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Host Flapping Between Port Channels

Unanswered Question
Oct 2nd, 2008
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I get the following error message.

Oct 2 DATA % C4K-EBM-4-HOST FLAPPING: HOST MACADDRESS in vlan 8 is flapping between port PO3 and port PO15. Sh mac-address-table address MACADDRESS continues to show me the PO3 or PO15 as the interface location. How do I find this host and stop the flapping? Catalyst 4000 12.2(25).



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valglinskiy Thu, 10/02/2008 - 09:08
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You might be having spanning-tree loop. Make sure that you have STP enabled on the switch. You can also disable either PO3 or PO15.

It could also be that you have 2 servers running redundant service which flaps between 2 hosts frequently. Based on MAC address in error message you can find out manufacture of network card (or service) and make educated guess. Of cause, the easiest way is to manually track the network cable from the switch port to host.

new_networker Thu, 10/02/2008 - 09:51
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Check if the servers have the NIC's configured in an etherchannel. Seems like dual NIC's on your server is terminating on two different switches and Cisco switches do not support etherchannel with single host across multiple switches.

Try configuring the NIC's on the server as active/passive.

satyamothukuri Thu, 10/02/2008 - 21:56
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Check ur uplink switches 1 by 1.start from the last switch which is having no child.


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