http://tech-recipes.disqus.com/Cookbook of Tech TutorialsenFri, 27 Jun 2008 07:04:05 -0000http://www.tech-recipes.com/rx/2019/dark_secrets_of_loopback_addresses_cisco/#comment-2770609I don't know quite where to start with this but if you're looking for info I'd suggest looking elsewhere.<br><br>First, loopbacks don't have much to do with troubleshooting. You can ping one or use it as the source for pings but you can do that with any interface with an IP. <br><br>Loopbacks are often used for router management but can also be used to provide virtual interfaces for things like GRE tunnels. The reason you use a loopback is that a physical interface can go down but the loopback, being virtual, is up as long as the router is up.<br><br>Regarding OSPF, the term "feasible successor" is from EIGRP, it's not used in OSPF. I think the author was looking for is Router ID. This the IP the router uses to identify itself to other routers running OSPF. The router is determined thusly:<br><br>1 Use the address configured by the ospf router-id command<br>2 Use the address of the loopback 0 interface<br>3 Use the highest IP address of any interface<br>4 If no interface exists, set the router-ID to 0.0.0.0AWfkiFri, 27 Jun 2008 07:04:05 -0000