[c-nsp] MAC / CAM flapping problem

[Ge Moua]

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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