[c-nsp] MAC / CAM flapping problem

[Charles J. Boening]

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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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