EIGRP loopback interface

I am currently working through my routing protocols and I keep seeing references to ip loopback addresses.

What is the point of having loopback addresses configured in terms of routing?

Thanks

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Comments

alan2308

The main thing is that EIGRP and OSPF use the highest Loopback IP address as the router id if you didn't manually set a router id.

APA

loopback interface is not a physical interface... so theoretically the interface should always be up and available, thus meaning if you have multiple paths to a router losing a single physical interface\path should cause less of an impact depending on your topology.

APA

would extrapolate more but I'm on my mobile and the post would turn into one mega paragraph.... and hard to read

Selfmade

alan2308 wrote: »

The main thing is that EIGRP and OSPF use the highest Loopback IP address as the router id if you didn't manually set a router id.

correct, it also provides stability for the OSPF election process, kind of like how bridges determine who is the root bridge. Routers use something similiar with loopback interfaces with EIGRP and OSPF, with OSPF, the loopback interface serves as a router id for the election process. OSPF priority is another way to set the election process in a way you want it to happen.

Also for the OSPF and EIGRP labs for CCNA you will often see the loopback interfaces, they are usually there to simulate an ISP router or a router that is not inside the local network.

chmorin

Only a basic understanding of how a loopback interface works with routing protocols like OSPF and EIGRP should be needed for the CCNA level. If you plan on hitting CCNP, loopback will start to be brought up more often.

Generally all alan2308 said is all that is significant to CCNA, but knowledge is power!