.

The metrics most commonly used by routers include the following:

Bandwidth—The data capacity of a link

Delay—Length of time required to move a packet from source to destination

Load—Amount of activity on a network resource such as a router or a link

Reliability—Usually refers to the error rate of each network link

Hop count—Number of passages of a packet through the output port of one router

Ticks—Delay on a data link using IBM PC clock ticks

Cost—Arbitrary value, usually based on bandwidth or other measurements, that is assigned by the network administrator

5. Briefly describe distance-vector routing.

Distance vector-based routing algorithms pass periodic copies of a routing table from router to routers; each router receives a routing table from its direct neighbors.



The following questions help review for the CCNA exam. Answers also appear in Appendix A, “Answers to the CCNA Exam Review Questions,” from the Cisco Networking Academy Program: Engineering Journal and Workbook, Volume I, Second Edition.

1. What function allows routers to evaluate available routes to a destination and to establish the preferred handling of a packet?

a. Data linkage b. Path determination c. SDLC interface protocol d. Frame Relay

2. What information is used by routing services to evaluate network paths?

a. MAC addresses b. Name server tables c. Network topology d. ARP requests

3. Where can routing services obtain the network topology information needed to evaluate network paths?

a. From RARP and ARP tables b. From network name servers c. From bridges talking to routers during messaging sessions d. From information collected by dynamic processes

4. What two functions does a router use to relay packets from one data link to another?

a. Link-state testing and convergence b. Convergence and switching c. Path determination and link-state testing d. Path determination and switching

5. How does the network layer send packets from the source to the destination?

a. Uses an IP routing table b. Uses ARP responses c. Refers to a name server d. Refers to the bridge


6. What happens at the router during a switching operation?

a. The router changes from link-state to distance-vector mode. b. A packet accepted on one interface is forwarded to another interface or

port that reflects the best path to the destination. c. A test message is sent over the proposed route to make sure it is

operational. d. The received packet has the header stripped, read, and a new header

attached listing the next stop on the route.

7. Why is it important to prevent unnecessary broadcasts over the entire internetwork?

a. Broadcasts incur processing overhead and waste network capacity. b. Broadcasts cannot be sent as multiphase transmissions, so routers must

change modes to deal with them. c. Broadcasts are common causes of collisions and should be avoided

whenever possible. d. Broadcasts can quickly relay bad routing tables throughout an

internetwork.

8. How does the network layer avoid unnecessary broadcast messages?

a. By using error-trapping algorithms b. By using consistent end-to-end addressing c. By using name servers to do look-up functions d. By using link-state detection

9. What problem for the network layer does using consistent end-to-end addressing solve?

a. Reduces chance of infinite loops b. Avoids split horizons c. Avoids unnecessary broadcast messages d. Reduces count to infinity problems

10. What are the two parts of an address that routers use to forward traffic through a network?

a. Network address and host address b. Network address and MAC address c. Host address and MAC address d. MAC address and subnet mask


11. Which network device uses the network address to define a path?

a. Bridge b. Router c. Hub d. Server

12. How does a router make path selections?

a. By looking at the network portion of the address b. By looking at the host portion of the address c. By looking at mean distances between routers d. By looking at the port or device on the network

13. What does the host address specify?

a. Type of device b. Distance to the nearest network hub c. Specific port or device on the network d. Network the device is on

14. How does the host portion of an address help a router in its path determination function?

a. Defines a path through the network b. Contains distance information that can be used to calculate the shortest

route c. Refers to a specific port on the router that leads to an adjacent router in

that direction d. Tells the router the type of device and its distance from the router

15. What does the switching function of a router do?

a. Allows greater throughput and capacity by multitasking b. Allows the router to accept a packet on one interface and forward it on

another interface c. Exchanges the old header of a data packet for a new header that

includes path information for the next router d. Changes the router from receive and send mode to broadcast mode

when part of the network fails


16. Which best describes a routed protocol?

a. Provides enough information to allow a packet to be forwarded from host to host

b. Provides information necessary to pass data packets up to the next highest network layer

c. Allows routers to communicate with other routers to maintain and update address tables

d. Allows routers to bind MAC and IP address together

17. Which is an example of a routed protocol?

a. RIP b. IP c. IGRP d. OSPF

18. Which best describes a routed protocol?

a. Passes data packets up to the next highest network layer b. Binds MAC and IP addresses together c. Defines the format and use of fields within a packet d. Exchanges routing tables and shares routing information between routers

