Cisco CCNA 1 & 2 Notes

Physical Connection – A physical connection to a network is made by connecting a specialized expansion card.

Logical Connection – The logical connection uses standards called protocol. Protocols are formal description of a set of rules and conventions that govern how devices on a network communicate.

Transmission Control Protocol/Internet Protocol [TCP/IP] suite is the primary protocol used on the Internet. Suite of protocols that work together to send and receive data.

Applications that interprets the data and displays the information in a comprehensible format is the last part of the connection.

A web browser displays HTML as a web page. Also use proprietary plug in applications to display special data types such as video, audio, and animations.

File Transfer Protocol [FTP] is used to download files and programs from the Internet. Electronic components are unique in that they are designed to conduct or transmit data or signals in electronic form.

Transistors are devices that amplifies a signal or opens and closes a circuit. Micro processors can have millions of transistors.

Integrated circuit [IC] are devices that is made of semiconductor material. It contains many transistors and performs a specific task.

Resistor are devices that is made of material that opposes the flow of electric current.

Capacitor is an electronic component that stores energy in the form of an electrostatic field. It consists of two conducting metal plates separated by an insulating material.

Connector are ports or interfaces that cables plugs into. Examples include serial, parallel, USB, and disk drive interfaces.

Light Emitting Diode [LED] are semiconductor devices emitting light when a current passes through it. Commonly used as indicator lights.

PC components are typically though of as packaged or add on parts that provide additional functionality to a PC.

Printed Circuit Board [PCB] are thin plates on which chips [integrated circuits] and other components are placed. Examples include the motherboard and various expansion adapters.

Bus is a collection of circuits through which data is transmitted from one part of a computer to another. The bus 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.

Random Access Memory [RAM] also known as read write memory. Main working area used by the CPU for most processing and operations. Requires electrical power to maintain data storage.

Read Only Memory is a type of computer memory in which data has been prerecorded. After data has been written onto a ROM chip, it cannot be removed and can only read. A version of ROM known as EEPROM [Electronically Erasable Programmable Read Only Memory] can be written to it. Called Flash memory or Firmware. The basic input/output system [BIOS] in most PC s is stored in EEPROM.

Expansion slots located on laptops are called PCMIA, better known as the Personal Computer Memory Card International Association.

NIC is a printed circuit board that provides network communication capabilities to and from a PC. Better known as a LAN or Local Area Network.

NIC communicates with the network through a cable and with computer.

When NIC is installed into the computer, it requires an interrupt request [IRQ] for service from the CPU as well as an input/output [I/O] address, a memory space for the operating system [such as Linux or Windows], and drivers to perform its function.

A IRQ or Interrupt Request is a signal that informs a CPU that an event needing its attention has occurred. Sent over hardware line to the microprocessor.

When selecting a NIC for a network, consider the following:

1) Type of network. [Ethernet LAN*, Token Ring and Fiber Distributed Data Interface [FDDI]]2) Type of Medium [Coaxial*, Twisted Pair, Fiber Optic, or Wireless] 3) Type of System Bus [PCI* or ISA]

[* means more common or rare]

Modem is a electronic device that is used for computer communication through telephone lines. Allows data transfer between one computer and another over Public Switched Telephone Network [PSTN].

The term modem derives from the function of this device. The process of converting digital signals to analog and back again is called modulation/demodulation [hence the term modem].

Modems can be installed internally or attached to the computer by via a serial or USB interface externally.

Modems connect a computer to the network by dialing the telephone number of another computer's modem, typically that of the Internet Service Provider [ISP].

The NIC lets hosts connect to the network since it is considered the key component.

Situations that require NIC installation includes the following:1) Adding a NIC to a PC that does not already have one.2) Replacing a bad or damaged NIC.3) Upgrading from a 10 Mbps NIC to a 10/100 Mbps NIC.

To install a NIC, the user needs the following resources:1) Knowledge of how the adapter is configured, including jumpers and are plug and play software.2) Use of network card diagnostics including vendor supplied diagnostics and loopback test [see

the card's documentation]3) The ability to resolve hardware resource conflicts, including IRQ, I/O base address, and Direct

Memory Address [DMA], which is used to transfer data from RAM to a device without going through the CPU.

TCP/IP is a set of protocols or rules developed to allow cooperating computers to share resources across a network.

A computer must be running the TCP/IP protocol suite to access the Internet.

The PC requires an IP address, subnet mask, default gateway, DNS [Domain Name Server] information. This information for the PC to communicate across the network can be assigned manually or obtain automatically from a Dynamic Host Configuration Protocol [DHCP] server.

Information necessary to configure TCP/IP on a computer is typically obtained from the network administrator or an ISP.

Ping is a program that is useful for verifying a successful TCP/IP installation. Ping stands for Packet Internet Groper.

Following is some usages of the ping command: Ping 127.0.0.1 [internal loopback test]: Verifies the operation of the TCP/IP stack and NIC

transmit/receive function. Ping IP address of host computer: Verifies the TCP/IP address configuration for the local host. Ping default-gateway IP address: Verifies whether the router that connects the local network to

other networks can be accessed. Ping remote destination IP address: Verifies connectivity to a remote host.

A web browser acts on a users behalf by1) Contacting a web server2) Requesting Information3) Receiving Information4) Displaying the results on the screen

A web browser is software that interprets Hyper Text Markup Language [HTML], one of the languages to code web page content.

Other languages such as SGML and XML provide more advanced features for creating dynamic and interactive web pages than HTML does.

HTML most common markup language can display graphics, and play sounds, movies, and other multimedia files.

Hyperlinks are computer program commands that point to other HTML files on a web server or other places in the same document, which provide shortcuts to other web pages and files.Computers are electromechanical devices made up of electronic switches.

These impulses are understood by the computer as either on or off states [1s or 0s].

Computers work with and store data using electronic switches that are either on or off.

These 1s and 0s represent the two possible states of the electronic component in the computer and are binary digits or bits.

