catalyst 3550:Support for keepalive loopback issue

[jpmanrique]

Hi,

I am trying to confirm if the message shown below is strictly associated to a physical loop in the platform Catalyst 3550 or maybe this message could be showed when there is a Spanning tree problem.

%ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on GigabitEthernet0/1

I have navigated by the CCO but I am not able to find the exact message description. Mainly I am interested in the 'keepalive packet' characteristic.

On the other hand, I do not understand why there is no any spanning tree log associated when the loopback is detected.

I will be grateful if someone can explain me these issues.

Thanks

[cosimig]

I have experienced the same thing. Cisco says to check cables and gbics. I have done that.

My 3550 is connected to a 2950. When I went over the configs of both, I found that keepalive was set differently on each interface.

I have turned off keepalive on the 2950 (the other end) and the 3550 by issuing the no keepalive command.

This seemed to resolve the issue.

I sure would like someone from Cisco to explain why that might be.

[jpmanrique]

Thanks for your help.

Unfortunately I need to know if this kind of message describes a physical or level 2 loop. I am pointing out this because I suffered a broadcast storm in the other end. However, I have not seen any spanning tree message.

[gcelauro]

I have experienced the same thing with 3550-12G at core and 3550-24-EMI or 3524-XL at the edge. I found the problem only over new switches (3524-XL does not detect the problem)

[ankurbhasin]

Hi Jpanrique,

These messages are not at all related to STP or layer 2 loop. It is just a keepalives sent back to itself with its own address as the source address. It is also associated to the bug. The best workaround is to disable the keepalives on the interface.3550 is hitting a bug with this on gigabit interface.

Keepalives are much more required for router interfaces and are not of use between layer 2 switchports.

Ankur