9 - router fundamentals

8/14/2019 9 - Router Fundamentals

1/51

Fundamentals A router is a special type of computer.

It has the same basic components as a

standard desktop PC. It has a CPU, memory, a system bus, and

various input/output interfaces.

However, routers are designed toperform some very specific functions thatare not typically performed by desktopcomputers.


2/51

Fundamentals Just as computers need operating systems to

run software applications, routers need theInternetwork Operating System software (IOS)

to run configuration files. These configuration files contain the instructions

and parameters that control the flow of traffic inand out of the routers.

Specifically, by using routing protocols, routersmake decisions regarding the best path forpackets


3/51

Components


4/51

Components RAM, has the following characteristics and

functions: Stores routing tables

Holds ARP cache Holds fast-switching cache Performs packet buffering (shared RAM) Maintains packet-hold queues Provides temporary memory for the configuration

file of the router while the router is powered on Loses content when router is powered down or

restarted


5/51

Components NVRAM has the following

characteristics and functions: Provides storage for the startup

configuration file

Retains content when router is

powered down or restarted


6/51

Components Flash memory has the following

characteristics and functions: Holds the operating system image (IOS) Allows software to be updated without removing

and replacing chips on the processor Retains content when router is powered down or

restarted Can store multiple versions of IOS software Is a type of electronically erasable, programmable

ROM (EEPROM)


7/51

Components ROM has the following characteristics

and functions:

Maintains instructions for power-on selftest (POST) diagnostics

Stores bootstrap program and basicoperating system software

Requires replacing pluggable chips on themotherboard for software upgrades


8/51

Interfaces Interfaces have the following

characteristics and functions: Connect router to network for packets

entry and exit

Can be on the motherboard or on a

separate module


9/51

InterfacesThe interfaces are the router

connections to the outside.

The three types of interfaces arelocal-area network (LANs), wide-area network (WANs), and

Console/AUX


10/51

InterfacesThe LAN interfaces are usually one

of several different varieties of

Ethernet or Token Ring.These interfaces have controller

chips that provide the logic forconnecting the system to the media.

The LAN interfaces may be a fixedconfiguration or modular.


11/51

InterfacesThe WAN interfaces include serial,

ISDN, and integrated Channel

Service Unit (CSUs). As with LAN interfaces, WAN

interfaces also have specialcontroller chips for the interfaces.

The WAN interfaces may be a fixedconfiguration or modular.


12/51

InterfacesThe Console/AUX ports are serial ports

used primarily for the initial

configuration of the router.These ports are not networking ports.

They are used for terminal sessions fromthe communication ports on thecomputer or through a modem.


13/51

Segmentation


14/51

Internetworking


15/51

Functions They operate at Layer 3 of the OSI model,

making decisions based on networkaddresses.

The two main functions of a router are theselection of best path for and the switchingof packets to the proper interface.

Routers accomplish this by building routingtables and exchanging network informationwith other routers


16/51

Functions An administrator can maintain

routing tables by configuring static

routes. But generally routing tables are

maintained dynamically through theuse of a routing protocol.

Routing protocol exchanges networktopology (path) information withother routers


17/51

Functions

A correctly configured internetworkprovides the following:

Consistent end-to-end addressing Addresses that represent network

topologies

Best path selection

Dynamic or static routing Switching


18/51

Layers

A WAN is said to operate at the physicallayer and at the data link layer.

It simply means that the characteristicsthat separate a WAN from a LAN aretypically found at the physical layer andthe data link layer.

In other words, the standards andprotocols used in WANs at Layer 1 andLayer 2 are different from those used inLANs at the same layers


19/51

DTE-DCE

The WAN physical layer describes the interfacebetween the data terminal equipment (DTE) andthe data circuit-terminating equipment (DCE).

Generally, the DCE is the service provider andthe DTE is the attached device.

In this model, the services offered to the DTE aremade available through a modem or a CSU/DSU

CSU/DSU is used to convert the data from theDTE into a form acceptable to the WAN serviceprovider


20/51

DTE-DCE


21/51

Functions

The principal function of a router is routing. Routing occurs at the network layer, Layer 3,

but if a WAN operates at Layers 1 and 2, is a

router a LAN device or a WAN device? The answer is both, as is so often the case in

the field of networking. A router may be exclusively a LAN device, it

may be exclusively a WAN device, or it may sit

at the boundary between a LAN and a WAN andbe a LAN and WAN device at the same time.


