MAC address flapping in and out of MAC table on 3750X stack

[branfarm1]

Hi,

I've noticed that a small number of hosts on one of my 3750x access switch stacks are having their traffic flooded out all ports on the stack. When I focus in on one particular host, the problem is similar to this discussion where the MAC address for the PC is flapping in and out of the MAC table.  I've double checked the spanning tree stability as was recommended in the other thread, but my STP instances appear to be stable.   

Can anyone recommend other steps I can take to identify the cause of the issue?

Thanks,

Brandon

[Leo Laohoo]

Post the complete output to the following commands: 

1.  sh version; 

2.  sh interface trunk; 

3.  sh etherchannel summary

4.  sh logs

[branfarm1]

Here are the requested outputs.

This is a stack of four 3750X, connected to a pair of 4500-X in VSS.

[Leo Laohoo]

"sh log" is useless because it contains SSH debug output.  

[branfarm1]

That's not necessarily true -- It covers about 8 hours of time and while the log only contains SSH information, it also *doesn't* contain any other obvious issues -- MAC Flap notifications, link up/downs, etc.  I checked again this morning and it hasn't logged anything since yesterday when I grabbed the output.

[Leo Laohoo]

Ok, but MAC address flapping can go be seen in multiple switches.  If MAC address flapping isn't evident in the logs then where is it?  The reason why I want to see this vital information is because I want to see the uplinks that are in the error message.

[Leo Laohoo]

Ok, but MAC address flapping can go be seen in multiple switches.  If MAC address flapping isn't evident in the logs then where is it?  The reason why I want to see this vital information is because I want to see the uplinks that are in the error message.

[branfarm1]

Just wanted to provide an update --  I opened up a case with TAC and worked with an engineer to try and find the cause of the issue.  The TAC engineer was unable to identify the cause, mostly because the usual suspects for mac flapping were not present.  We agreed to a reboot during a weekend change window and since the reboot everything has been working fine.