[c-nsp] Mac address flapping..

[Lincoln Dale]

its either a loop, or the server in question is dual homed with the same 
mac address on two physical switches.
since your network hasn't yet melted down because of a loop and 
loopguard (which you have enabled right?) hasn't seen a BPDU on a port 
which shouldn't ever receive them, my money is on a host that is 
misconfigured.

e.g. think of the host using the equivalent of a portchannel mode 'on' 
and balacning traffic both directions.
your switching infrastructure will see this as a mac-move.

this is not a valid scenario for a host.  the host either needs to be 
connected to:
 A. a single physical switch with all physical interfaces configured 
into a port channel such that the switch sees it as a single logical link
 B. plugged into multiple physical switches (for redundancy) with the 
switches supporting multi chassis ether channel (MCEC).

for (B), the only valid scenarios at this point in time are:
    Catalyst 6500 VSS
    Nexus 7000 virtual Port Channel (vPC)
    Catalyst 3750 switch stack


cheers,

lincoln.



James Ashton wrote:
> I have looked at all the port configs in question.    No forgotten stuff that I can see.
>
> I am willing to go with the loop idea..  But I dont get any loop errors.   I dont get any Mac Move errors other than for this HSRP Mac Address, and over 120 other vlans on  these same ports arent having this issue.
>
>
> But if it were a loop, how would I find it and fix it..   I ahve gone through every method I know of and allt he Cisco troubleshooting docs.   I can feel that I am missing something here, But I just cant think of what.
>
> James
>
> ________________________________________
> From: Mateusz Blaszczyk [blahu77 at gmail.com]
> Sent: Friday, July 10, 2009 3:19 PM
> To: James Ashton
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Mac address flapping..
>
> James,
>
> . (I have a pair doing redundant gateways for a DataCenter network)
>   
>>       %MAC_MOVE-SP-4-NOTIF: Host 00d0.009e.2400 in vlan 42 is flapping between port Po1 and port Gi1/7
>>
>> I see about 20 of these for this one vlan each minute.
>>     
>
> the mac is 6509-b and pps==20/minute is probably HSRP hello packet
> from Vlan42 on 6509-b.
> if there are no topo changes in stp there must be a unnoticed L2 loop,
> either forgotten portfast or bpdu filtering between 6509-a,-b and
> 4506-a.
>
> perhaps try to disconnect the customer completely during a maintenance
> window and double check all your connections.
>
> Best Regards,
>
> -mat
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