mac-address flapping

Unanswered Question
May 14th, 2008

Hi All,

what are the possible causes of Mac-Address Flapping?

i have recived messages in my switch for the mac-address flapping ( Mac-Address 0201.0000.0000)

Thanks & Regards,


I have this problem too.
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Edison Ortiz Wed, 05/14/2008 - 15:22

The switch is learning the same MAC address via 2 different switchports.



Pravin Phadte Thu, 05/15/2008 - 01:32

can you provide with the error msg log,

if possible also the config on the switch. show tech-supp if possible.

shelgaonkar Thu, 05/15/2008 - 01:34

Check the OS of the machine which is connected to that port,from which the specfic mac address is identified.If it is a server OS,then disable the Network load balancing (NLB) service.

Let me know if my solution helps you.

S. Hasan Thu, 05/15/2008 - 01:40

yes this port is connected with win 2000 server with load balancing option.

how can i fix it widout disabling this load balanicg option at switch end.


shelgaonkar Thu, 05/15/2008 - 01:54

Load balancing is happening on server not switch.Remove the NLB service from TCP/IP configuration of the server

S. Hasan Thu, 05/15/2008 - 01:59

This is the requiremnt of the system. now i want to fix flapping message error without disabling the load balancing service.

Danilo Dy Thu, 05/15/2008 - 01:38


Do you use etherchannel? Check your etherchannel configuration between switches.



Edison Ortiz Thu, 05/15/2008 - 04:50

If you have 'load balancing' configured at the server, you must also configure 'load balancing' at the switch, otherwise it won't work.

At the switch side, configure the following on the ports where this server is connected.

interface fx/x

channel-group x mode on

Note, replace the x in the channel-group with the port-channel number you want to use for this implementation. You also need to do this command on both ports at the same time if possible. Do this procedure during a maintenace window




S. Hasan Fri, 05/16/2008 - 00:45

NIC's of this server are conected with two diffreent switches.and both switches could not communicate with each other.

can you please assist me that how can i configure load balancing.

or is there any other solution if any

thanx - raheel

Edison Ortiz Fri, 05/16/2008 - 04:58

this server are conected with two diffreent switches

Well, that changes the whole design suggestion. It can't be done. Please disable the load-balancing in the server to avoid the mac-address flapping in your switch network.

I'm not a server guy but I believe you can enable some kind of load-balancing in the server without sending the same MAC address to the switch. I believe the option is fault-tolerance or load-sharing.





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