Flapping ports

[Andrew White]

Hello,

Flapping ports in my experience is normally to do with a loop or dodgy cable.

Can someone back sense of this flap and why so many ports/mac addresses?

This is from a 3750 the root switch which has a trunk to a 2960 on 2/0/11 and I see this from time:

And on the other end of the the trunk on the 2960 I see this:

Gig 0/24 is the trunk port back down to the 3750.  Does it look like what ever is on Gig 0/2 is causing the issue?

If so why does the 3750 then flap on most of it's ports after?

[balaji.bandi]

check what is the device connected to that port by using show cdp neigh

Check the network switches for misconfigurations that might cause a data-forwarding loop. 

check spanning-tree configuration.

[Andrew White]

Sh cdp and spanning tree look as they should.

could a look on a device beyond the 2960 cause this flap and if so why would ports on the 3750 flap too?

Setup

3750------->2960------->3 ports going  to 3rd party LAN

[balaji.bandi]

Post the configuration to have a look for what is wrong in the configuration.

is this working and having issue recently or have you had any changes recently which causing the issue

[Leo Laohoo]

MAC flapping is a sign that Etherchannel is not configured properly.