[c-nsp] pvst and mst

[Andrew Metcalf]

I am running a mix of MST and PVST on one network without problems (+40
switches). The roots for both protocols should be setup to be the same
switch, that's probably the most important thing I've noticed so far.
However, I might revert back to rapid pvst because I miss the flexibilty
having a one-to-one spanning tree to Vlan mapping built in. I do have a bug
where the 2950s I have stop responding to management traffic if there is a
mis-match between the number of VLANs that it is running and the number that
is on it's trunked uplinks, but I can't remember if that is MST related, I'd
have to dig the bug ID up. VTP or strict change control "fixes" that anyway.
I have the possibilty of having to use many many VLANs in the future, which
is why I decided to go with MST for now.

As for migrating, I don't know of a really slick way because I did it as I
was migrating OS revs anyway, but once you migrate one switch as the root
(like I said the same as the PVST root switch preferably), you should be
able to migrate the rest of the switches one at a time. MST is very quick,
so you're only talking about a few seconds of outage. My root switch
accomidates the existing PVST switches with no problem, but making the
change on that root switch should be the biggest headache.

Anyone have advice for adding a new MST Instance on a production network
sanely?

Andrew

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Alexander Koch
Sent: Thursday, March 17, 2005 8:17 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] pvst and mst

Hello folks,

hopefully someone can clue me in that knows the whole story.

We have a mixture of 3508 and 2950 Cisco switches in some sports of our
network and the number of VLANs increased a lot lately. Now, the 3508 cannot
do MST or rapid-pvst if I am not mistaken. That being said I have basically
two Q's:

1. Can psvt and mst co- exist? I get told they can, it has to do with
setting all ports (default) to portfast except the trunks, and then mst and
pvst can live fine with each other. Obviously we need that thing to work
with the 3508.

2. Is there a sane way to switch from pvst to mst, without losing management
completely? ,-) It probably is related to the 1st question, yes, but how
does one migrate from a to b here the easiest way?

Any clues/ideas/hints would be highly appreciated. I have heard n+2 stories
from n ppl so I wanted to better double- check here.

Thanks lots,
Alexander

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