observed huge amount of STP BPDU in Cat3550

Unanswered Question
Feb 9th, 2007

Hi, my customer network is facing some intermittent connectivity problem lately. After deploying a sniffer, there seems to be a huge amount of STP BPDU during the outage. The host connected to this switch cannot receive any packet from the router which is on the same segment. I have attached a print screen for your reference. Any advice is much appreciated. Thanks.

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Francois Tallet Fri, 02/09/2007 - 08:59

A huge amount of STP bpdus??? I see one bpdu every two seconds, which is the default hello time for STP. Basically, that's as few bpdus as can be;-)

The topology change flags are not even set in the bpdu decoded, which suggests that STP has not detected a change recently (it does not mean there cannot be an L2 issue).

If you have spotted two systems that have problem communicating together during the outage, that's already a great step in term of troubleshooting. Could you provide us with the "sho span" output for the ports on the path between these two hosts? (when the problem does not occur and, if possible, when the problem occurs). This should quickly show if STP is involved.

Regards,

Francois

vijayasankar Fri, 02/09/2007 - 09:03

Hi,

From the sniffer capture screenshot, i couldn't see any abnormal activity.

The BPDUs that are visible in the capture are normal ones.

They are just the normal configuration BPDU's where are transmitted every 2 seconds.

If we could notice any TCN BPDU's then it might indicate a potential problem happening in some part of the network.

But in the trace provided, there are not TCN BPDU's. Hence the problem that is faced in this network might not be related STP.

Have you captured any diagnostic command outputs from the Switch to augment that the issue might be related to STP.? ( show spanning-tree related commands)

Kindly provide us more details on the problem faced by the customer and any related troubleshooting done to isolate the issue.

-VJ

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