Question

Port flap on LACP load sharing group causes permanent network loop


Had a neat issue that killed our network the other day. Tracked it down to a flaky port on a single switch that was connected to a stack with LACP. I was able to reproduce the problem.

Take a stack and LACP load share one port from each stack member to 2 ports on another switch, send some multicast traffic across it (VRRP or ELRP is enough), then unplug and plug in one of the ports several times.

Eventually, the LACP link will stop forwarding within the confines of the algorith and it turns the ports into a big L2 loop. Doesnt seem to happen with static sharing, just LACP. Reproduced on x450e-48p, but appears to happen on x460s as well, 15.3.3.5p1-2

3 replies

Userlevel 4
Please call the TAC and report the bug.
Case open for 3 weeks.
Userlevel 4
Can I have case number?

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