The American Standard Code for Information Interchange [ASCII], the most commonly used code for representing alphanumeric data in a computer, uses binary digits to represent the symbols typed on the keyboard.

Bits are binary digits that are either 1s or 0s representing as on/off switches, or the presence/absence of electrical charges, light pulses, or radio waves.

Computers are designed to use grouping of 8 bits. This grouping of 8 bits is called a byte.

Most computer coding scheme uses 8 bits to represent each number, letter, or symbol.

A series of 8 bits is called a byte. 1 byte represents a single addressable storage location.

1 bit = 1/8 bytes1 byte = 1 byte1 Kilobyte = 1000 bytes1 Megabyte = 1 million bytes1 Gigabyte = 1 billion bytes1 Terabyte = 1 trillion bytes1 Kbps = 1000 bps1 Mbps = 1 million bits per second1 Gbps = 1 billion bits per second1 Tbps = 1 trillion bits per second

Hertz [Hz] is a unit of frequency. Rate of change in the state or the cycle in a sound wave, alternating current, or other cyclical wave form. Represents one cycle per second.

Computers recognize and process data using the binary, or Base2, number system.

The Base16, or hexadecimal [hex], number system is used frequently when working with computers because it can represent binary numbers in a more readable form.

The hexadecimal number systems uses 16 symbols. Combination of these symbols represent all possible numbers.

Layer 2 Media Access Control [MAC] addresses are typically written in hex.

For Ethernet and Token Ring, these addresses are 48 bits, or six octets.

Since addresses consists of six distinct octets, they can be expressed as 12 hex numbers instead.Every 4 bits is a hex digit.

To make handling hex versions of MAC addresses even easier, the dots are placed are only placed after every four hex digits.

Most common way for computers and software to express hexadecimal output is by using 0x in front of the hexadecimal number.

To convert from hexadecimal to binary, convert every hex digit into 4 bits.

When written, the complete decimal number is represented as four groups of decimal digits separated by periods called the Dotted Decimal Notation.

Dotted Decimal Notation provides a compact, easy to remember way of referring to 32 bit addresses.

Boolean logic is based on digital circuitry that accepts one or two incoming voltages and, based on these input voltages, generate an output voltage.

Boolean logic is a binary logic that allows two numbers to compared, and then a choice based on two numbers is generated. Choices are the logical AND, OR, and NOT.

With the exception of NOT, Boolean operations have the same functions.

The 32 bit binary addresses used on the Internet are called Internet Protocol [IP] addresses.

For the computer to know how the 32 bit IP address has been split, a second 32 bit number is called a subnetwork mask is used.

The mask is a guide that indicates how the IP address should be interpreted by identifying how many of the bits identify the computer network.

Data networks developed as a result of businesses and government agencies needing to exchange electronic information across long distances.

Businesses needed a solution that would address the following concerns:1) Avoid duplication of equipment and resources2) Efficient communication3) Setup and manage a network

The solution was networking technology increase productivity while saving money.

One early solution was the creation of Local Area Network [LAN] standards.

The need for information to move efficiently and quickly not only within a company, but from one business to another, the solution to this problem was Metropolitan Area Network [MAN] and Wide Area Network [WAN].

Since WANs could connect user networks over large geographical areas, it made it possible for businesses to communicate with each other across great distances.The history of computer networking is complex, involving many people from all over the world over

the past 35 years.

The DoD's WAN eventually became the Internet.

Protocol suites are collections of protocols that enable network communication from one host through the network to another host.

A protocol is a formal description of a set of rules and conventions that govern a particular aspect of how devices on a network communicate.

Protocols determine the format, timing, sequencing, and error control in data communications.

Protocols control all aspects of data communications.

LANs consist of computers, network interface cards, peripheral devices, networking media, and network devices.

LANs make it possible for businesses that use computer technology to locally share files, and printers efficiently, and make internal communications possible.

LANs tie together data, local communications, and computing equipments.

LANs are designed to do the following:1) Operate within a limited geographical area.2) Allow many users to access high bandwidth media.3) Provide full time connectivity to local services.4) Connect physically adjacent devices.

Some common LAN technologies are:1) Ethernet2) Token Ring3) FDDI

WANs interconnect LANs, which ten provide access to computers or file servers in other locations.

WANs connect user networks over a large geographical area, it makes it possible for businesses to communicate across great distances.

WANs are designed to do the following:1) Operate over large geographically separated area.2) Allow users to engage in real time communication with other users.3) Provide full time remote resources connected to local services.4) Provide e-mail, World Wide Web, File Transfer, and E-commerce services.

Here are some common WAN technologies:

1) Modems2) Integrated Services Digital Networks [ISDN]3) Digital Subscriber Line [DSL]4) Frame Relay5) T [U.S.A] and E [Europe] carrier series – T1, E1, T3, E3, and so on.6) Synchronous Optical Network [SONET] – Synchronous Transport Signal Level 1 [STS-1]

[Optical Carrier [OC] – 1], STS – 3 [OC – 3], and so on.

A MAN is a network that spans a metropolitan area, such as a city or a suburban area.

MANs are networks that connect LANs separated by distance, and that are located within a common geographic area.

The following features differentiate MANs from LANs and WANs:1) MANs interconnect users in a geographic area or region larger that that covered by a LAN, but

smaller than the area covered by a WAN.2) MANs connect networks in a city into a single larger network. [Which can then also offer

efficient connection to a WAN]3) MANs also are used to interconnect several LANs by bridging them with backbone lines.

A Storage Area Network [SAN] is a dedicated, high performance network that moves data between servers and storage resources.

SAN technology allows high speed server to storage, storage to storage, or server to server connectivity.

SAN offers the following features:1) Performance2) Availability3) Scalability

A Data Center is a globally coordinated network of devices designed to accelerate the delivery of information over the Internet infrastructure.

A Data Center bypasses potential sources of congestion by distributing the load across a collection of content engines that are located close to the viewing audience.

One common configuration of a LAN is an intranet.

Intranet web servers differ from public web servers in that the public does not have access to an organization's intranet without proper permission and passwords.

