In order to set up an IP address on an interface, we need to be in the interface level of the command line. This is a level within the global configuration level. From global configuration mode, we can enter the ‘interface serial 1/0’ command. If you are unsure of what interfaces are on the router, you can use “show ip interface brief” or “show run | in Serial”.
The command to set the IP address, once in interface mode, is ‘ip address x.x.x.x z.z.z.z’ where x is the IP address, and z is the subnet mask. All interfaces on a router, by default, are in a shut state (off), to turn the interface on, we use “no shut” and similarly to turn it off again “shut”. Once the IP has been set, you can confirm the interface is live and that the IP has been accepted by using ‘show ip interface brief’. You will notice in the live demo below, that my interface was Serial 1/0 and the interface is now in a UP UP state.