LoopBack Interface command on routers???

[ewieczorek]

Hello everyone! I have a WAN that comprises of 32 sites throughout the state of Nebraska. Each site has a 3725 series router.

I was at a conference and someone asked me if I made use of the loopback interface on my routers. I told him I didn't know much about this command on the router. I was then told that I should consider using the LoopBack Interface command on my routers. This person didn't really go into much detail for me after that.

Could someone provide me with some general information about this? Why would one use it? What's the benefit? Any general thoughts....

Thank you!

Eric

[bratager]

Basically, the loopback interface is a virtual interface that you configure on the router. Being a virtual interface, it never goes down unlike physical interfaces so as long as you have one physical interface reachable on your router, you should be able to reach the loopback. This makes the loopback ideal for things such as network management traffic and DLSW. Also, routing protocols such as OSPF and EIGRP use the loopback address for the router ID so using a loopback interface gives you better control of the router ID and allows for easier administration.

[thisisshanky]

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080087093.html#1012526

http://www.aarnet.edu.au/engineering/resources/bgp/loopback-6up.pdf

These links might help!

[ewieczorek]

I appreciate all the info.

These remote routers have only one connection to the WAN on S0/1. So, it's safe to assume that if S0/1 goes down, and the WAN link is still up, I won't be able to hit the loopback interface because I don't have a second serial interface connection to the WAN?

This loopback interface would probably work best in scenarios where the network admins have multiple paths to "touch" the routers? In my scenario, I only have the one WAN link...

Thanks!

[ruwhite]

Yes, this is correct. Loopbacks are most useful where there are multiple physical connections available, and you want a single IP address on the router which is reachable regardless of which specific physical connection is available.

:-)

Russ.W

[ewieczorek]

Thank you for all the info!