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What is the use of Loop Back Interfaces on a Cisco Router??

We can configure number of loop back interfaces on a router, but please tell me the exact use of those interfaces??????

Articles About Routers

This entry was posted on Friday, January 22nd, 2010 at 11:24 pm and is filed under Cisco Router. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

2 Responses to “What is the use of Loop Back Interfaces on a Cisco Router??”

  1. A loopback interface is ALWAYS active and CANNOT fail, that is the reason they are used, they are always in the up/up state and this makes routing protocols such as OSPF and BGP much more stable, as opposed to using a real interface.

    In addition, some routing protocols like OSPF will use the highest IP address configured on the router as the router ID, but you can override this behavior by configuring a loopback address.

    Finally, you can use the loopback address as the "source interface" for traffic that is generated by the router, such as syslog packets, SNMP traps, and security related packets.

    A typical config file’s loopback related commands might look like this:
    interface Loopback0
    ip address 172.16.1.1 255.255.255.255
    router ospf 100
    router-id 172.16.1.1
    ip tftp source-interface Loopback0
    ip tacacs source-interface Loopback0
    logging source-interface Loopback0
    snmp-server trap-source Loopback0

  2. Lord_of_Armenia on January 22nd, 2010 at 11:24 pm

    Some virtual networking applications use loopback connections to make a computer think that its connected to a network when it is really just connected to itself.

    There are probably other uses as well.

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