An Extranet is an intranet that is partially accessible to authorized outsiders.

A Virtual Private Network [VPN] is a private network that is constructed within a public network infrastructure such as the global Internet.

A VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure

such as the Internet.

VPNs maintain the same security and management policies as a private network.

VPNs are most cost effective method of establishing a point to point [PPP] connection between remote users and an enterprise customer's network.

Three main types of VPNs exist:1) Access VPNs – Provide remote access for a mobile worker and Small Office/Home Office

[SOHO] to the headquarters intranet or extranet over a shared infrastructure.2) Intranet VPNs – Link regional and remote offices to the headquarters internal network over a

shared infrastructure using dedicated connections.3) Extranet VPNs – Link business partners to the headquarters network over a shared

infrastructure using dedicated connections.

VPNs have the following advantages:1) A single VPN technology can provide privacy for multiple TCP/IP applications.2) Encrypted services can be provided for all TCP/IP communications between the trusted client

and the VPN server.3) VPN provides mobility to employees and allows employees to access the corporate network

securely.

LANs and WANs have always had one thing in common: the use of the term Bandwidth to describe their capabilities.

Bandwidth is defined as the amount of information that can flow through a network connection in a given period of time.

Bandwidth is finite.

Bandwidth is not free.

Bandwidth is the key factor in analyzing network performance, designing new networks, and understanding the Internet.

The demand for Bandwidth is ever increasing.

In digital systems, the basic unit of bandwidth is bits per second [bps].

Bandwidth is the measure of how much information, or bits, can flow from one place to another in a given amount of time, or seconds.

Bandwidth varies depending on the type of medium as well as the LAN and WAN technologies used.

Bandwidth is the measure of the amount of information that can move through the network in a given period of time.

Throughput refers to actual measured bandwidth at a specific time of day, using specific Internet

routes, and while a specific set of data is transmitted on the network.

The following are some of the factors that determine throughput:1) Internetworking devices2) Types of data being transferred3) Network Topology4) Number of users on the network5) Users computer6) Server computer7) Power conditions8) Congestion

A network's theoretical bandwidth is an important consideration in network design, because network bandwidth is never greater than the limits imposed by the chosen medium and networking technologies.

Network designers and administrators are often called on to make decisions regarding bandwidth.

The OSI reference model, released in 1984, was the descriptive scheme that the ISO created.

The OSI model reference has seven numbered layers, each of which illustrates a particular network function.

Layer 7 = Application Layer [Data PDU] Layer 6 = Presentation Layer [Data PDU] Layer 5 = Session Layer [Data PDU] Layer 4 = Transport Layer [Segment PDU] Layer 3 = Network Layer [Packet PDU] Layer 2 = Data Link Layer [Frame PDU] Layer 1 = Physical Layer [Bit PDU]

This separation of networking functions is called layering. Diving the network into seven layers provides the following advantages:

1) It breaks network communication into smaller simpler parts.2) It standardizes network components to allow multiple vendor development and support.3) It allows different types of network hardware and software to communicate.4) It prevents changes in one layer from affecting the other layers so that they can be developed

more quickly.5) It breaks network communication into smaller components to make learning easier.

The application layer is the OSI layer that is closet to the user and provides networking services to the user's applications.

The presentation ensures that the information that the application layer of one system sends out can be read by the application layer of another system.

The session layer establishes, manages, and terminates sessions between two communicating hosts.

The transport layer segments data from the sending host's system and reassembles it into a data stream on the receiving host's system.

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.

The data link layer provides reliable transit of data across a physical link.

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

Peer to Peer communications is each layer of the OSI model at the source must communicate with its peer layer at the destination.

During the process of peer to peer communications, the protocols at each layer exchange information called protocol data units [PDUs], between peer layers.

The historical and technical open standard of the Internet is Transmission Control Protocol/Internet Protocol [TCP/IP].

The TCP/IP model has four layers: Layer 4 = Application Layer Layer 3 = Transport Layer Layer 2 = Internet Layer Layer 1 = Network Access Layer

Encapsulation wraps data with the necessary protocol before network transit.

Networks must perform the following five conversion steps to encapsulate data:1) Build the data2) Package the data for end to end transport3) Append [Add] the network address to the header4) Append [Add] the local address to the data link header5) Convert to bits for transmission

De-encapsulation is a process where each subsequent layer performs strips the data to be read.

Equipment that connects directly to a network segment is called a device. Broken into two classifications:

1) End User devices [Hosts]2) Network devices

Repeaters are networking devices existing at Layer 1, the physical layer, of the OSI reference model acting on the bit level, and look at no other information.

Hub is a device that has a purpose to regenerate and retime network signals. Connect segments of a LAN.

Most important properties of hubs:1) Hubs amplify signals.2) Hubs propagate signals through the network.3) Hubs do not require filtering.4) Hubs do not require path determination or switching.5) Hubs are used as network concentration points.

The area within the network where the data packets originate and collide is called a collision domain.

Network interface cards [NICs] are considered Layer 2 devices because each NIC throughout the world carries a unique code, called a Media Access Control [MAC] address. This address controls data communication for the host on the LAN.

A bridge is a Layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain. Designed to create more usable bandwidth.

Purpose of a bridge is to filter traffic on a LAN to keep local traffic local yet allow connectivity to other parts [segments] of the LAN for traffic that is directed there.

The following are the important properties of bridges:1) Bridges are more intelligent than hubs. That is, they can analyze incoming frames and forward

[or drop] them based on addressing information.2) Bridges collect and pass packets between two or more LAN segments.3) Bridges create more collision domains, allowing more than one device to transmit

simultaneously without causing a collision.4) Bridges maintain MAC address tables.

Flooding is the bridge that broadcasts the data to all devices on a network except the one on which it was received, if the destination MAC address is unknown to the bridge.

Broadcast is a data packet that is sent to all nodes on a network.

A Broadcast domain consists of all the devices connected to a network that receive data packet broadcast by a node to all other nodes on the same network.

A switch is used for multiple bridge connections.

