Spanning Tree Protocol 802.1D vs. 802.1w

mike15400 · ‎02-17-2009

Is there is difference in the initial STP convergence process when using 802.1W rather than 802.1D?

I find many descriptions about convergence after a topology change but nothing on 802.1W initial convergence.

I am te4aching a BCMSN class...

Tshi M · ‎02-17-2009

This link might have what you are looking for:

http://www.cisco.com/application/pdf/en/us/guest/tech/tk621/c1501/ccmigration_09186a0080174993.pdf

Giuseppe Larosa · ‎02-17-2009

Hello Mike,

the initial phase is quite similar with the root bridge election.

I agree that the real differences start later.

The only doubt would be the presence of some form of flash updates that could shorten the convergence time.

One first basic difference is that the BPDU with 802.1W becomes a keepalive mechanism so if a switch doesn't receive the bpdu on its root port still sends out the bpdu out its designated ports.

After three missing BPDU a blocked port starts to move to forwarding.

For this similarity probably little focus is given to the initial startup of the protocol.

Once the topology is established a change can be managed with the BPDU handshake, synchronization process.

Hope to help

Giuseppe