Whats the purpose of the LoopBack Int.

[sdross]

Could someone explain or direct me with a link to the purpose and possible real world uses of the loopback interface.

Assume that I have two routers connected by a T1. Is there a benefit to assigning an IP to the loopback int. at the remote end? Do I still need an IP address on the Serial 1 int. at the remote end? What other issues are there? Thanks

[thisisshanky]

Loopback int is a software only interface, which remains always up, unless the router goes down. There are lots of adv. for this type of interface. One use is stability in a connection ( such as BGP connection, OSPF virtual link) etc. When you use loopback interface for the above mentioned connections, and if two redundant paths exist between the two routers, even if a physical link fails in between the routers, the connection wont go down, because an alternate path to the loopback interface exists.

You can also use loopback interface for providing ip address to unnumbered interfaces, which is a method of saving ip addresses.

HTH

[sdross]

Thanks.

So if this router is an end point device, there isn't that much of a reason to use the loopback if there is not a redundant path, is this correct?

[thisisshanky]

There is, another use, say suppose you are running OSPF across the link, the router id of OSPF for each router will be the loopback interface. IF you plan to choose a physical interface ip addfress as router-id, for each time the link flaps, the OSPF neighbor relationship and database exchange is repeated. If you use a loopback interface in this situation, loopback interface never goes down. Thus u can maintain a stable connection. Use of loopback interface, is variable and optional, you may or may not want to use it in your network.

[sdross]

Thanks