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MAC flapping

Not applicable

First post requesting help, so be gentle.

 

I'm getting MAC flapping errors at one of my remote sites.  I've traced the MAC using the "sh mac address-table address [mac]" command, but it keeps leading me to trunk ports going to other switches - never to an end user port.  IE:

 

3750->SW70->SW72->SW70->SW73->SW70->3750 or

3750->SW100->SW102->SW100->SW103->SW70->3750

All switches are 2960s except for the 3750.

 

How do I find and squish this issue?  I don't have any dual-homed servers on the network, but it is possible an end user is using a hub without permission.

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4 Replies 4

devils_advocate
Level 7
Level 7

Have you looked online to see what manufacturer the MAC belongs to?

It might help narrow down the search at least. 

Do you use Port Security?

BPDUGuard?

I did, but it belongs to some company I've never heard of.  The mac is 0050.b657.d9ce and it is to a device from Good Way Technology Co.  I presume it's probably a USB to ethernet type adapter, but that's purely a guess.

 

We do use BPDU guard which would shut a port if it detects a switch connected to a user port.

Looking at their website, I would say its likely that this is a USB to Ethernet adapter. 

Is it just a single MAC flapping?

Have you looked at the ARP cache on the L3 switch/router to find out the IP address associated to this MAC (assuming it has one)?

#show ip arp 0050.b657.d9ce

Correct, just the one MAC flapping like crazy.  I looked on the L3 switch, but the MAC isn't in the ARP table.