Layer 2 switches, also called LAN switches or workgroup switches, often replace shared hubs and work with existing cable infrastructure to ensure that the switches are installed with minimal disruption of existing networks.

Like bridges, switches connect LAN segments, use a table of MAC addresses to determine the segment on which a frame needs to be transmitted and reduce traffic.

Switches operate at much higher speeds than bridges.

Switches are data link layer devices, like bridges, let multiple physical LAN segments to be interconnected into single large networks.

Similar to bridges, switches forward and flood traffic based on MAC addresses.

Microsegmentation allows the creation of private or dedicated segments – one host per segment.

A router is a type of internetworking device that passes data packets between networks based on Layer 3 addresses.

A router can make decisions regarding the best path for delivery of data on the network.

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.

Routers let virtually any type of computer communicate with any other computer anywhere in the world.

Voice gateways for handling converged packetized voice and data traffic. DSLAMs used at the service provider's central office for concentrating DSL modem

connections from hundred of homes. Cable Modem Termination System [CMTS] used at a cable operator's headend or central

location to concentrate connections from many cable modem subscribers. Optical platforms for sending and receiving data over fiber-optic cable, providing high speed

connection.

A gateway is a special purpose device that converts information from one protocol stack to another.

A digital subscribers line access multiplexer [DSLAM] is a device used in a variety of DSL technologies.

Cable operators use a Cable Modem Termination System [CMTS] at various concentration points or hubs in the cable network to provide high speed Internet access, voice, and other networking services to homes and business subscribers.

CMTS is designed for MTUs [multitenant units] such as apartment buildings, and hotels.

Several optical platforms are available for optical networking, which is primarily a backbone, wide area technology.

The term firewall refers to either a firewall program running on a router or server or special standalone hardware component of a network.

A firewall protects a private network resources from users in other networks.

A firewall examines each network packet to determine whether to forward it to its destination. An AAA server is a server program that handles user requests for access to computer and network resources.

An AAA server provides authentication, authorization, and accounting services for an enterprise.

A VPN concentrator offers powerful remote access and site to site VPN capabilities, an easy to use management interface, and a VPN client.

A wireless LAN [WLAN] provides all the features and benefits of traditional LAN technologies such as Ethernet, without the limitations of wires or cables.

Each wireless client requires a wireless NIC or client adapter. These are available as PCMCIA and PCI cards to provide wireless connectivity for both laptop and desktop workstations.

The access point [AP] or base station is a wireless LAN transceiver that can act as a hub – the center point of a standalone wireless network – or as a bridge – the connection point between wireless and wired networks.

Multiple AP s can provide roaming functionality, allowing wireless users freedom to roam throughout a facility, while maintaining uninterrupted connectivity to the network.

A wireless bridge provides high speed [11 Mbps], long range [25 miles], line of sight wireless connectivity between Ethernet networks.

Cisco AP can be used as a repeater [extension point] for the wireless network.

A network topology defines how computers, printers, network devices, and other devices are connected.

Networks can have both a physical and a logical topology.

Physical topology refers to the physical layout of the devices and media.Examples of physical topologies that are used are:

Bus Ring Star Extended Star Hierarchical Mesh

Logical topology defines how the medium is accessed by the hosts for sending data.

Commonly called a linear bus, a bus topology connects all the devices using a single cable.

The Star topology is the most commonly used physical topology in Ethernet LANs.

The logical ring topology is another important topology in LAN connectivity. Hosts are connected in the form of a ring or circle.Two types of rings exist:

1) Single Ring2) Dual Ring

Single Ring shows all the devices on the network share a single cable, and the data travels in one

direction only. Actually wired as a star.

In dual ring, two rings allow data to be sent in both directions. This setup creates redundancy [fault tolerance], meaning that if one ring fails, data can be transmitted on the other ring. Also, if both rings fail, a “wrap” at the fault can heal the topology back into a ring.

A hierarchical topology is created similar to an extended star topology. Only difference is that it does not use a central node, instead it uses a trunk mode where it branches to other nodes.

Two types of tree topologies exists:1) Binary Tree [Each node split into two links]2) Backbone Tree [A backbone trunk has branch nodes with links hanging from it]

The full mesh topology connects all devices [nodes] to each other for redundancy and fault tolerance.

In a partial mesh topology, at least one device maintains multiple connections to others without being fully meshed.

A network's topology is how the hosts communicate across the medium.

Two most common type of logical topology are broadcast and token passing.

Broadcast topology simply means that each host addresses its data to a particular NIC, to a multicast address, or to a broadcast address on the network medium.

Token passing controls network access by passing an electronic token sequentially to each host.

The function of the physical layer is to transmit data by defining the electrical, wireless, or light specifications between the source and destination.

The basic unit of all matter in the universe is the atom.

The atom is made of three tiny parts: protons, neutrons, and electrons.

The protons and neutrons are lumped together in a small grouping called a nucleus.

The electrons flows freely around this nucleus.

Protons – Particles that have a positive charge.Neutrons – Particles that have no charges.Electrons – Particles that have a negative charge.

When the three pars come together, they form an atom.

The Periodic Table of Elements list all known types of atoms and their properties.

Atoms normally have equal number of protons and electrons and since equal, it does not have no net charge.

Atoms bond together in different combinations to form molecules of various matter.

The nucleus of an atom is bound together by a very powerful force.

Insulators are materials made of atoms or molecules that require a great deal of force to remove their electrons from orbit. Electrons flow poorly. [Plastic, Paper, Rubber, Pure water, Glass, air, and dry wood]

Conductors are materials made of atoms or molecules with electrons that are bound loosely to the nucleus and require little force to remove them from orbit. Electrons flow well. [Copper [Cu]]

Semiconductors are materials made of atoms or molecules with electrons whose movement can be precisely controlled. Electrons flow can be controlled precisely. [Silicon [Si]]

Voltage is the force that when the charges are separated, this separation creates an attractive force or pressure field between the charges.

The force that is created pulls toward the opposite charge and pushes away from the like charge.

Voltage is represented by the letter V. The unit of measurement for voltage is volt.

