Host flapping between port

Unanswered Question
Nov 20th, 2008

Hi All,

I have spent quite long to fix the flapping port, How to fix this problem?

---------from the log------------

Nov 15 11:47:52 CCT: %C4K_EBM-4-HOSTFLAPPING: Host 00:13:E8:73:5A:47 in vlan 66 is flapping between port Gi1/13 and port Fa3/12

Nov 17 12:11:12 CCT: %PORT_SECURITY-2-PSECURE_VIOLATION: Security violation occurred, caused by MAC address 000e.5308.f3bd on port FastEthernet3/4.

Nov 17 12:31:48 CCT: %C4K_EBM-4-HOSTFLAPPING: Host 00:1D:E0:8B:8E:99 in vlan 62 is flapping between port Fa3/10 and port Gi1/17

Nov 17 15:05:17 CCT: %C4K_EBM-4-HOSTFLAPPING: Host 00:16:6F:60:DE:AB in vlan 62 is flapping between port Gi1/15 and port Fa3/10

Nov 17 18:40:16 CCT: %C4K_EBM-4-HOSTFLAPPING: Host 00:1B:9E:AB:C3:F7 in vlan 62 is flapping between port Gi1/17 and port Fa3/10

Nov 17 20:35:19 CCT: %C4K_EBM-4-HOSTFLAPPING: Host 00:16:6F:60:D5:8E in vlan 66 is flapping between port Gi1/13 and port Fa3/12

-- cut --


I have this problem too.
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johnlloyd_13 Thu, 11/20/2008 - 07:17

you should have a good idea of your network topology in order to do this. issue a showmac-address-table address of each host that were flapping based on your syslogs. Try to disable them manually or do a shutdown on the interface connected to it. This might be due to several things. one of them is a virus attack or someone connected a host which shouldn't be allowed, based on port security violation you had on your syslog.

John Blakley Thu, 11/20/2008 - 07:25

This can also happen when you have wireless access points and the client is roaming between them. Make sure that you're not overly redundant on your switches because I just went through this. After cleaning up, I don't see flapping at all.


sam_manay Thu, 11/20/2008 - 07:51

Thanks John,yes at the access switches we put many APs.What do you meant by "after cleaning up"?


John Blakley Thu, 11/20/2008 - 08:02

We had multiple redundant links between switches, and then the servers were connected to each switch. It was a mess. I removed many of the links and left only two.

Do you have all of your SSIDs in the same VLANs across the ports? In other words, do you have it like:

guest - vlan 100

secured - vlan 105

If that's the case, and the access points are all configured this way, you shouldn't see a flapping I wouldn't think. I would verify that it's an access point in these ports that are flapping, and then work backwards from there.


vinayak2010 Tue, 09/09/2014 - 02:32

Hi John,


We are also having simmiler issue. WiFi users MAC moving between different Wireless controllers (as different APs registered on different controller) causing High CPU on 4506 switch (where WiFi VLANs created & Controllers are connected) nearly 98% .

What can be done to avoid this ?

Walter Astori Tue, 09/09/2014 - 03:14

I don't know if this information can help you, but if you set the mac address table aging time to 1 second ? (mac address-table aging-time 1)

ullasupendran Thu, 11/20/2008 - 07:53

hey sam

If you have your wireless access points in VLAN 62, then u dont need to worry abt this flapping. This is due to the roaming of users between the accespoints.



ahmad82pkn Wed, 10/03/2012 - 12:14

it can also happen, if there is a hub, and a user connect both end of hub with cisco switch. thats what happened to us few times, and currently , i am looking for a solution, any thoughts to avoid my partocular case?


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