19. Which best describes a routing protocol?

a. Provides information to allow a packet to be forwarded from host to host b. Binds MAC and IP addresses together c. Defines the format and use of fields within a data packet d. Allows routers to communicate with other routers to maintain and update

address tables

20. Which best describes a routing protocol?

a. A protocol that accomplishes routing through the implementation of an algorithm

b. A protocol that specifies how and when MAC and IP addresses are bound together

c. A protocol that defines the format and use of fields within a data packet d. A protocol that allows a packet to be forwarded from host to host


21. Which best describes the difference between a routed versus a routing protocol?

a. Routed protocols are used between routers to maintain tables; whereas, routing protocols are used between routers to direct traffic.

b. Routed protocols use distance-vector algorithms; whereas, routing protocols use link-state algorithms.

c. Routed protocols are used between routers to direct traffic; whereas, routing protocols used between routers to maintain tables.

d. Routed protocols use dynamic addressing; whereas, routing protocols use static addressing.

22. What happens when a data-link frame is received on a router interface?

a. The packet header is removed and a new one with additional routing information is attached.

b. A frame header is sent to check the path integrity prior to sending the packet on towards its destination.

c. The packet is sent to the nearest bridge that forwards it to the next router or the final destination.

d. The header is examined to determine the destination network and consults the routing table to see which outgoing interface is associated with that network.

23. What happens after a router has matched the destination network with an outgoing interface?

a. The packet is sent to the nearest bridge that forwards it to the next router or the final destination.

b. A frame header is sent to check the path integrity prior to sending the packet on towards its destination.

c. The packet is queued for delivery to the next hop in the path. d. The packet header is removed and a new one with additional routing

information is attached.

24. Which of the following best describes a data-link frame header?

a. Controls information placed in front of data when it is readied for network transmission

b. Broadcasts message sent over the network to warn routers of network failures in specific links

c. Diagnostic message used to check network links for problems d. Packets sent by routers to other routers to update routing tables


25. What is the control information placed in front of data in a data packet called?

a. Addressing b. Header c. Trailer d. Encapsulate

26. Which of the following best describes a hop?

a. Passage of a data packet between two routers b. Device which connects two or more networks together c. Shortest distance between source and destination d. Exchange and copying of ARP tables between two noncontiguous

network devices

27. What is the passage of a data packet between two routers called?

a. Exchange b. Hop c. Transmittal d. Signaling

28. Which best describes multiprotocol routing?

a. Capability to send packets simultaneously out different ports b. Capability to shift from static to dynamic routing as network loads change c. Capability to maintain routing tables for several routed protocols

concurrently d. Capability to rewrite frame headers to formats compatible with different

networks

29. What does multiprotocol routing allow routers to do?

a. Rewrite frame headers to formats compatible with different networks b. Shift from static to dynamic routing as network loads change c. Send packets simultaneously out different ports d. Deliver packets from several routed protocols over the same data links


30. Which best describes static routing?

a. A route that is manually entered into a routing table by the network administrator

b. A route received from the local name server c. A route that is automatically entered into a routing table d. An optimum route between devices as determined by the RARP table

31. Which best describes dynamic routing?

a. Automatic updating of routing tables whenever new information is received from the internetwork

b. Manual entry of data into a routing table by the network administrator c. Following preset paths from device to device d. RARP server determines optimum route between devices and copies

those routes into a routing table

32. What type of routing occurs without the intervention of a network administrator?

a. Default b. Dynamic c. Progressive d. Static

33. What is one advantage of static routing?

a. More secure as parts of an internetwork can be hidden b. Requires little active management by the network administrator c. Adjusts automatically to topology or traffic changes d. Can compensate for router failures by using alternate paths

