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Webcast-Catalyst9k
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RSTP BPDU debug/logging

Hi guys,

We have recently upgraded parts of our network, as well as upgrading from PVST to RPVST.

Problems have come along where the wireless links between the switches do not cope with topology changes, but this is a whole other problem.

The actual problem comes from linking between two switches with two wireless links.

Logging on the remote switch shows RSTP moving to the second link due to lack of root BPDUs on the primary radio circuit. Yet 2-3 seconds later it shifts back to the primary link. In doing this it is causing problems further on down the network.

During some of my reading of STP I found a page explaining all the timer details as well as an option to do debugging on BPDU packet timings. All I remember was that it was an option which would log timing faults on BPDU packets.

Other than finding this command, are there any other options for BPDU debugging/logging to find out why its selecting the secondary.

056650: Mar 23 22:22:39: RSTP(10): updt roles, root port Fa0/16 is going down

056651: Mar 23 22:22:39: RSTP(10): Fa0/17 is now root port

Now using pings to the remote switch shows no problems the entire time, we are using default timers, which should mean that traffic should stop to the remote site for at least 6 seconds.

Any & all help is appreciated, and pre thanks to Francois

Regards Richard

1 REPLY

Re: RSTP BPDU debug/logging

Hi Richard,

From you debug, it seems that the port is physically declared down to the spanning tree, it's not that the message age expires but rather that your uplink is flapping:-( You can probably confirm this by configuring "logging event link-status" on the interface.

Ping is not affected because RSTP recovers instantly this failure. Downstream bridges must experience some syncs as a result of this flapping, which must explain the connectivity instability further down the network.

Regards,

Francois

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