[c-nsp] pvst and mst

[Matt Buford]

Although this works for a migration, I wouldn't recommend this as a 
long-term solution.

A big catch is that when a non-edge port changes state, spanning tree on all 
ports on the same VLAN (or all VLANs if trunked) on the same switch are 
reset.  For your RPVST neighbors, reconvergence is quick and it is no big 
deal.  For your PVST neighbors, you get a nice big outage.

We had a 6500 with trunked RPVST backbone links, a number of servers, and a 
PVST link down to a couple old legacy 3500XL's that can not speak RPVST. 
Every time someone rebooted one of the servers, the link to our old PVST 
switches would reset spanning tree, giving us a nice 30-45 second outage. 
Setting all server ports to portfast/edge avoids the issue for the server 
ports, however if one of our RPVST backbone links flaps the PVST ports still 
take a hit.

According to Cisco, this is not a bug, but is the normal behavior.

----- Original Message ----- 
From: "David J. Hughes" <bambi at hughes.com.au>
To: "Alexander Koch" <efraim at clues.de>
Cc: <cisco-nsp at puck.nether.net>
Sent: Thursday, March 17, 2005 8:24 AM
Subject: Re: [c-nsp] pvst and mst


>
> From our experience, dodge MST.  Rapid PVST can happily co-exist with
> "standard" PVST so your legacy Cisco switches will be well supported.
> Migration from PVST to RPVST is a much more pleasant experience (and a
> lot easier to revert if it all goes pear shaped).
>
>
> David
> ...
>
>
> On 17/03/2005, at 11:16 PM, Alexander Koch wrote:
>
>> 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?
>
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