ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected

Unanswered Question
Mar 26th, 2009

Yesterday we had a situation with two switch stacks going down. The logs showed the following message ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected. To resolve the issue we had to shut then no shut the ports which had error disabled. I understand the keepalive packet is looped back to the port that sent the keepalive. What would be the best method to determine the device that has caused this loop? We have rapid-pvst enabled on all our switches.

After looking at the logs of some of the other switches which we use to connect to our other site I've noticed the following messages.

%C4K_EBM-4-HOSTFLAPPING: Host 08:00:0B:EE:28:69 in vlan 12

Could these errors be related?

I have this problem too.
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Giuseppe Larosa Thu, 03/26/2009 - 04:09

Hello Darren,

1) what devices and versions are the components of the stack ?

there is a bug related to switches considering a loop the fact they receive their own keepalives on fiber based ports.

I mean that ethernet keepalve work exaclty in this way: it is right to receive back your own keepalive messages because they have mac dest = local port MAC address.

2) %C4K_EBM-4-HOSTFLAPPING: Host 08:00:0B:EE:28:69 in vlan 12

it can be related.

Hope to help


darrenriley5 Thu, 03/26/2009 - 04:40


IOS 12.1(14)EA1a

Yes we are using fiber based ports for the trunk links.

Would you recommend disabling keepalives on the trunk links/

Giuseppe Larosa Fri, 03/27/2009 - 07:33

Hello Darren,

the suggested workaround in the bug description was actually to disable keepalive on fiber based links

I'm not sure your device is affected but you could make a try if STP is enabled

Hope to help



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