Cisco 2950 v12.1(20)EA1a err-disable bug??

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Jun 9th, 2010
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Hi All

We change a CPE router connected to a switch 2950 to a new CPE router. But after the change on teh switch we have :

Jun  9 14:10:35.091: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/5.
Jun  9 14:10:35.091: %PM-4-ERR_DISABLE: loopback error detected on Fa0/5, putting Fa0/5 in err-disable state
Jun  9 14:10:36.091: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to down
Jun  9 14:10:37.099: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to down

when I put back the hold router still same issue.

I can bring up the interface with no keepalive, but still issue with the loop

If I change manually the mac address then the interafce came up, but still not passing any traffic

Any idea?



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Giuseppe Larosa Wed, 06/09/2010 - 07:36
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Hello Melanie,

there is a bug affecting some low end switch platforms with these effects (but  on fiber based ports if I remember correctly)

However, you already have found the workaround that is to disable keepalive on the interface

Hope to help



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