Two kinds of voltage exists:1) Direct Current [D.C.] voltage – The movement of electrons in a DC circuit is always in the

same direction, from negative to positive.2) Alternating Current [A.C.] voltage – In an AC current, the positive and negative terminals of the

AC voltage source regularly change to negative and positive and back again. This change makes the direction of electron movement change, or alternate, with respect to time.

Electrical current is the flow of charges that is created when electrons move.

Current is represented by the letter I and the unit of measurement for current is ampere.

Current that results from DC voltage always flows in the same direction from negative to positive.

Current that results from AC voltage flows in one direction, then changes direction, and then alternates back to the original direction, and so on.

Wattage is electrical power calculated from amps multiplied to voltage.

Resistance is the property of a material that resists electron movement.

Conductors have low resistance, and insulators have high resistance.

The term resistance is generally used when referring to DC circuits.

The resistance to the movement of electrons in an AC circuit is called Impedance and its unit of measurement is ohms.

Electrons move best through conductive materials.

Copper is the most common medium for signal wiring.

Copper has several important properties that make it well suited for electronic cabling:1) Conductivity2) Corrosion resistance3) Ductility4) Malleability5) Strength

Two types of copper cable used for networks:1) Twisted Pair – Twisted pair cables are composed of one or more pairs of copper wires. Most

data and voice networks use twisted pair cabling.2) Coaxial – Coaxial cable has one center conductor of either solid or stranded copper wire. Once

the choice for Local Area Network [LAN] cabling, but it is now primary used for video connections, high speed connections such as T3 [or E3] lines, and cable televisions.

The diameter of cable wires or conductors is commonly measured using the American Wire Gauge [AWG] system.

AWG is a U.S. Standard for measuring the diameter of primary copper and aluminium cable.

Twisted pair cable is a type of cabling that is used for telephone communications and most modern Ethernet networks.

A pair of wires forms a circuit that can transmit data. Provides protection against crosstalk, the noise generated by adjacent pairs.

Shielded twisted pair [STP] cable contains four pairs of thin, copper wires covered in colour coded plastic insulation that are twisted together.

Noise reduction provides a major advantage of STP over unshielded cable. The not so great thing is that it is more difficult to install due to the metallic shielding needing to be grounded.

Summarizations of STP cable features:1) Speed and Throughput – 10 to 100 Mbps2) Average cost per node – Moderately Expensive3) Media and Connector size – Medium to Large4) Maximum cable length – 1000 meters [m] [short]

Unshielded Twisted Pair Cable is a common networking media consisting of four pairs of thin, copper wires covered in colour coded plastic, insulation that are twisted together.

The connector used on a UTP cable is called a registered jack 45 [RJ-45] connector.

UTP cable has many advantages: Small diameter and no requirement for grounding. Easy to install.

Fit in a given area than other copper media. Least expensive type of networking media. Connector easiest to build. Supports same data speeds as other copper media.

UTP disadvantage is that it is more susceptible to electrical noise and interference than any other type of networking media.

UTP another disadvantage is that its maximum run length is less than that allowed for coaxial and fiber-optic cables.

Summarizations of UTP cable:1) Speed and Throughput – 10 to 1000 Mbps2) Average cost per node – Least Expensive3) Media and Connector size – Small 4) Maximum cable length – 100m [short]

Commonly used types of UTP cabling are as follows:1) Category 1 [CAT1] – Used for telephone communications. Not suitable for transmitting data.2) Category 2 [CAT2] – Capable of transmitting data at speeds up to 4 Mbps.3) Category 3 [CAT3] – Used in 10BASET Ethernet networks. Can transmit data at speeds up to

10 Mbps.4) Category 4 [CAT4] – Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps.5) Category 5 [CAT5] – Can transmit data at speeds up to 100 Mbps. Used in Fast Ethernet

networks.6) Category 5 [CAT5e] – Used in networks running at speeds up to 1000 Mbps [1 Gbps]. Used in

Gigabit Ethernet [GigE] networks.7) Category 6 [CAT6] – The specification for CAT6 is new, was released on February 3rd , 2003,

and is currently available for installation and use. Used in Gigabit Ethernet [GigE] networks.

Comparing UTP and STP notes:1) The speed of both types of cable is usually satisfactory for local area distances.2) These are the least expensive media for data communication. UTP is less expensive than STP.3) Because most buildings are already wired with UTP, many transmissions standards are adapted

to use it to avoid costly rewiring with an alternate cable type. Must take care to ensure that the category level of the cable is adequate to handle the bandwidth desired.

Coaxial cable consists of four main parts:1) Copper conductor2) Plastic insulation3) Braided copper shielding4) Outer jacket

Coaxial cable was a popular choice with LANs in the past.

Coaxial cable offered several advantages: Run with fewer boosts from repeaters for longer distances between network nodes than either

STP or UTP cable. Less expensive than fiber-optic cable despite being expensive than UTP.

Technology is well known because it has been used for many years in various types of data communications.

The largest diameter [1 cm] was once specified for use as Ethernet backbone cable because it had greater transmission length and better noise rejection characteristics than other types of cable. This type of coaxial cable is frequently referred to as Thicknet [rigid cable].

Coaxial cable with a diameter of 0.35 cm, sometimes referred to as Thinnet, was also frequently used in Ethernet networks at one time. Useful for cable installations that required the cable to make many twists and turns. Easier and cheaper to install, thus referred to as Cheapernet.

Summarizations features of Coaxial cable:1) Speed and Throughput – 10 to 100 Mbps2) Average cost per node – Inexpensive3) Media and Connector size – Medium4) Maximum cable length – 500m [medium]

Specifications, or Standards, are sets of rules or procedures that are widely used and serve as the accepted method of performing a task.

The Institute of Electrical and Electronic Engineers [IEEE] has outlined LAN cabling specifications.

IEEE802.3 is a standard for Ethernet networks and IEEE802.5 is a Token Ring standard.

The Underwriters Laboratories issues standards that are primarily concerned with safety.

