Basic Router Configuration Warren Toomey GCIT

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 – ip route serial 0/0/0

Configuring a Default Route ip route {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

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

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

Troubleshooting Tools