Loop back

Unanswered Question
Dec 11th, 2007

what ip address i can use for Loop back intf.? Up to how many Loop back i can use? Should the ip address follows the same subnet as with my physical interfaces? thanks!

I have this problem too.
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Hi, the loopback address is logical interface within to your switch or router, with that said the good thing it can have any valid IP address assigned to it. not to be confused with the loopback address, the loopback interface can be included in routing protocols and function like any interface, once you configure your loopback interface it will be up and up and yes you can configure multible lookback interfaces.



Configuring a Loopback Interface: Example

The following example indicates how to configure a loopback interface:

RP/0/RP0/CPU0:router# configure

RP/0/RP0/CPU0:router(config)# interface Loopback 3

RP/0/RP0/CPU0:router(config-if)# ipv4 address

RP/0/RP0/CPU0:router(config-if)# end

Uncommitted changes found, commit them? [yes]: yes

RP/0/RP0/CPU0:router# show interfaces Loopback 3

bvsnarayana03 Tue, 12/11/2007 - 21:16

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.

pls refer this link:


hope that clarifies.

pls rate all helpful posts.

Richard Burts Wed, 12/12/2007 - 07:41


Other responses have addressed the usefulness of the loopback interface and addressing on the loopback interface but not the aspect of now many loopback interfaces you can have. The number of loopback interfaces is limited by the number of IDBs on your router. Each interface, including loopbacks, requires an Interface Descriptor Block. The number of IDBs varies by platform and by version of code. You can find how many IDBs your router supports in the output of the command show idb.




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