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New Member

host Flapping at 4506 switch

I am facing typical problem.Everyday in the morning at 9:05 AM I get host flapping messages on 4506 switch and machines looses the connectivity and rest of the day no flapping.I have checked up there is no spanning tree loop.

My question is if spanning tree loop is there then flapping should happen full day but it happens for 1-2 mins everyday morning.

Can anybody help me ?

thanks

13 REPLIES
Silver

Re: host Flapping at 4506 switch

This might not be a problem with the switch as such. It is most probably a problem originated with the devices attached to these ports. Here's a link on spanning tree protocol troubleshooting.

http://www.cisco.com/warp/public/473/16.html

What is the exact message that you are receiving? Use the Error message decoder to interpret the message.

New Member

Re: host Flapping at 4506 switch

You may want to check out where these hosts ends up during the day. And, in the morning, figure out why it is being seen on the other port. You'll need to know the L2 path and trace it backwards.

By the way, it is normal for the switch to not forward packets to the MAC reporting the flapping. Please see below for further T/S details.

http://www.cisco.com/warp/customer/473/176.html#subtopic1k

New Member

Re: host Flapping at 4506 switch

These machines are servers so there location is permanent.

New Member

Re: host Flapping at 4506 switch

How is it possible if it has a single connection to a switchport. Possible that these servers have dual-port NICs who share the same virtual MAC?

New Member

Re: host Flapping at 4506 switch

That is what surprising me too...I have double checked that no server has dual NIC cards and servers are having single connection only

New Member

Re: host Flapping at 4506 switch

You have to check if these servers are connected to another switch and possible loop in the morning. Or, could be that other servers somehow are using the same MAC when initially brought up and then use something else. Since it happens everyday at the same time, sniff those 2 ports and see what is going on.

New Member

Re: host Flapping at 4506 switch

You have to check if these servers are connected to another switch and possible loop in the morning. Or, could be that other servers somehow are using the same MAC when initially brought up and then use something else. Since it happens everyday at the same time, sniff those 2 ports and see what is going on.

New Member

Re: host Flapping at 4506 switch

One more thing on some servers more then one IP address has been configured,

New Member

Re: host Flapping at 4506 switch

You have to check if these servers are connected to another switch and possible loop in the morning. Or, could be that other servers somehow are using the same MAC when initially brought up and then use something else. Since it happens everyday at the same time, sniff those 2 ports and see what is going on.

New Member

Re: host Flapping at 4506 switch

I've had this problem once before also.. from what I can remember there was a old server that someone decided to turn back on, this old server was running some software that used a software defineable MAC. That software defined MAC was a duplicate of another MAC now on the network (specificly on the same switch). We just found the old server made sure it stayed off, and this fixed the problem for me.

New Member

Re: host Flapping at 4506 switch

How to find out which machine is configured with this type of software ?

New Member

Re: host Flapping at 4506 switch

below are the messages I was getting on the 4006. I don't recall what software was running on the old server we found though. If you are getting similar messages, just track down what devices are pulugged into the two switchports in the error message. If there is another hub or switch plugged in to one of those ports, then you will have to track down every device on that hub/switch also...

2001 Aug 30 20:01:44 %SYS-4-P2_WARN: 1/Host 02:00:4c:00:00:94 is flapping between port 2/13 and port 2/10

2001 Aug 30 20:02:40 %SYS-4-P2_WARN: 1/Host 02:00:4c:00:00:94 is flapping between port 2/13 and port 2/10

2001 Aug 30 20:03:38 %SYS-4-P2_WARN: 1/Host 02:00:4c:00:00:94 is flapping between port 2/13 and port 2/10

2001 Aug 30 20:04:41 %SYS-4-P2_WARN: 1/Host 02:00:4c:00:00:94 is flapping between port 2/13 and port 2/10

New Member

Re: host Flapping at 4506 switch

I found the problem, there was misconfigured Uplinkfast and portfast command.. which was creating temproray loops .I removed these commmands...flapping is stopped...

Thanks to u all .

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