Assign or configure IP addresses on Cisco routers

Contributed by qmchenry May 25, 2006  
Tagged: Cisco router

Every active interface on a Cisco router to be used with IP requires an IP address assigned to it. This short recipe describes how to set an interface’s IP address.

Given an interface fastethernet1, the IP address 192.168.1.5 with the subnet mask 255.255.255.0 can be assigned to it using the following command from privileged mode:

Router(config)#interface fastethernet1
Router(config-if)#ip address 192.168.1.5 255.255.255.0
Router(config-if)#no shut

The last command is important. It is an abbreviated form of “no shutdown.” The default state of an interface is “shutdown” which makes the interface administratively down. If you plumb up an interface and it doesn’t work, check to make sure it isn’t administratively down first.