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
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)
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!
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 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