Question regarding loopback interfaces on OSPF

gbdavidx

Stupid newb question alert

IF a link/interface does fail and you have a loop back address assigned to the interface, is the router still able route packets?

networker050184

What do you mean a loopback address assigned to that interface? Like unnumbered? Traffic will still route if there is another path.

gbdavidx

Lets say when you do
!R1(config)#
R1(config)#interface loopback 1

or like what this guy did on youtube

https://www.youtube.com/watch?v=WGbu83IvxXs

networker050184

Loopback interfaces do not go down. That is the point of them! But I am assuming you mean the loopback is the router ID and you manually shut it down. That would not matter. While the router ID is in the form of an IP address, it is not used for forwarding.

gbdavidx

I'm asking about the actual interfaces. Like interface fastethernet 0/1 0/whatever. If that goes down and you have a loopback set will it fall back on the loopback interface if there is no alternate path

networker050184

Still have no idea what you are asking. The loopback is a logical interface that is reachable via any path to the router. It is independent of any physical interface.

Magic Johnson

Are you asking if the physical port fails will the loop back take over??

deth1k

are you sure you are not confusing this with BGP peering using loopbacks?

Adam B

I think he means if lets just say there are two alternate paths to network 192.168.1.0 and both of those links fail, will the loopback then be the next best "path"? The answer to this is no, as the loopback is primarily used for setting a Router ID in OSPF, and even then the loopback has no path to the network as its just a loopback, an interface used for troubleshooting. Any traffic that is sent to a loopback IP address is immediately passed back up the TCP/IP stack as if it had been received from another device. Just a way of troubleshooting once again and making sure you have TCP/IP capability and that the problem isnt TCP/IP.