The Telecommunications Industry Association [TIA] and the Electronic Industry Association [EIA] have jointly issued cabling standards often called TIA/EIA standards:

TIA/EIA 568B = This is a commercial building telecommunication cabling standard. TIA/EIA 569B = Formally the TIA/EIA 568A standard. This is a commercial building standard

for telecommunication pathways and spaces. TIA/EIA 570A = This is a residential and light commercial telecommunication wiring standard. TIA/EIA 606 = This is an administration standard for the telecommunications infrastructure of

commercial buildings. TIA/EIA 607 = This is a commercial building groundings and bonding requirement for

telecommunication.

TIA/EIA 568B calls for two cables to each work area outlet:1) A telephone cable for voice.2) A network cable for data.

The voice cable must be a 2 pair UTP cable with its correct connectors, or terminators. The network cable must be one of the following and must include the correct connectors or terminators:

150 ohm STP 2 pair cable [Token Ring LANs] 100 ohm UTP 4 pair cable [Ethernet LANs] 62.5/125 µ fiber-optic cable [Ethernet LANs] Coaxial Cable [Not needed since it is already obsolete]

Optical fiber is most frequently used medium for the longer, high bandwidth, point to point transmissions required on LAN backbones, and on wide area networks [WANs].

Good reasons for Optical Fiber used in networks because:1) Fiber is not Susceptible to Lightning, Electromagnetic Interference [EMI], or Radio Frequency

Interference [RFI], and it does EMI or RFI.2) Fiber has much greater bandwidth capabilities than other media.3) Fiber allows significantly greater transmission distances and excellent signal quality because

very little signal attenuation occurs.4) Fiber is more secure than other media because it is difficult to tap into a fiber and easy to detect

someone's placing a tap on the fiber.5) Current Fiber transmitter and receiver technologies can be replaced by newer, faster devices as

they are developed so that greater transmission speeds can be achieved over existing Fiber links with no need to replace the fiber.

6) Fiber cost less than copper for long distance applications.7) The raw material that fiber is made from is sand, a plentiful substance.8) With Fiber, you have no grounding concerns as you have when signaling using electricity.9) Fiber is light in weight and easily installed.10) Fiber has better resistance to environmental factors, like water, than copper wire.11) Lengths of Fibers can easily be spliced together for very long cable runs.

Fiber optics is used when a large number of bits need to sent over distances greater than 100 meters.

An important property of any energy wave is its wavelength.

The wavelength of an electromagnetic wave is determined by how frequently the electric charge that generates the wave moves back and forth.

Electromagnetic waves generated in same way, all these waves share many of the same properties.

Human eyes can sense electromagnetic energy only with wavelengths between 700 nanometres and about 400 nanometres.

A nanometre is one billionth of a meter in length and is abbreviated nm.

Electromagnetic energy with wave lengths between 700nm and 400nm is called visible light.

To transmit data over optical fiber, wavelengths that are not visible to the human eye are used are called Infra Red that its wavelength is slightly longer than red light.

The wavelength of the light in optical fiber is one of the following wavelengths:1) 850 nm2) 1310 nm3) 1550 nm

Selected wavelengths travel better through optical fiber than other wavelengths.

When electromagnetic waves, including lights, travel out from the source, they travel in straight lines

are called rays.

Refracted Rays is the light energy in the incidental ray that is not reflected enters the glass bent at an angle from its original path.

Two factors determine incidental ray being bent:1) The angle at which the incidental ray strikes the surface of the glass.2) The different rates of speed at which light travels through the two substances. [air and glass]

The bending of light rays at the boundaries of two substances is the reason why light rays are able to travel through an optical fiber even if the fiber curves in a circle.

The laws of reflection and refraction tells how to design a fiber that guides the light waves through the fiber with a minimum energy loss.

Two conditions are needed to cause light rays in a fiber to be reflected back into the fiber with out any loss to refraction are:

1) The core [the inside] of the optical fiber has to have a larger [a higher] index of refraction than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding.

2) The angle of incidence of the light ray is greater than the critical angle for the core and its cladding.

Total Internal Reflection is all the incident light in the fiber reflected back inside the fiber, when the above two conditions are met.

Fiber optic cable is a networking medium that uses modulated lights for data transmission through thin strands of glass.

Signals that represent data bits are converted into beams of light.

Five parts typically make up each fiber optic cable:1) The core2) The cladding3) A buffer4) A strengthening material 5) An outer jacket

Multimode fiber allows multiple modes [paths] of light to propagate through the fiber optic core.

Single mode fiber allows only one mode of light to propagate through the fiber optic core. The following summarizes the features of fiber optic cables:

1) Speed and Throughput – More than 1Gbps2) Average cost per node – Expensive 3) Media and connector size – Small4) Maximum cable length – More than 10 kilometres [km] for single mode; up to 2 km for

multimode.

Two basic cable designs exists:

1) Loose-tube2) Tight-buffered

Transmitters receive data to be transmitted from switches and routers.

Two sources of transmitters are:1) Light Emitting Diodes [LEDs]2) Light amplification by stimulated emission radiation [Laser]

Each light source can be lighted and darkened quickly to send data 1s and 0s at a high number of bits per second.

Wireless signals are electromagnetic waves that can travel through the vacuum of outer space or through a medium such as air.

Wireless is a versatile way to build a network.

The radio spectrum is part of the electromagnetic spectrum used to transmit voice, video, and data.

Each type of wireless data communications has it advantages and drawbacks, as follows: Infrared [IR]: Very high data rates and lower cost, but very short distance. Narrowband: Low data rates and medium cost. Requires a licence and covers a limited distance. Spread Spectrum: Medium cost and high data rates. Limited to campus coverage, Cisco Aironet

products are spread spectrum. Broadband Personal Communications Service [PCS]: Low data rates, medium cost, and city

wide coverage. With the exception of Sprint, they provide nationwide and international coverage.

Circuit and Packet Data [Cellular Data and Cellular Digital Packet Data [CPDPD]]: Low data rates, high packet fees, and national coverage.

