Inexplicable Error Disable

[Translator]

Configuration

C9300X ⇔ WS-C4500 ⇔ C9500 ⇔ 2960X

event

A loop occurred between C9300X and WS-C4500, and error-disabled on WS-C4500.

Unplug the C9300X optical cable, and restore it with no shutdown on WS-C4500.

I thought that error-disabling was stopped at WS-C9500 and that there was no other effect.

The 2960X uplink under the C9500 was error-disabled and communication was stopped.

I expect the loop packet on the WS-C4500 to stop.

Is it possible to fly to 2960X?

[Enes Simnica]

gDay to u. So, what happened here makes sense. Even though the loop was directly between the C9300X and the WS-C4500, the broadcast or loop traffic can still propagate further into the network before the error-disable takes effect. The 4500 may have forwarded some of that storm traffic toward the C9500, which then pushed it down to the 2960X.

So yes, it is possible for those loop packets to “fly” down to the 2960X and cause its uplink to go into error-disable. Error-disable is a local protection, it doesn’t stop packets from traveling elsewhere until the affected interface shuts down.

And my Cisco friend, if u want to avoid this kind of side effect in the future, features like storm control, BPDU guard, or loop guard on access and distribution links can help contain loops before they spread too far.

hope it helps and PEACE!

-Enes

[MHM Cisco World]

This chain of SW there is no loop.

Loop can only happened if your fiberoptic is unidirectional.

So first we need to check fiberoptic' are you run udld or not ?

MHM