I have the BCMSN course manual, which I think is what Karen Webb's book is
directly based on. That's pretty much my sole basis for the following blurb, so
it may not add anything to your understanding. I'm no guru on spanning tree, so
hopefully somebody else will correct me if I'm wrong.
Basically, PVST is Per VLAN Spanning Tree - one spanning tree for each VLAN. I
tend to think of this as a little bit like 'ships in the night' routing - each
VLAN works out its own spanning tree, and doesn't have to worry about any of the
other VLANs. Don't take the analogy too far, though, as I certainly am not
trying to say that spanning tree is equivalent to routing.
There's more overhead on the network, as there are BPDUs for each network and
the switches have to work out a spanning tree for each VLAN, but you can
optimise the network more effectively. For example, you can send traffic for
one VLAN down one path and traffic for another VLAN down another path, which
helps with load sharing.
PVST is Cisco proprietory, and needs ISL to work.
CST is Common Spanning Tree - IEEE 802.1Q. This creates a single spanning tree
that is used by all VLANs. Less overhead (only one spanning tree to process),
but it can mean that some VLANs don't have very efficient paths, as the spanning
tree will be a compromise. VLAN1 is used to run the spanning tree protocol.
PVST+ is Cisco's extended version of PVST, used for compatability with 802.1Q
CST. I got the impression with the course manual that the information on PVST+
was pulled pretty much straight from the advertising blurb with no real
explanation. Or maybe I'm just not taking it in very well either. I could copy
what it says but it's no doubt in the Webb book so I won't repeat it. I think
it's basically PVST with bells and whistles so it will run with 802.1Q
If you have any specific questions or bits you don't understand, fire away and
I'll take a stab.
JMcL
-- Forwarded by Jenny Mcleod/NSO/CSDA on 18/07/2000 16:48
---
jeongwoo park <[EMAIL PROTECTED]> on 09/07/2000 11:07:05
Please respond to jeongwoo park <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
cc:(bcc: JENNY MCLEOD/NSO/CSDA)
Subject: Qs on PVST, CST, and PVST+
Hi all
I am in the middle of studying for BCMSN test.
I read these concepts many times from the Karen Webb's book trying to
understand.(Page 147-150)
Unfortunately, it wasn't still clear for me to tell the difference and
understand their adv and disadvantages.
Can anybody clarify these concepts or give me any links that help me
understand?
Thanks in adv..
iWon.com http://www.iwon.com why wouldn't you?
...
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