Loopback Interface - Cisco IOS


Can anybody let me know why and the reasons you may want to setup a Loopback interface on a Cisco Router?

Thanks in advance.

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The loopback interface is one interface you can count on being up, unless the router is totally dead.  So, it makes a great interface to watch to make sure your router is working.

You can also route undesireable traffic to your loopback (or Null0) and black hole it - route it to nowwhere.

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A good example of the use of a loopback interface would be in an OSPF (Open shortest path first) scenario. OSPF can use a loopback address to indentify itself.
Here is an excellent read for you to get a better understanding;

Even better, when using BGP it's best to have routers neighbor up using their loopback interfaces.  That way, the underlying OSPF/IS-IS/EIGRP/RIPv2/static topology can change, and as long as connectivity is possible the BGP session will stay up.
hi, there

Another reason is you could connect the Routers back to back using the null Modem Cisco cable and use the loopback if the origional link goes down and still get access assuming telnet is enabled on the loopback interface.

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