Satellite: Low data rates, high cost, and nationwide or worldwide coverage.

Three factors for RF efficiency:1) Type of modulation used2) Distance3) Noise

A wave is energy travelling from one place to another.

The frequency is the number of waves that reach the shore each second.

The amplitude of an electrical signal represents its height measured in volts, instead of meters.

The frequency of an electrical signal is the number of complete cycles [or waves] per second and is measured in hertz.

If a disturbance is deliberately caused and involves a fixed predictable duration, it is called a pulse.

An important way of describing networking signals is a unit of measure called the decibel [db].

Analog bandwidth typically refers to the frequency range of an analog electronic system.

Digital bandwidth measures how much information can flow from one place to another in a given amount of time. Bits per second.

A straight through cable that maintains the pin connection all the way through the cable.

A crossover cable crosses the critical pair to properly align, transmit, and receive signals on the device with line connections.

Ethernet in its various forms is the most widely used Local Area Network [LAN] technology.

Data Link Layer has two sublayers:1) Media Access Control2) Logical Link Control

A broadcast domain is a grouping of collision domains that are connected by Layer 2 devices.

A bridge is a Layer 2 device designed to create two or more LAN segment, each of which is a separated collision domain in order to create more usable bandwidth.

Latency, sometimes called propagation delay is that time that a frame, or packet, of data takes to travel from source station to node to its final destination on the network.

Store and Forward switching, the switch reads the entire frame of data, checks the frame for errors, decides where it needs to go, and then sends it on its way.

Cut through switching, the switch reads the beginning of the frame up to the destination MAC address as the traffic flows through the switch and cuts through to its destination without continuing to read the rest of the frame. No error detection.

Fragment free switching is a modified form of cut through switching. Filters out collision fragments, which are the majority of packet errors before forwarding begins.

Synchronous switching is where both the source and destination ports must operating at the same bit rate to keep the frame intact.

Asynchronous switching is where if the bit rates are not the same, the frame must be stored at one bit rate before it is sent out at the other bit rate.Switches have five STP operating modes:

1) Blocking2) Listening3) Learning4) Forwarding5) Disabled

TCP model Layer 4 = Application

Layer 3 = Transport Layer 2 = Internet Layer 1 = Network Access

IP Addressing

Class A = 1.0.0.0 – 126.0.0.0 [127.0.0.1 is a loopback address] /8Class B = 128.0.0.0 – 191.162.0.0 /16Class C = 192.168.0.0 – 223.0.0.0 /24Class D = Multicast AddressClass E = Experimental

Essential two methods of assigning IP addresses:1) Static Addressing2) Dynamic Addressing

A protocol is standards based set of rules that determines how computers communicate with each other across networks.

Routed protocol – Any network protocol that provides enough information in its network layer address that allows a packet to be forwarded from one host to another host based on the addressing scheme. Defines the field formats within a packet.

Routing protocols – Supports 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.

Both the IP address and network mask [subnet mask] are required to have a routed network.

An Autonomous System is a network or set of networks that are under the administrative control of a single entity.

The distance vector routing approach determines the direction [vector] and distance [hop count] to any link in the internetwork.

The link state routing protocols were designed to overcome the limitations of distance vector routing protocols.

The term connectionless means no dedicated circuit connection is required, as there would be for a telephone call.

At the network layer, the data is encapsulated within packets called datagrams.

In connection oriented systems, a connection is established between the sender and the recipient before any data is transferred.

Anatomy of an IP packet:1) Version

2) IP Header Length [HLEN]3) Type of Service [TOS]4) Total Length5) Identification6) Flags7) Fragment Offset8) Time to Live [TTL]9) Protocol10) Header checksum11) Source IP address12) Destination IP address13) Options14) Padding15) Data

A Wide Area Network [WAN] is a data communication network that extends across a large geographical area.

A router initializes by loading the bootstrap, the operating system, and a configuration file.

The router stores configuration files created from setup mode or created manually without setup mode in the Non Volatile Random Access Memory [NVRAM].

When a Cisco router or switch powers up, it performs a power on self test [POST] to check whether everything is in check or not.

Two EXEC mode in the Cisco IOS exists:1) User mode2) Privilege Mode [or enable mode]

Cisco Discovery Protocol [CDP] is a Layer 2 protocol that connects lower physical media and upper network layer protocols. Used to obtain information about neighbouring devices.

Includes the following in show cdp neighbours command:1) Device ID2) Local Interface3) Holdtime4) Capability5) Platform6) Port ID7) VTP Management Domain Name [CDPv2 only]8) Native VLAN [CDPv2 only]9) Full/Half Duplex [CDPv2 only]

Telnet is a virtual terminal protocol that is part of the TCP/IP protocol suite.

Telnet enables you to make connections to remote hosts and mask it possible for a network terminal to remotely log in.

Telnet performs at the application layer of the OSI model, and it depends on TCP to guarantee the correct and orderly delivery of data between the client and server.

A router can have simultaneously incoming Telnet sessions.

Five incoming Telnet sessions can take place at one time.

Path determination for traffic going through a network cloud occurs at the network layer [Layer 3].

A router generally relays a packet from one data link to another using two basic functions:1) A path determination function2) A switching function

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. Define field formats within a packet. Conveyed from end system to end system. Uses routing table to forward packets.

Routing Protocol – Supports a routed protocol by providing mechanisms for sharing routing information. Messages move between the routers. Allows the routers to communicate with other routers to update and maintain tables.

Route Source Default Distance Values

Connected Interface 0Static Route 1EIGRP [Summary Route] 5External BGP 20Internal EIGRP 90IGRP 100OSPF 110IS-IS 115RIP 120EGP 140External EIGRP 170Internal BGP 200Unknown 255

The metric characteristics that most commonly used by routers are as follows:1) Bandwidth2) Delay3) Load4) Reliability5) Hop Count6) Ticks7) Cost

Most routing algorithms can be classified under one of the following three categories:

1) Distance Vector – Determines the direction, or the vector and the distance to any link in the internetwork.