34. What is one advantage for using static routing on a stub network?

a. Compensates for route failures by using alternative paths b. Requires little active management by the network administrator c. Adjusts automatically to topology or traffic changes d. Avoids the network overhead required by dynamic routing

35. What are the two major classes of routing algorithms?

a. Checksum and link state b. Checksum and traffic load c. Distance vector and traffic load d. Distance vector and link state


36. Which best describes a distance-vector protocol?

a. Determines the direction and distance to any link in the internetwork b. Each router maintains a complex database of internetwork topology

information c. Computationally rather complex d. Method of routing which prevents loops and minimizes counting to infinity

37. What do distance-vector algorithms require of routers?

a. Default routes for major internetwork nodes in case of corrupted routing tables

b. Send its entire routing table in each update to its neighbors c. Fast response times and ample memory d. Maintain a complex database of internetwork topology information

38. Why is it important in distance-vector algorithms for routers to send copies of their routing table to neighboring routers?

a. To prevent error propagation b. To stop routing loops c. To enable split horizon mapping d. To communicate topology changes quickly

39. What is a major drawback of distance-vector algorithms?

a. More network traffic b. Computationally difficult c. Prone to routing loops d. Cannot implement hold-down timers

40. What is one disadvantage of distance-vector algorithms?

a. Routers do not know the exact topology of an internetwork, only distances between points

b. More network traffic c. Computationally difficult d. Cannot implement hold-down timers

41. What is one advantage of distance-vector algorithms?

a. Not likely to count to infinity b. Implements easily on very large networks c. Not prone to routing loops d. Computationally simpler


42. Which of the following best describes link-state algorithms?

a. Re-create the exact topology of the entire internetwork b. Require minimal computations c. Determine distance and direction to any link on the internetwork d. Use little network overhead and reduces overall traffic

43. Which of the following best describes link-state algorithms?

a. Use little network overhead and reduces overall traffic b. Each router broadcasts information about the network to all nodes on the

network c. Determine distance and direction to any link on the internetwork d. Use a great deal of network overhead and increase overall traffic

44. What is true about link-state routing algorithms?

a. Require more network traffic than distance-vector algorithms b. Computationally rather simple c. Require less router memory and slower response times d. Maintain full knowledge of distant routers and how they interconnect

45. Which best describes convergence?

a. When messages simultaneously reach a router and a collision occurs b. When several routers simultaneously route packets along the same path c. When all routers in an internetwork have the same knowledge of the

structure and topology of the internetwork d. When several messages are being sent to the same destination

46. Which term is used to describe an internetwork state when all routers have the same knowledge of the structure and topology of the internetwork?

a. Congruence b. Equivalence c. Correspondence d. Convergence

47. Why is fast convergence a desirable attribute of a routing protocol?

a. Reduces time period over which routers make incorrect routing decisions b. Reduces network traffic c. Reduces routing loop time d. Reduces memory requirements of local routers


48. After a network topology change, what routing protocol characteristic reduces incorrect or wasteful routing decisions?

a. Symmetry b. Convergence c. Equivalence d. Correspondence

49. What is a routing loop?

a. A route to often requested destinations b. A network path that is circular and has no branches c. A packet that cycles repeatedly through a constant series of network

nodes d. A process that routers go through when performing self-diagnostics

50. What is the process called where packets never reach their destination, but instead cycle repeatedly through the same series of network nodes?

a. Split horizon b. End-to-end messaging c. Convergence d. Routing loop

51. Why do routing loops occur?

a. Slow convergence after a modification to the internetwork. b. Split horizons are artificially created. c. Network segments fail catastrophically and take other network segments

down in a cascade effect. d. Default routes were never established and initiated by the network

administrator.

52. Why do routing loops occur?

a. Split horizons are artificially created. b. A network device fails and that information is slowly passed to all the

routers in the internetwork. c. Default routes were never established and initiated by the network

administrator. d. Network segments fail catastrophically and take other network segments

down in a cascade effect.


