Configuring a Loopback Interface in Cisco

A loopback interface is used for device identification. Although you can use any interface address to determine if the device is online, we recommend using the loopback address. Network topology changes can remove interfaces or change addresses, but the loopback address never changes.

Uses of Loopback Interface:

1. It is used for routing protocols, reachability, and testing purposes. 
2.  It is also used to identify the device while physical ports can also be used to identify the device loopback interface are preferred. 
3.  Protocols like OSPF also use the loopback interface to determine their properties

Configuring a Loopback Interface On  Cisco Router:

Here, you can pick any router of your liking from the router section in the Cisco packet tracer. After picking a router, open its CLI and perform the following steps to configure a loopback interface on a router:

interface loopback 0
ip  add 10.0.0.1 255.255.255.255

Checking Loopback Interface:

show interfaces loopback 0

sh ip interface brief | exclude unassigned

Note:

1. A loopback interface is by default no shutdown.
2. A loopback interface has no MAC address.