2) Link State – Also called Shortest Path First, recreates the exact topology of the entire internetwork.

3) Balanced Hybrid – Combines the aspects of the link state and distance vector algorithms.

Link State routing uses the following:1) Link State Advertisements – Small packets of routing information that are sent between routers.2) Topological Database – A collection of information gathered from LSA's.3) Shortest Path First [SPF] algorithm – A calculation performed on the database resulting in the

SPF tree.4) Routing Table – A list of the known paths and interfaces.

Running link state protocols brings up three primary concerns:1) Processor overhead2) Memory requirements3) Bandwidth consumption

An Interior Gateway Protocol [IGP] is designed for use in a network controlled or administered by a single organization. Designed to find the best path through the network.

An Exterior Gateway Protocol [EGP] is designed for use between networks that are controlled by two different organizations. Typically are used between the Internet Service Providers [ISPs] or between a company and an ISP. Must isolate Autonomous Systems.

EGPs require the following three sets of information before routing can begin:1) A list of neighbour routers to exchange routing information with.2) A list of networks to advertise as directly reachable.3) The Autonomous System number of the local router.

To reduce routing loops and counting to infinity, use the following methods:1) Split horizon2) Poison reverse3) Hold down timers4) Triggered updates

ICMP is the component of the TCP/IP protocol stack that addresses IP's failures to ensure data delivery.No overcome unreliability limitations that exists in IP.ICMP messages are delivered using the IP protocol encapsulated into datagrams.

ICMP messages formats start with the following three fields:1) Type2) Code3) Checksum

ICMP Message Type 0 Echo Reply3 Destination unreachable

4 Source quench5 Redirect/Change request8 Echo request9 Router advertisement10 Router selection11 Time exceeded12 Parameter problem13 Timestamp required14 Timestamp reply15 Information request16 Information reply17 Address mask request18 Address mask reply

Code Value Description 0 Network Unreachable1 Host Unreachable2 Protocol Unreachable3 Port Unreachable4 Fragment needed and DF set5 Source route failed6 Destination network unknown7 Destination host unknown8 Source host isolated9 Communication with data administratively prohibited10 Communication with data host administratively prohibited11 Network Unreachable for type of service12 Host unreachable for type of service

Default-gateways send ICMP redirects/change requests only if the following conditions are met:1) The interface on which the packets comes into the router is the same interface on which the

packet gets routed out.2) The subnet/network of the source IP address is the same subnet/network of the next hop IP

address of the routed packet.3) The datagram is not source routed [that is, it is not routed from the place from which the data is

taken.].4) The route for the redirect is not another ICMP redirect or a default route.

5) The router is configured to send redirects. By default, Cisco routers send ICMP redirects. The interface subcommand no ip redirects disables ICMP redirects.

Code Value Required Action 0 Redirects datagrams for the network1 Redirects datagrams for the host2 Redirects datagrams for the type of service and the network3 Redirects datagrams for the type of service and the host

ICMP Field Description

Type 17 Address mask request messageType 18 Address mask reply messageCode 0 Address mask request messageCode 0 Address mask reply messageChecksum The 16 bit 1s complement of the 1s complement sum of the ICMP

message starting with ICMP type. For computing the checksum, the checksum field should be 0. The checksum might be replaced in the future.

Identifier An identifier to aid in matching requests and replies. It can be 0.Sequence Number A sequence number to aid in matching requests and replies. It can

be zero.Address Mask A 32bit mask. A gateway receiving an address mask request

should return it with the Address Mask field set to the 32 bit mask of the bits identifying the subnet and the network for the subnet on which the request was received. If the requesting host does not know its own IP address, it can leave the source field 0; the reply should be broadcast. However this approach should be avoided if at all possible because it increases the superfluous broadcast lead on the network. Even when the replies are broadcast, there is no need to match requests with replies because there is only one possible address mask for a subnet. The Identifier and Sequence Number fields can be ignored. Type AM2 can be received from a gateway, or a host acting in lieu of a gateway.

TCP/IP is universally available protocol that you likely use at work.TCP/IP is a useful reference for understanding other protocols because it includes elements that representative of other protocols.TCP/IP is important because the router uses it as a configuration tool.

Routers provide basic traffic filtering capabilities such as blocking internet traffic, with Access Control Lists [ACLs].

An ACL is a sequential collection of permit or deny statements that apply to addresses or upper layer protocols.

Common ACL functions include the following:1) Filtering packets internally2) Protecting the internal network from illegal Internet access3) Restricting access to virtual terminal ports.

ACLs applied to routers interfaces.

ACLs can do the following:1) Limit traffic and increase network performance. Queuing ensures that routers will not process

packets that are not needed limiting network traffic and reduce network congestion.

2) Provide traffic flow control.3) Provides basic level of security for network access.4) Decides which type of traffic is forwarded or blocked at the router interface.

An ACL is a group of statements that define how packets do the following:1) Enter inbound router interface.2) Relay through the router.3) Exit outbound router interface.

Protocol Ranges IP 1 to 99Extended IP 100 to 199Apple Talk 600 to 699IPX 800 to 899Extended IPX 900 to 999IPX Service Advertising Protocol 1000 to 1999

A Wildcard Mask is a 32 bit quantity that is divided into four octets, with each octet containing 8 bits paired with an IP address.

Standard ACLs check the source address of routed IP packets and compare it against the statements defining the ACL.

Extended ACLs are used more often than standard ACLs because they provide a greater range of flexibility and control.

Name ACLs were introduced in Cisco IOS Software Release 11.2, which allowed standard and extended ACLs to be given names instead of numbers.

Benefits of Named ACLs are:1) Intuitively identifies an ACL using an alpha or alphanumeric name.2) Eliminates the limit of 99 simple and 100 extended ACLs.3) Enables administrators to modifies ACLs without having to delete and then reconfigure them.

ACLs control traffic by filtering packets and eliminating unwanted traffic on a network.

A firewall is a computer or networking device that exists between the user and the outside world to protect the internal network from intruders. Prevent unwanted and illegal access.