cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
595
Views
0
Helpful
6
Replies

Wierd MAC Flapping Errors

c2jkeegan
Level 1
Level 1

We had an issue with a MAC flapping in our network today. We've dealt with this before and for the most part have eliminated it with BPDU guard.

Today's MAC flapping seemed different since instead of a bunch of different MACs flapping between their port and the port towards the loop. Something like below with Gi1/32 being the port towards the loop:

%C4K_EBM-4-HOSTFLAPPING: Host AAA in vlan 100 is flapping between port Gi1/1 and port Gi1/32

%C4K_EBM-4-HOSTFLAPPING: Host BBB in vlan 100 is flapping between port Gi1/2 and port Gi1/32

%C4K_EBM-4-HOSTFLAPPING: Host CCC in vlan 100 is flapping between port Gi1/3 and port Gi1/32

We saw the same MAC flapping between many “Access Ports” and the port towards the loop. Something like this:

%C4K_EBM-4-HOSTFLAPPING: Host XXX in vlan 100 is flapping between port Gi1/1 and port Gi1/32

%C4K_EBM-4-HOSTFLAPPING: Host XXX in vlan 100 is flapping between port Gi1/2 and port Gi1/32

%C4K_EBM-4-HOSTFLAPPING: Host XXX in vlan 100 is flapping between port Gi1/3 and port Gi1/32

The former case make sense to me since frames with the MAC addresses of the hosts on ports Gi1/1-3 get forwarded down Gi1/32 got looped and come back to the switch. But the case we saw today make no sense to me since ports Gi1/1-3 are not loops and do not have hosts with MAC address XXX on them.

It's still not clear how this loop happened, but it looks like something to do with a host with two NICs with unknown OS or config.

Can anyone shed any light on how we could have seen the behavior we saw today?

Thanks,

Joe

6 Replies 6

Hello,

is this maybe a problem in a link aggregation configuration?

Or, we had this problem on Ports where a Access Point was connected to..

best regards, Sebastian

Yes, I've seen that site, but I believe that only explains the first scenario in my post (i.e. Different MAC addresses showing up in the messages).

If this does explain the second scenario, I must be missing something, and I was hoping someone could explain.

Thanks.

Hi,

As s.helmer said. This situation occurs if you have access points where the clients are roamming. Is this the case?

This is not the case, No APs involved.

As I mentioned in my post the loop was caused by a system with two NICs and the other ports were just normal access ports with either a host, a host and phone or just a phone attached to them.

Maybe it would help to give us a short overview which device is connected to which port..

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: