IPv4 Loopback Interfaces

• The loopback interface is a logical interface that is internal to the router
• It is automatically placed in an “up” state, as long as the router is functioning
• The loopback interface can emulating networks behind the router

Router(config)# interface loopback number

Router(config-if)# ip address ip-address subnet-mask

Router(config-if)# ipv6 address ip-address/bits

Suppose you would like to simulate a link to a network, perhaps while building your LAN to make sure your LAN can get through your equipment to the simulated network. How would you do that?

https://www.youtube.com/watch?v=h3LC_iITL18

Loopback Interface Symbology

Lo 0: 2001:A:B:C::1/64

Examples of Loopback Interfaces in Use