Spanning Tree Problems with Access Points connected to Procurve Switches

[simon_eng]

Anyone ever find switchports flapping on an off when Spanning Tree is active and an access point (7055, 7363, 7372, 7962) is connected? We have found this in several properties now with very similar configurations but have not been able to determine a cause. All of our hotels use Procurve switches at the edge (2910al-PoE or 2520-8G-PoE), all participate in spanning tree, but we only observe the flapping on about 1% of switchports. Of course, 1% for us means that 10-50 guests are getting knocked off the network regularly, so it is a bit of an issue (some ports have 200-300 state transitions *per day*.

We have verified that the configurations on the ports that have the problem match the ports that do not with regard to BPDU filtering, root-guard, etc. We do not believe that it is a deliberate attack because it is the same access points that have chronic issues, whereas the other 99% never do.

Any ideas?

[keith_redfield]

Hi Simon,

If you aren't doing any mesh, you can safely disable spanning tree on those (leaf-node) ports to see if that's related to the issue.

My colleagues suspect it's related to POE (overload, faulty wiring, etc). Are you getting any other error messages on the switch?

[simon_eng]

Hi Keith,
Thanks for the suggestion. I should have mentioned this in the original problem description, but we have BPDU protection, Loop Detection, and all the ports forced to Edge except for inter-switch links.

I suspect you're right that it does have something to do with the wiring, a faulty switchport, or the AP(s) are themselves faulty in some way, Unfortunately we aren't getting much in the way of error messages from any of the components apart "Help, I'm dead".

We have in the past tried switching out the patch cables and the cable runs themselves have tested out good. Moving the AP moves the problem *sometimes* but not always, and the AP diagnostics don't yield much.

Perhaps, also, the title of the issue is misleading: I included Spanning Tree in the mix because the only thing that the switch complains about is having to put the port in block mode (but not as a function of the initial 3 second listening period for BPDU because the port is being forced to be an edge).

[keith_redfield]

Is it usually a particular model AP implicated? Just for example our indoorAP failure rates are extremely low (much less than 1% typically) so it's unlikely you're seeing actual hardware failures based on the description.

[mike_mulcahy_59]

Simon,
I've experienced this exact same problem. Took down my entire network one night. No idea what caused it. The port the AP was connected to started flapping, then go blocked, but the AP would Mesh to other APs and continue to flood the network. Eventually all of the uplink ports ended getting blocked, and the only way to get around it was turn off STP, disable Mesh on the APs, then we were able to turn STP back on.....definitely not a fun night. We have 7363, 7982, 7762, and 7962s