Logs showing loop on uplink ports only

[Jason_Hilt]

On almost all of my network closets I am getting:
Slot-1: [CLI:Voice-Vlan:3] LOOP DETECTED : 94547 transmitted, 935607 received, ingress slot:port (1:49) egress slot:port (1:49)

It always shows the vlan we use for ip phones and the uplink ports. Only difference is sometimes it shows CLI:Voice-Vlan:2 instead of CLI:Voice-Vlan:3.
We have ELRP setup on all ports with 1:49 and 2:49 uplinks excluded. Those are setup in a LACP LAG, which for many of the switch stacks quit working and won't reconnect.

Is there anyway to find out what other port or ??? is causing the loop? Bandwidth isn't an issue on any of the switches. All are less than 1% so there isn't any network storm.

[BrandonC]

'show switch | inc MAC' will get the MAC address for you. When I said 'broken', I meant as in split up to be used elsewhere without being reconfigured, not necessarily in a broken state. If you aren't seeing any network issues, I wouldn't expect that there is anything seriously wrong with the stacks.

Regarding ELRP on the core, I'd just do the voice vlan for now. Ultimately, it may not be a bad idea to run it on all the VLANs, but for now I'd stick with the ones that are reporting loops on your edge switches.

[BrandonC]

I've seen this before when a stack gets broken up but not fully reconfigured, and you end up with two stacks that are both using the same MAC address. Then they see each other's ELRP packets (sourced from a MAC that they think they own) and assume it is their own ELRP packet (logging it as a loop).

It may be worthwhile to check the stacks that are reporting this to ensure that they are not using the same MAC address.

Another thing that may be helpful is to turn on ELRP on the core (but do not configure it to disable any ports). That way, you can at least see if it tends to point towards one particular edge switch.

[Jason_Hilt]

That was my first thought, but the loop is only showing on the voice vlan, which is tagged, and not the untagged computer lan. The voice vlan doesn't traverse the PC port on the phone, only the computer vlan does, so if the cable was plugged back into the wall or even a soho switch plugged in the only lan that would connect would be the untagged computer lan.
I'll look through the switches and see if any are running with high bandwidth.

[EtherMAN]

Odds are a VOIP phone has lan cable plugged back into a hot lan port or a user brough in a small switch and plugged that into the lan side of the phone and another switch port..so the storm is only 10 /100 Mbs... Look on your edge switches and find a port where TX and RX are maxed out or equal... this would be your loop... finding small loops in a multi-ten gig core network is always fun.

[Jason_Hilt]

The path leads back to the core switch on all of the edge switches. We aren't running ELRP on the core since it doesn't not handle any connections other than switches. Wouldn't do any good since all the uplinks would be excluded.