[c-nsp] Mac address flapping..

[James Ashton]

Alan,

You guessed it.   The customer had vlan 42 and another vlan tied together in their switch.  That’s where the errors were coming from.


Thanks for all of the ideas.

James



-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of James Ashton
Sent: Monday, July 13, 2009 9:49 AM
To: Mateusz Blaszczyk
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Mac address flapping..

The most confusing thing is..   The Mac that is flapping is the Mac address for the vlan interface (VLan 42 of course) from 6509-b.   But I am only seeing the log entries on 6509-a.


I am looking at the entire path of the vlan now.  Maybe it is patched into another vlan at some point that I am not aware of....    
That would make life SOOO much easier...  If its not.  Then I think I am left with IOS bug...


James

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Mateusz Blaszczyk
Sent: Monday, July 13, 2009 9:07 AM
To: A.L.M.Buxey at lboro.ac.uk
Cc: Lincoln Dale; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Mac address flapping..

Alan,

But why only 1 MAC is flapping?

HSRP sends dest-mac as multicast address so there are clearly 2 paths
between these switches.
Unless the connection is unidrecional somehow, how on earth he doesn't
see same on second 6509-b?

It's confusing.

-mat

2009/7/13  <A.L.M.Buxey at lboro.ac.uk>:
> hi,
>
>
> i originally thought on the same lines too - but then having
> been told this still happens if theres only one link
> to the 4500s to the client - which makes the 6506-b almost
> a router at the end of a stick for that network things started
> to look a little 'wonky'.  it wouldnt be taking traffic from
> another port(?).
>
> as far as i now see, you have 2 routers, A and B.   A has the feed to
> the switch (and the only physical link to the customer) whilst
> B is connected to A via a portchannel and trunk link. a MAC for
> vlan042 is still flipping between the down-link from A and the
> link from A to B.  now, from my deepest memories I've seen this sort
> of thing happen on our campus in the past... i've got some feeling that
> somewhere, that VLAN is being fed into your network as another VLAN
> and therefore the AMC is squirting back out and through - eg native vlan 042
> is patched to vlan 1 or somesuch elsewhere, therefore the MAC is seen
> coming back t;other way
>
> alan
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