[c-nsp] MAC / CAM flapping problem

[Bill Wichers]

I'll have to look a the code update. For now I set a permanent MAC entry
for the router and now instead of all the "flapping" messages it just says
it heard something from a permanant MAC address but on the wrong port, and
that message doesn't come with traffic interruptions like the earlier
error did.

     -Bill

> Had the exact same thing happen to me on a 2948G L2 switch which I think
> uses the same CAT4k software.  Anyway, solution was to update the CatOS
> firmware and reboot.  Actually a reboot fixed it but the update kept it
> from happening again.
>
>
>
>> -----Original Message-----
>> From: cisco-nsp-bounces at puck.nether.net
>> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ge Moua
>> Sent: Monday, July 17, 2006 4:59 PM
>> To: 'Bill Wichers'; cisco-nsp at puck.nether.net
>> Subject: Re: [c-nsp] MAC / CAM flapping problem
>>
>> There were bugs in older CatOS code that caused similar
>> symptoms as you described this.  This may no longer be the
>> case with the newer CatOS software.
>>
>>
>> :-)
>> Regards,
>> Ge Moua | Email: moua0100 at umn.edu
>>
>> Network Design Engineer
>> University of Minnesota | Networking & Telecommunications Services
>> 2218 University Ave SE | Minneapolis, MN 55414-3029
>> Office: 612.626.2779 | Pager: 612.###.#### | Fax: 612.626.1818
>>
>> -----Original Message-----
>> From: cisco-nsp-bounces at puck.nether.net
>> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Bill Wichers
>> Sent: Monday, July 17, 2006 6:21 PM
>> To: cisco-nsp at puck.nether.net
>> Subject: [c-nsp] MAC / CAM flapping problem
>>
>> I have a Catalyst 4000 with several trunks to other switches,
>> and I've been seeing a lot of this message:
>>
>> 2006 Jul 17 19:07:39 edt -04:00 %SYS-4-P2_WARN: 1/Host
>> xx:xx:xx:xx:xx:xx is flapping between port 2/6 and port 2/4
>>
>> Where all the xx:xx: stuff is the MAC address of the gateway
>> out, which is on port 2/4. Port 2/6 is an uplink to another
>> switch with some 100+ servers on it.
>>
>> I've checked and there is no loop in the network (everything
>> stars out from the 4000), and the other switches are
>> unfortunatly not Cisco (yet, we're replacing them) so I have
>> limited diagnostic tools available on them.
>>
>> The problem I'm having is that every time the flapping occurs
>> it causes a burst of packet loss, presumably while the switch
>> relearns the correct MAC address on the correct port. Both
>> ports are 802.1q trunks carrying numerous VLANs. I was
>> looking at port security, but the docs imply that it can't
>> work on a trunk.
>>
>> Does anyone know of a way to force the switch (running CatOS
>> v8.1(3)) to ignore the routers MAC address if it hears it as
>> a source address on any port except 2/4? I can't seem to find
>> a way to do it that will work on the trunk ports AND will
>> still allow traffic to pass to the router using the router's
>> MAC address as a destination.
>>
>> Any help much appreciated!
>>
>>      -Bill
>>
>> *****************************
>> Waveform Technology
>> Systems Engineer
>>
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*****************************
Waveform Technology
Systems Engineer