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MAC Flap on 3750 L2 Switch

(See attached picture)
I have a 4948-10G acting as a Router for my customers Gateway on Vlan 51
I Trunk Vlan51 and several others to a 3750-12S for GIG SPF L2 aggregation.
from there, I trunk the exact same Vlans to a 3560, and 2 3400M switches for L2 endpoints.

my problem is that i constantly get this syslog message from my 3750-12S:
SW_MATM-4-MACFLAP_NOTIF: Host 001f.ca74.977f in vlan 51 is flapping between port Gi1/0/1 and port Gi1/0/12
Port 1/0/12 is my trunk back to the 4948-10G, and port 1/0/1 is my trunk to the 3560.
the mac address in the log message is the mac address of the VLAN interface on my 4948-10G.

I have absolutely no problems network wise that would indicate that this is a problem. I would like to fix the issue so that my syslog is clean. In all common sense, I would think that it would be NORMAL for the 3750 to see that mac address on both ports, and actually see it on the other two ports going to the 3400M's also but I don't. any ideas??

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Dmapros

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SOLUTION

Don Johnston

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HunTelWebProgrammer

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these switches reside in separate towns several miles apart, I would know if they were connected to each other twice because i would be using more than 1 pair of fiber between towns to get to them. (small detail i forgot to mention, sorry) CDP neighbors are clean, and I have spanning-tree blocked on all trunks for this leg of the network, spanning tree is only enabled on the 10G trunks on the 4948 that is not part of this equasion. Also, since i have no network issues, a loop is unlikely. we have never used 3750's before in our network, and was wondering if there was just something special i needed to do to it for my specific application. again, the message in syslog I get (stated above) sounds legit, i would think the switch would see the gateway of vlan 51 on ALL its trunk ports. would changing the management VLAN on the 3750 to something other than 51 solve my syslog messages you think??

SOLUTION

Don Johnston

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HunTelWebProgrammer

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i changed the management interface to a different subnet, and it went away. there was no loop.

HunTelWebProgrammer

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the network loop was not my issue.