spanning tree

Unanswered Question
Oct 25th, 2007

Hi all, can anyone tell me when running spanning tree in my network, if I disable spanning tree on the single uplinks to my switches from the distribution switch will the switches not receive any bpdu's ? but yet on all the access ports on my access switches if i still have spanning tree enabled will they still work ?

I have this problem too.
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bvsnarayana03 Thu, 10/25/2007 - 06:17

Disabling spanning tree on the uplink may lead to network outage in case of active switch or uplink fails. Spanning tree helps calculate alternate path & block it when primary path is unavailable.

Also, since access ports only have hosts connected & no n/w devices, its advisable to run portfast on these ports to eliminate the delay in change of port state from listening to forwarding.

Francois Tallet Thu, 10/25/2007 - 09:16

From the emails you have posted recently, I think I understand that you have several access switches connected non redundantly to some distribution switches and you want to filter out the TCN they might send.

The cleanest solution to do that is to configure portfast on all the edge ports of the access switches. This way, they would not generate TCN in the first place.

We don't have a feature that filters only TCN and keep config BPDUs at the same time. So our only option here would indeed be a combination of portfast and bpdufilter if you wanted to disable STP on the downlink (or uplinks of the access switches). I would not suggest doing so for "safety" reasons, but that's possible.



carl_townshend Fri, 10/26/2007 - 00:15

thanks for that

however, if I did disable spanning tree on the uplinks, would this stop my access switches receicving bpdu's from the root ?

Francois Tallet Fri, 10/26/2007 - 06:18

Yes, that's why I would not recommend it. Not that it would be an immediate problem considering that you don't have redundancy. It's just that you are losing the safety net of having spanning tree detecting a loop that could be added as a result of a bad cabling for instance.

Topology changes are not that bad, and they can be prevented by portfast. We even have a global "spanning-tree portfast default" command that you can enable on your access switch to enable portfast in one shot on all the access ports. That will have the effect you are looking for, without removing STP.




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