Basic Router Configuration

Warren ToomeyGCIT

Introduction

A Cisco router is simply a computer that receives packets and forwards them on based on what is in the routing table

– ROM to hold the boot code

– RAM for memory when operating

– Flash to hold the operating system (IOS)

– NVRAM to hold the configuration file

– CPU to do the processing

– Network interfaces to receive and send packets

Network Interfaces

Ethernet ports (FastEthernet, GigaEthernet) connect the router to the LAN

WAN ports (Serial) connect the router to other routers using a Wide Area Network

Which Cables? Straight-through Ethernet cables:

– Router to switch, PC to switch Crossover (red) Ethernet cables:

– Router to router, PC to PC, switch to switch WAN cables:

– Router to router

– One side is the DCE (clock) Rollover cables:

– PC serial to router console port

User Interface to Router

There is only a command-line interface, accessed via a serial port (like USB but slower)

Use a serial communication program like Hyperterminal or Putty

Packet Tracer has a CLI tab to simulate the CLI

The Booting Process

show version command

User, Privileged and Config Modes

User mode: view state but make no changes Privileged EXEC mode: view state, make changes Global config mode: make configuration changes The prompt changes as you go into each mode Router> enable (User mode) Router# config t (Privileged EXEC mode) Router(config)# exit (Global config mode) Router# exit (back to privileged EXEC mode) Router> (back to user mode)

Basic Configuration

This is done in global configuration mode

Configuring the Interfaces Select the interface by name, then configure it

Configuring the Interfaces One side of a router to router connection needs to be

wired as a DCE, with a clock rate set

Verifying the Router's Config/Status show running-config

Show the current running configuration of the router

show interfaces

Show the state of all the router's network interfaces

show ip route

Show the contents of the routing table

show ip interface brief

Show the network interfaces which have IP addresses

Saving the Configuration

If you don't save the configuration, it will be lost when you do a reboot

To save the configuration:

– copy running-config startup-config To see the configuration file in NVRAM:

– show startup-config To reboot the router: reload Note: the startup configuration and the running

configuration can be different!

Connected, Static and Dynamic Routes

Configuring Static Routes

Examples:

– ip route 172.16.1.1 255.255.255.0 5.6.7.8

– ip route 196.45.7.32 255.255.255.248 serial 0/0/0

Configuring a Default Route

ip route 0.0.0.0 0.0.0.0 {ip-address|exit-interface} Use this when there is only one way out to the rest of the

internet, so there is no need for dynamic routing

– Example: home router To remove static or default route, repeat the original

command with the word no at the beginning:

no ip route 172.16.1.1 255.255.255.0 5.6.7.8

Configuring RIPv1 Routing

We want to set up dynamic routing using RIPv1 for this network topology

What commands to configure the Router interfaces?

Configuring RIPv1 Routing

On each router, enable RIP routing and list the networks that we want to advertise

Verifying RIPv1 Routing How many IP subnets are in this diagram?

How many subnets are directly connected to R1? How many subnets will R1 learn using RIP?

Verifying RIPv1 Routing On router R1

120/1 means 1 hop away, 120/2 means 2 hops away “via” gives next router's IP address and exit interface

Verifying RIP v1 Routing

Verifying RIP v1 Routing debug ip rip

– turns on RIP debugging output

undebug all

– turns off all debugging output

Verifying RIP v1 Routing debug ip rip

– turns on RIP debugging output

undebug all

– turns off all debugging output

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