%C4K_EBM-4-HOSTFLAPPING:

Unanswered Question
Oct 10th, 2007

Hi NetPro,

i got this syslog msg,

Oct 10 17:52:24.484: %C4K_EBM-4-HOSTFLAPPING: Host 00:02:8A:AA:45:1A in vlan 296 is flapping between port Fa2/3 and port Gi1/2

and this is my switch port configuration. is this correct config ?

switchport trunk encapsulation dot1q

switchport trunk native vlan 296

switchport trunk allowed vlan 296,312,314

switchport mode trunk

kindly correct me if you feel i am wrong, and your reply will be highly appreciated.

regards,

Jackal

I have this problem too.
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Kevin Dorrell Wed, 10/10/2007 - 17:53

This means that the switch is seeing the same MAC address from two different directions in rapid succession, and is confused about where to send its packets. Ususally due to a looping problem.

Is that config on both those ports? It looks fine to me. Is the native VLAN the same at both ends of the trunk, i.e. on the connecting switch?

Kevin Dorrell

Luxembourg

ney25 Wed, 10/10/2007 - 17:57

Hi Kevin,

thanks for your prompt reply, if it is looping problem then how do i find out the looping problem ?

thanks.

Kevin Dorrell Wed, 10/10/2007 - 18:02

Can you draw out a topology diagram for VLAN 296? Which port is that MAC address actually connected to?

Please also check that your native VLAN is the same at both ends of each trunk link. What is this port connected to? Can we see the config at the other end of that link, and also on both ports implicated in the flapping?

Kevin Dorrell

Luxembourg

ney25 Wed, 10/10/2007 - 18:06

Hi Kevin,

thanks for reply, ok . basically vlan 296 is my Wireless vlan, and from the switchport config . native vlan 296 is actually connected to my AP.

switchport trunk encapsulation dot1q

switchport trunk native vlan 296

switchport trunk allowed vlan 296,312,314

switchport mode trunk

thanks

regards,

jackal

Kevin Dorrell Wed, 10/10/2007 - 18:16

Is there only the one AP on this VLAN, or several? I don't have much experience in wireless, but I think that may be an essential part of your problem. I had better hand over to someone with more experience in that field. Sorry.

Kevin Dorrell

Luxembourg

ney25 Wed, 10/10/2007 - 18:24

Hi Kevin,

thanks for your prompt reply and info. i appreciate.

thanks a lot.

regards,

Jackal

JBUIST Thu, 10/11/2007 - 07:45

Can you verify that the user is not plugged into both the wireless and the lan. This will cause the hostflap that you are seeing.

lgijssel Thu, 10/11/2007 - 08:28

You will have to troubleshoot this yourself, we can only give you some hints.

Back to message you receive:

Oct 10 17:52:24.484: %C4K_EBM-4-HOSTFLAPPING: Host 00:02:8A:AA:45:1A in vlan 296 is flapping between port Fa2/3 and port Gi1/2

fa2/3: is this the interface that is physically connected to the AP?

Gi1/2 is on the supervisor module. This is almost always the backbone link to the second switch in a redundant configuration.

Do you see the same messages on the other 4500 as well?

You will also need to find out to which host the mac address belongs. It could be the AP itself, a wireless client or something else.

Finding the originating host is a key to discovering the loop.

Feel free to post additional questions after doing some troubleshooting!

regards,

Leo

ney25 Thu, 10/11/2007 - 16:27

Hi Leo,

yes, Fa2/3 is connected to the AP.

and u are right again, the error msg appeared on another cat 4500 as well.

ok , i will get back to you again.

thanks for the update.

regards,

jackal

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