53. Why does the problem of counting to infinity occur?

a. Split horizon b. Noncongruence c. Slow convergence d. Router inequivalence

54. Which best describes the count-to-infinity problem?

a. Routers continuously increment the hop count as a routing loop proceeds.

b. Packets cycle repeatedly through a constant series of network nodes. c. During heavy traffic periods, freak collisions can occur and damage the

packet headers. d. After a split horizon occurs, two sets of metrics exist for the same

destination and neither matches that in the routing table.

55. How can the count-to-infinity problem be prevented?

a. By forcing a routing loop b. By invoking a split horizon process c. By tracking network traffic levels and regulating flow d. By imposing an arbitrary hop-count limit

56. How can the count-to-infinity problem be solved?

a. Initiate a routing loop b. Define infinity as some maximum number c. Switch from distance-vector to link-state mode d. Force a router convergence and reconciliation

57. What happens when the hop-count exceeds the maximum in a routing loop?

a. The loop ends and the data packet is returned to the source for retransmission later.

b. The default route is recalled and used. c. The network is considered unreachable, and the loop ends. d. A count to infinity is initiated, and a split horizon invoked.


58. How can the count to infinity problem be prevented?

a. By using routing loops b. By using split horizon routing systems c. By increasing router memory d. By using hold-down timers

59. Which best describes hold-down timers?

a. Timer that synchronizes the router table update process b. Time during which messages are held if network segment is temporarily

unavailable c. Time allowed before intervention to halt routing loop d. Time during which routers will neither send nor receive updated routing

tables

60. Why are hold-down timers useful?

a. They flush bad information about a route from all routers in the network. b. They force all routers in a segment to synchronize switching operations. c. They reduce the amount of network traffic during high traffic periods. d. They provide a mechanism for bypassing failed sections of network.

61. When are routers placed in a hold-down state?

a. When a routing loop occurs b. When a link in a route fails c. When a routing table becomes corrupted d. When convergence occurs too slowly

62. How does a hold-down timer work?

a. By holding messages in routing loops for a given time period, the hold-down timer reduces network traffic at peak times.

b. When the hop count exceeds a fixed value, the hold-down timer holds the message until a split horizon is established.

c. When a router receives an update indicating that a network is now inaccessible, the router marks the route and starts a hold-down timer.

d. When a count is started, a hold-down timer is started too; if after a given time period the count continues, the timer halts the process and returns control to the nearest router.


63. What are the major two link-state concerns?

a. Split horizons and convergence b. Processing and memory requirements c. Routing loops and equivalence d. Table copying and counting to infinity

64. Which of the following best describes link-state advertisement (LSA)?

a. Broadcast message in response to a convergence call b. Broadcast message relaying state of data links (up or down) to all routers c. Broadcast packet that contains information about neighbors and path

costs d. Broadcast packet that is initiated by an active routing loop

65. What are LSAs used for?

a. To halt routing loops b. To determine path metrics c. To broadcast convergence calls d. To maintain routing tables of receiving routers

66. What is the most complex and important aspect of link-state routing?

a. Making sure all routers get all the necessary LSA packets b. Ensuring that convergence occurs rapidly c. Avoiding routing loops during initial start up d. Providing mechanisms for split horizons and count to infinity avoidance

67. What will happen if routers have different sets of LSAs?

a. A check sum procedure is initiated and faulty routing tables repaired. b. Routes become unreachable because routers disagree about a link. c. A master comparison is forced and subsequent convergence on a single

routing table occurs. d. A broadcast message is sent with the master copy of the routing table to

all routers.


68. What is one problem with link-state updating?

a. Easy to start a routing loop and subsequent count to infinity b. Routers can become unreachable because they don’t have a complete

picture of the internetwork c. In synchronizing large networks, it is difficult to tell which updates are

correct d. If the master routing table is corrupted, the entire network will go down

69. What is one problem with link-state updating?

a. Routers can become unreachable because they don’t have a complete picture of the internetwork.

b. Easy to start a routing loop and subsequent count to infinity. c. If the master routing table is corrupted, the entire network will go down. d. Order of router startup alters the topology learned.

