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New Member

PVST+ question


I have a question regarding PVST+.

There are two building close to each other. They are connected via a wireless 11Mbps microwave and a 100Mbps wireless laser connection. The 11Mbps connection is the backup link. In each building there is a Catalyst 3550 switch. There is no routing between the LANs they are bridged. Two VLANs exist (voice and data). I tried to use load balancing between the links(I used STP port priority). I assigned one of the switches to root bridge. The data VLAN used the 100Mbps and a voice used the 11Mbps microwave link. It worked(I checked the blocking ports in each VLAN) but occasionally topology changes occured (it was traffic dependent, e.g. at night there was no any topology changes) thereby a loop emerged. I checked on it and I found that the microwave devices (debian linux with a Lucent wireless LAN card) sent BDPUs. I disabled the STP on the debian linux but it caused bigger problem because it didn't forward the BDPUs of the Cisco Catalyst 3550. When I planned the STP topology I didn't count the BDPUs of the debian linux.

My question is: Is it possible to use PVST+ if an intermediate device doesn't support PVST+?

Is there any solution to use load balancing between the two links and provide redundancy?

Thanks is andvance


New Member

Re: PVST+ question

Yes, this is possible.

1. When you connect a Cisco switch to a non-Cisco device through an 802.1Q trunk, the Cisco switch uses per-VLAN spanning tree+ (PVST+) to provide STP interoperability. It combines the spanning-tree instance of the 802.1Q VLAN of the trunk with the spanning-tree instance of the non-Cisco 802.1Q switch.

New Member

Re: PVST+ question

To answer your first question, it is possible, Please the following document

To answer the second question, refer to the following

Hope this helps

New Member

Re: PVST+ question

Thanks for your answers.

I've solved our problems

Lajos Csemy