[c-nsp] Deploying MSTP

[Matt Buford]

On Wed, Dec 28, 2011 at 5:26 AM, Frédéric Loui <frederic.loui at renater.fr>wrote:

> If you have a complex L2 topology and lots of VLAN per instance. VLANs per
> MST instance can become tedious. Might be worth to use some
> configuration/check scripts so as to make sure that all VLANs are bound to
> the right MST instance
>

Also worth noting, this hassle of needing to pre-map VLANs can go away in
an active/active Nexus vPC or Catalyst VSS environment.  Your paths are all
active/active even for a single MST instance, so you don't need to use two
MST instances to send some VLANs on the A path and some on the B path.  So,
I premap all VLANs like so:

spanning-tree mst configuration
  instance 1 vlan 1-4094

And I'm done.  I don't pre-create VLANs.  Creating a VLAN doesn't cause a
hit.  It is changing the mapping above that causes the hit.  Since I'm not
trying to spread VLANs out across 2 instances to balance traffic, I don't
ever need to change the mapping (hopefully).

But I do agree with the poster who mentioned that the CST root MUST be on
the MST side.  That one has bitten me before when trying to bridge a VLAN
between the "old" PVST network and the "new" Nexus MST network for
migration purposes.