70. Which of the following is correct?

a. Distance-vector routing gets all topological data from the routing tables of their neighbors; whereas, link-state routing develops a map of the network by accumulating LSAs.

b. Distance-vector routing develops a map of the network; whereas, link-state routing gets topological data from the routing tables of their neighbors.

c. Distance-vector routing requires lots of bandwidth and network overhead; whereas, link-state routing requires considerably less.

d. Distance-vector routing has quick convergence time; whereas, link-state routing has a slow convergence time and is therefore prone to routing loops.


a. Distance-vector routing requires lots of bandwidth and network overhead; whereas, link-state routing requires considerably less.

b. Distance-vector routing determines the best path by adding to the metric value it receives; whereas, link-state routing has the routers calculating their own shortest path to destinations.

c. Distance-vector routing has quick convergence time; whereas, link-state routing has a slow convergence time and is therefore prone to routing loops.

d. Distance-vector routing has the routers calculate their own shortest path to destinations; whereas, link-state routing determines the best path by adding to the metric value it receives from its neighbors.



a. Distance-vector routing has a quick convergence time; whereas, link-state routing has a slow convergence time and is therefore prone to routing loops.

b. Distance-vector routing requires lots of bandwidth and network overhead; whereas, link-state routing requires considerably less.

c. Distance-vector routing updates for topology changes with periodic table updates; whereas, link-state routing updates are triggered by topology changes.

d. Distance-vector routing updates are triggered by topology changes; whereas, link-state routing updates for topology changes with periodic scheduled table updates.

73. Which best describes hybrid routing?

a. Uses distance vectors to determine best paths, but topology changes trigger routing table updates

b. Uses distance-vector routing to determine best paths between topology during high-traffic periods

c. Uses topology to determine best paths but does frequent routing table updates

d. Uses topology to determine best paths but uses distance vectors to circumvent inactive network links


Chapter 26

Routing Protocols

Introduction

After testing the hardware and loading the Cisco IOS system image, the router finds and applies the configuration statements. These entries provide the router with details about router-specific attributes, protocol functions, and interface addresses. If the router faces a beginning condition where the router is unable to locate a valid startup-config file, however, it enters an initial router configuration mode called the setup mode. With the setup-mode command facility, you can answer questions in the system configuration dialog. This facility prompts you for basic configuration information. The answers you enter enable the router to use a sufficient, but minimal, feature router configuration, which includes the following:

• An inventory of interfaces

• An opportunity to enter global parameters

• An opportunity to enter interface parameters

• A setup script review

• An opportunity to indicate whether you want the router to use this configuration After you approve setup-mode entries, the router uses the entries as a running configuration. The router also stores the configuration in NVRAM as a new startup-config. You can start using the router. For additional protocol and interface changes, use the enable mode and enter the command configure.

Concept Questions


• Routers can be configured to use one or more IP routing protocols. Identify and briefly explain the different IP routing protocols. At the Internet layer of the TCP/IP suite of protocols, a router can use an IP routing protocol to accomplish routing through the implementation of a specific routing algorithm. Examples of IP routing protocols include the following:

RIP—A distance-vector routing protocol

IGRP—Cisco’s distance-vector routing protocol

OSPF—A link-state routing protocol

EIGRP—A balanced hybrid routing protocol


• Two IP routing protocols are RIP and IGRP. Compare and contrast these two IP routing protocols. RIP was originally specified in RFC 1058. Its key characteristics include the following: It is a distance-vector routing protocol. Hop count is used as the metric for path selection (see Figure 26-8). If the hop count is greater than 15, the packet is discarded. By default, routing updates are broadcast every 30 seconds. IGRP is a distance-vector routing protocol developed by Cisco. IGRP sends routing updates at 90-second intervals, advertising networks for a particular autonomous system. Some of the IGRP key design characteristics emphasize the following: Versatility that enables it to automatically handle indefinite, complex topologies Flexibility for segments that have different bandwidth and delay characteristics Scalability for functioning in very large networks


Define the following terms as completely as you can. Use the online Chapter 26 or the Cisco Systems Networking Academy: First-Year Companion Guide, Second Edition material for help.

