CompTIA® Network+ Lab Exercise : Configuring Loopback Interface

8. Configuring Loopback Interface

Description: The purpose of this exercise is to configure a loop back interface and test it for connectivity. The loopback interface is a logical interface internal to a router. It is not connected to any other device. A loopback interface is UP as long as the router is up and running. It is useful in managing a router as there will always be at least one interface available on the router, irrespective of other physical interfaces.

The command used for assigning loopback interface is:

Router(config)#interface loopback <number>

The number can be between 0 and 2147483647

A loopback interface is automatically put in "no shutdown" state when created. However, you need to assign an ip address to use a loopback interface.

Network Diagram :

Configuring Loopback Interface daigram


1. Configure s0 on R1 with ip address and subnet mask as shown in the diagram

2. Configure s0 and loopback 1 on router R2 as shown in the diagram

3. Ping loopback 1 and verify connectivity

R1#configure terminal
R1(config)# interface serial 0
R1(config-if)#ip address
R1(config-if)#no shutdown

R2#configure terminal
R2(config)#interface serial 0
R2(config-if)#ip address
R2(config-if)#no shutdown
R2(config)#interface loopback 1
R2(config-if)#ip address


Type escape sequence to abort.
Sending 5,100-byte ICMP Echos to ,
Timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/6/6 ms

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