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New Member

Flapping in Log

In the log on a 4912 I am geting a message about flapping. Can someone tell me what flapping is and what's causing it?

7 REPLIES
Cisco Employee

Re: Flapping in Log

could you post the exact message.

New Member

Re: Flapping in Log

Here is the exact error message in the log:

2002 Mar 07 06:28:40 CST -06:00 %SYS-4-P2_WARN: 1/Host 00:40:96:37:70:fa is flap

ping between port 2/1 2/2 and port 2/6

Thanks

Purple

Re: Flapping in Log

This is telling you it is seeing this mac address on all these ports , possible loop or something . I would look and see what is attached to these ports that might cause this .

New Member

Re: Flapping in Log

Do you have wireless access points on the switch in question? A wireless user switching back and forth between two access points on different ports will appear to the switch to be flapping. The only "solution" is to plug all your access points into a hub and plug that into the switch, which will mask the flapping from the switch. Or just ignore the messages.

New Member

Re: Flapping in Log

Hi,

This could be due to spanning tree or physical layer problems. Please refer to the troubleshooting steps outlined in this document:

http://www.cisco.com/warp/public/473/62.shtml#casestudy4

Nash

New Member

Re: Flapping in Log

"Flapping" means the switch is seeing the mac address (nic card hardware address) appearing on different switch ports. If the address changes ports a lot, the switch tells you about it. The switch cares because it has to keep a table of which mac is on which port, so it knows where to send packets. The switch is grumbling about having to update its tables a lot.

New Member

Re: Flapping in Log

One thing that does'nt seem to be metioned is etherchannelling.

Maybe the host has etherchannelling enabled and the switch has'nt.

Barry.

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