03-09-2009 05:18 PM - edited 03-06-2019 04:29 AM
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 âAccess Portsâ 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
03-09-2009 11:00 PM
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
03-09-2009 11:02 PM
Once again..
maybe this site helps you..
03-10-2009 08:13 AM
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.
03-10-2009 04:38 PM
Hi,
As s.helmer said. This situation occurs if you have access points where the clients are roamming. Is this the case?
03-10-2009 04:45 PM
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.
03-11-2009 12:58 PM
Maybe it would help to give us a short overview which device is connected to which port..
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