spanning tree loop

[p.holley]

Hi,

I am getting the following error on my root switch:

.Jun 16 17:12:39.168 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:0E:7F:FD:F5:BA in vlan 10 is flapping between port Gi1/1 and port Gi5/20

I have 7 switches connected in a loop, and have configured my core 4506 switch as the root for all vlans.

I have issued the "sh spanning-tree vlan <number> on all switches, and I can see that my root switch is same on all switches for all vlans.

I also issued sh spanning-tree blockedports, and I can see the ports blocking to prevent stp loop.

However, the above error indicates that I have stp loops on the network. I cannot find the loop.

Any ideas in finding it?

[p.holley]

I am just updating my question with a diagram. I am getting the error :

Jun 16 17:12:39.168 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:0E:7F:FD:F5:BA in vlan 10 is flapping between port Gi1/1 and port Gi5/20

on the Cat4506. Even after shutting down gig1/1 on cat 4506, I still get the error on gig1/2 and port gi5/20

.Jun 16 17:51:29.588 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:0E:7F:FD:F5:BA in vlan 10 is flapping between port Gi1/2 and port Gi5/20

[Kevin Dorrell]

I am not clear from your diagram where Gi5/20 fits into the picture. Also, where on the network is this host 00:0E:7F:FD:F5:BA - is it on Gi5/20?

On the loop connecting the switches, are all the links trunks? If so, is there any chance that there might be a native VLAN mismatch on any of them?

Are you running PVST+?

Kevin Dorrell

Luxembourg

[p.holley]

Correct. The host 00:0E:7F:FD:F5:BA is on port Gi5/20 on the Cat4500 switch.

All the links are dot1q trunk. I am going to check now for native vlan mismatch.

Thanks

[ankurbhasin]

HI P.Holley,

I do not think it is a STP loop as its a single mac address which is flapping.

If you see the message appearing for one or two MAC addresses, you need to locate these MAC addresses and see why this is occurring. As you have already detected one one side which is port 5/20 we need to track down the other ports also.

This link will give you a detail picture how to troubleshoot your problem.

http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a00801434de.shtml#subtopic1k

Just make sure the host connected on port 5/20 does not have 2 nics connected to other switches also or it can be a problem with broken nic also. Just check the link and you may be able to track down your problem.

HTH

Ankur

[p.holley]

Thanks Ankur,

I will have a look at the link. I did not think it was a STP loop either, especially as I disconnected the cable that completed the loop, and still was getting these errors

[ankurbhasin]

Hi P.holley,

I an kinds sure its a bad nic. Just check that again.

Regards,

Ankur