Autonomous system Collection of networks under a common administration sharing a common routing strategy. Autonomous systems are subdivided by areas. An autonomous system must be assigned a unique 16-bit number by the IANA. Sometimes abbreviated AS.

Bandwidth The difference between the highest and lowest frequencies available for network signals. The term is also used to describe the rated throughput capacity of a given network medium or protocol.

Delay The time between the initiation of a transaction by a sender and the first response received by the sender. Also, the time required to move a packet from source to destination over a given path.

Distance-vector routing algorithm Class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree. Distance-vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance-vector routing algorithms can be prone to routing loops, but are computationally simpler than link-state routing algorithms. Also called Bellman-Ford routing algorithm.

Dynamic routing Routing that adjusts automatically to network topology or traffic changes. Also called adaptive routing.

Enhanced IGRP (EIGRP) Advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance-vector protocols. Compare with IGRP.


IGRP (Interior Gateway Routing Protocol) IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks. Compare with EIGRP. See also IGP, OSPF, and RIP.

Link-state routing algorithm Routing algorithm in which each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes in the internetwork. Link-state algorithms create a consistent view of the network and are therefore not prone to routing loops, but they achieve this at the cost of relatively greater computational difficulty and more widespread traffic (compared with distance-vector routing algorithms).

MTU ( maximum transmission unit) Maximum packet size, in bytes that a particular interface can handle.

OSPF (Open Shortest Path First) Link-state, hierarchical IGP routing algorithm proposed as a successor to RIP in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. OSPF was derived from an early version of the IS-IS protocol.

Reliability Ratio of expected to received keepalives from a link. If the ratio is high, the line is reliable. Used as a routing metric.

RIP (Routing Information Protocol) IGP supplied with UNIX BSD systems. The most common IGP in the Internet, RIP uses hop count as a routing metric.


Focus Questions

1. Default routes are manually defined by the system administrator as the route to take when no route to the destination is known. They are also known as which of the following?

a. Dynamic routes b. Default subnet c. Default network

2. Default routes are configured by using the ___________ command, while in the _____________ prompt.

a. ip default route; Router (config)#

b. ip default-network; Router (config)# c. ip default-route; Router(config-if)#


3. Which of the following are used to communicate within a given autonomous system?

a. Routing Information Protocols b. Exterior Routing Protocols c. Interior Routing Protocols

4. Routing protocols can be configured on a router while in which of the following modes?

a. Router#

b. Router(config)# d. Router(config-if)#

5. Which of the following protocols sends updated routing table information onto the network every 90 seconds?

a. IGRP b. RIP c. Exterior Gateway Protocol (EGP)



The following questions help you review for the CCNA exam. Answers also appear in Appendix A, “Answers to the CCNA Exam Review Questions,” from the Cisco Networking Academy Program: First-Year Companion Guide, Second Edition.

1. If you start the router and it cannot find Cisco IOS system image, what happens?

a. The router will not operate. b. The router will request that you make the Cisco IOS available. c. By default the router will start up in setup mode. d. The router will ask you to install any router operating system.

2. What command do you use to access the setup mode?

a. define b. exec c. setup d. configure

3. If you manually set up the router, what type of configuration will it have?

a. It will be fully configured. b. It will be minimally configured. c. You will only be able to use it to install Cisco IOS. d. It will be configured in such a way that no changes can be made, except

manually.

4. What kind of entries does a router initially refer to?

a. Entries about networks or subnets that are directly connected b. Entries it has learned about from the Cisco IOS software c. Entries whose IP address and mask information are known d. Entries it has learned about from other routers

5. Which of the following best describes a static route?

a. Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table

b. Route that is explicitly configured and entered into the routing table and takes precedence over routes chosen by dynamic routing protocols

c. Route that adjusts automatically to network topology or traffic changes d. Route that adjusts involuntarily to direct frames within a network topology


