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    Configuring a Loopback Interface

    The loopback interface provides a stable address for protocols (for example, BGP, Telnet, or LDP) to use so that they can avoid any impact if a physical interface goes down. The loopback interface sends packets back to the router or access server for local processing. Any packets routed from the loopback interface, but not destined to the loopback interface, are dropped.

    Note: Do not confuse loopback with the null 0 interface. Traffic routed to null 0 is discarded on the line module.

    To access and configure the loopback interface:

    • Issue the interface loopback command in Global Configuration mode.
      host1(config)#interface loopback 20 host1(config-if)#ip address 10.10.20.5 255.255.255.254

      Use the no version to delete the loopback interface.

    Published: 2014-08-12