Setting and changing routes is a common enough requirement on a network.

Cisco Commands useful for managing routes include:

  • show ip route
  • no ip route IP NETMASK GATEWAY
  • ip route IP NETMASK GATEWAY

All commands are functional only inside the 'terminal' configuration prompt "...(config)#"

show ip route

Let's you see the routing configuration. Related commands include:

For example:

#show ip route
Default gateway is not set
Host Gateway Last Use Total Uses Interface
ICMP redirect cache is empty

For example:

#show running-config | i routing
no ip routing

For example:

#config t
(config)#router ospf 5
IP routing not enabled

no ip route IP NETMASK GATEWAY

Removes the routing for IP NETMASK GATEWAY.

When the no command is used before any other configuration-mode command - it's the way that you tell a Cisco Switch to unset a setting.

For example, no ip route x.y.z.q netmask destination. no router bgp ASN would be fairly disastrous, though - it would take out the "router bgp" clause and all of the neighbor and other statements underneath it.

To delete a neighbor and re-enter it, use router bgp ASN and then no neighbor x.y.z.q.

For example:

(config)# no ip route 192.168.25.0 255.255.255.0 192.168.18.100

ip route IP NETMASK GATEWAY

ip route x.y.z.q NETMASK GATEWAY [metric]

The "ip route" command installs a route to the IP space starting at x.y.z.q and spanning the length specified by netmask, pointed towards gateway as a next-hop. Gatewaycan be an interface name or IP address.

The metric tag is optional (which is why it's shown in brackets). The netmask used to be optional, but no longer is - and even on routers where it is optional it never hurts to be specific!

For example:

(config)# ip route 192.168.25.0 255.255.255.0 192.168.25.1

Summary Script

We can now review a summary command-script that deletes and existing route, adds a new route, shows the route to us, then saves the route to the firmware.

> enable
# config terminal
(config)# no ip route 192.168.25.0 255.255.255.0 192.168.18.100
(config)# ip route 192.168.25.0 255.255.255.0 192.168.25.1
(config)# show ip route
(config)# end
# copy running-config startup-config
# reload