Configuring a Loopback Interface

Real World Application:

Loopback interface management of common application scenarios, including tunnel interface, the source/destination, network simulation, dynamic routing processes the router ID link, and others. CCNA as you would need in order to be able to create and delete the loopback interfaces from Cisco devices.


This lab will teach you how to configure the loopback interface.

Lab Prerequisites:

If you use GNS3 started free CCNA R1 load Binder GNS3 topology.

Establish a console session of Router 1.

Lab Instruction:

A loopback interface is a software-based "always up" logical interfaces. They will not be bound without any physical interface so they can go unless they are administratively closed.


To create you need to navigate the global configuration mode command interface loop interface loopback interface # creates automatically. Configuration looks like this;

Router con0 is now available

Press RETURN to get started.

Router>enable
Password:
Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#interface loopback ?
    Loopback interface number

Router(config)#interface loopback 1
%LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up
Router(config-if)#

After creating the interface you will see interface changes, open immediately. According to the requirements the goal you see below; on the interface to configure the IP address 10.233.21.251/24

Router(config-if)#ip address 10.233.21.251 255.255.255.0

Loopback 1 target 2 ask us to remove the interface, you can negate the interface command does not use any interface loopback # command, as shown below; remove the loopback interface

Router(config-if)#no interface loopback 1
% Not all config may be removed and may reappear after reactivating the logical-interface/sub-interfaces
Router(config)#
%LINK-5-CHANGED: Interface Loopback1, changed state to administratively down
%LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to down

Once you have deleted the interface you will find that not all configuration may have been deleted, and restart the logical interface/sub-interface may reappear after a warning.

Cisco IOS problem this neighborhood for many years, it has not been fixed. Basically this warning lets you know that if you delete the logical no interface or sub-interface command some of the previous configuration may return to re-create the same interface. If you encounter this problem, router overload will resolve this problem.