Loopback Interface

Question

I have been going back and forth with my ISP who manages all my MPLS routers. Right now I am polling the internal LAN interface for SNMP with Orion. I asked them the question about giving me SNMP access to the loopback interface so when a site goes down I can have more accurate alerting telling me if it was the LAN side or T1 side that is down. right now if I get an alert of a site being down I have no idea if it's a WAN issue or internal LAN issue. They claim that using a loopback will not benefit me this way. I thought it would????? I guess I'm looking for some clarification on this.

ecklerwr1 · Answer

I think I can say for most it's a best practice to monitor devices from a loopback interface that's always up and doesn't change.

FormerMember · Answer

what I may do is move my SNMP polling to the serial interface instead of polling the internal LAN interface. That way i can at least get an alert on the LAN side if the WAN is still operational.

extrands · Answer

Your ISP does, and does not have a point.  If the WAN side interface goes down, and you do not have an alternate path back to Orion, you would not be able to tell the cause.  If the problem were with the LAN side interface, managing from the loopback would make sense, as the WAN side would still be up, and you would alert on the LAN being down.  In my experience, WAN failure is far more likely than LAN, so without an alternate path, you might not be buying too much.  That said, I much prefer to tie SNMP to a loopback rather than a physical interface, as most of our locations do have alternate routing available.