22/51

Functions

Routing is a major function of routers

Equally important is providing connections to andbetween the various WAN physical and data-link

standards

ISDN with PPP and T1 with Frame Relay

Router should be able to move data from oneinterface to another interface


23/51

Physical Layer

WAN physical layer standards and protocols: EIA/TIA-232 EIA/TIA-449

V.24 V.35 X.21 G.703 EIA-530 ISDN T1, T3, E1, and E3 xDSL SONET (OC-3, OC-12, OC-48, OC-192)


24/51

Data Link Layer

WAN data link layer standards and protocols: High-level data link control (HDLC) Frame Relay

Point-to-Point Protocol (PPP) Synchronous Data Link Control (SDLC) Serial Line Internet Protocol (SLIP) X.25 ATM LAPB ( Link Access Procedure Balanced ) LAPD ( Link Access Procedure on D Channel ) LAPF ( Link Access Procedure for Frame Relay )


25/51

Internal Components


26/51

Functions of Components


27/51

Main Board


28/51

Mother Board


29/51

1700 Front View


30/51

1700 Rear View


31/51

1700 Expansion Cards


32/51

2600 Front View


33/51

2600 Rear View


34/51

2600 Expansion Cards


35/51

Configuration Ports

The console port and the auxiliary (AUX)port are management ports.

These asynchronous serial ports are notdesigned as networking ports. One of these two ports is required for

the initial configuration of the router.

The console port is recommended forthis initial configuration.

Not all routers have an auxiliary port.


36/51

Configuration Ports

When the router is first put into service,there are no networking parametersconfigured.

Therefore the router cannot communicatewith any network. To prepare for initial startup and

configuration, attach an RS-232 ASCIIterminal, or a computer emulating an ASCII

terminal, to the system console port. Then configuration commands can be

entered to set up the router.


37/51

Configuration Ports


38/51

Configuration Ports


39/51

Configuration Ports

Once this initial configuration is enteredinto the router through the console or

auxiliary port, the router can then beconnected to the network fortroubleshooting or monitoring.

The console port is also preferred over

the auxiliary port for troubleshooting.


40/51

Configuration Ports


41/51

Configuration Ports

To connect to the console port, arollover cable and a RJ-45 to DB-9

adapter are used to connect a PC. Cisco supplies the necessary

adapter to connect to the console

port.


42/51

Configuration Ports

The PC or terminal must supportVT100 terminal emulation.

Terminal emulation software suchas HyperTerminal is usually used.


43/51

Configuration Ports

To connect the PC to a router: Configure terminal emulation software on the PC for:

The appropriate com port 9600 baud 8 data bits No parity 1 stop bit No flow control

Connect the RJ-45 connector of the rollover cable to therouter console port.

Connect the other end of the rollover cable to the RJ-45to DB-9 adapter.

Attach the female DB-9 adapter to a PC.


44/51


45/51

Connections

In most LAN environments, the router isconnected to the LAN using an Ethernetor Fast Ethernet interface.

The router is a host that communicateswith the LAN via a hub or a switch.

A straight-through cable is used tomake this connection.

A 10/100BaseTX router interfacerequires Category 5 or better,unshielded twisted-pair (UTP) regardlessof the router type.


46/51

Connections

In some cases the Ethernetconnection of the router is

connected directly to the computeror to another router.

For this type of connection, a

crossover cable is required.


47/51

Connections

Straight through Switch to Router

Cross-over Router to Router

Router to PC

Roll-over Console port to console


48/51

Connections

The most commonly used routerinterfaces for WAN services are

serial interfaces What is the type of connection to

the Cisco device?

Is the network system beingconnected to a DTE or DCE device?


49/51

Connections

What signaling standard does thedevice require?

Is a male or female connectorrequired on the cable?


50/51

Connections


51/51

Connections

9 - router fundamentals

Documents