6. Which of the following best describes a dynamic routing?

a. Routing that is explicitly configured and entered into the routing table b. Routing that is used to direct frames for which a next hop is not explicitly

listed in the routing table c. Routing that adjusts automatically to network topology or traffic changes d. Routing that adjusts involuntarily to direct frames within a network

topology

7. What do link-state algorithms require routers to do?

a. Flood routing information about the state of its own links to all nodes on the internetwork

b. Flood all its routing information to all nodes on the internetwork c. Send a complete picture of the topology of the entire network to all nodes

on the network d. Base routing table on information provided by the every other router and

send IP information to all nodes on the network

8. An administrative distance of 15 would indicate which of the following?

a. The IP address is static. b. The IP address is dynamic. c. The routing information source is trustworthy. d. The routing information source is untrustworthy.

9. Why are routing updates not sent to a link if it is only defined by a static route?

a. Because each node in the network already knows the route b. To conserve bandwidth c. To keep routing tables small d. To keep routing tables organized

10. In the following command, what does the last number stand for?

router (config)# ip route 2.0.0.0 255.0.0.0 1.0.0.2 5

a. The number of hops b. The number of routes to the destination c. The administrative distance d. The destinations reference number in the routing table


11. Why would you set the administrative distance really high?

a. The network uses Enhanced IGRP. b. The dynamic address may be better. c. The network uses OSPF. d. The network uses only uses default network addresses.

12. Which of following is the correct syntax when configuring a static route with an administrative distance of five?

a. router (config)> ip route 2.0.0.0 255.0.0.0 1.0.0.2 5

b. router (config)# ip route 2.0.0.0 255.0.0.0 1.0.0.2 5

c. router (config)# ip route 2.0.0.0 1.0.0.2 5

d. router (config)# ip route 2.0.0.0 255.0.0.0 1.0.0.2


Chapter 27

Network Troubleshooting

Introduction

Troubleshooting tools that you might use for the software (IOS) include ping, trace ip route, telnet, and show arp.

Concept Questions

Demonstrate your knowledge of these concepts by answering the following questions in the space provided. • Describe typical Layer 1 errors.

Layer 1 errors can include the following (see Figure 27-2):

⇒ Broken cables

⇒ Disconnected cables

⇒ Cables connected to the wrong ports

⇒ Intermittent cable connections

⇒ Cables incorrectly terminated

⇒ Wrong cables used for the tasks at hand (must use cross-connects, rollovers, and straight-through cables correctly)

⇒ Transceiver problems

⇒ DCE cable problems

⇒ DTE cable problems

⇒ Devices powered off

• Describe typical Layer 2 errors. Layer 2 errors can include the following (see Figure 27-3):

⇒ Improperly configured serial interfaces

⇒ Improperly configured Ethernet interfaces

⇒ Incorrect clock rate settings on serial interfaces

⇒ Improper encapsulation set on serial interfaces (HDLC is default)

⇒ Faulty NIC


• Describe typical Layer 3 errors. Layer 3 errors can include these (see Figure 27-4):

⇒ Routing protocol not enabled

⇒ Wrong routing protocol enabled

⇒ Incorrect network/IP addresses

⇒ Incorrect subnet masks

⇒ Incorrect interface addresses

⇒ Incorrect DNS-to-IP bindings (host table entries)

⇒ Wrong autonomous system number for IGRP

• Describe some network troubleshooting strategies. It’s useful to have a general method to refer to when troubleshooting computer networks. This section outlines one such method used by many networking professionals. The steps are as follows: Step 1. Define the problem. What are the symptoms and the potential

causes? Step 2. Gather the facts. Isolate the possible causes.

Step 3. Consider the possibilities. Based on the facts gathered, narrow the focus to areas relevant to the specific problem. This is the step where you set the boundaries for the problem.

Step 4. Create an action plan. Devise a plan in which you manipulate only one variable at a time.

Step 5. Implement the action plan. Perform each step carefully while testing to see whether the symptom disappears.

Step 6. Observe the results. Determine whether you resolved the problem. If so, the process is complete.

Step 7. Repeat the process. If you did not resolve the problem, move to the next most likely cause on your list. Return to step 4, and repeat the process until you solve the problem.

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