On 11/28/2012 09:13 AM, Saku Ytti wrote:
On (2012-11-28 09:55 +0100), Gert Doering wrote:
I'm sure there are topologies in which mst is suitable
Textbook topologies, obviously :-) - where you sit down, design your
network, implement it, *and then go elsewhere* instead of modifying
your network on-the-fly.
We've ran MST as long as it's been in IOS. Mostly in metrorings. We have 4
instances, for not particular reason but somewhat even VLAN divisors. But
they all have always been using same topology. And we never touch the MST
config, nor have ever had the need to do it.
We could do some micro-optimization to make sure that metroVLAN which is
terminated to eastPE has eastPE as root and meteroVLAN which is terminated
to westPE has westPE as root. And we could then define 1-2000 are westPE
terminated VLANs and 2001-4000 are eastPE terminated VLANs. But we're not
even doing this, if we'd want to do it, we wouldn't need to touch MST
config.
I know I don't see eye-to-eye to this with Gert, but I think MST is
perfectly usable in most networks if you design the network and you have
system to allocate VLANs.
Quite few networks actually need unique topology per VLAN without it being
hard-to-observe micro-optimization. But there certainly are some how can
capitalize on it.
I certainly don't *need* per-vlan topology. But I can use it at no
observable cost.
On the other hand, I could have re-numbered every vlan on every switch
at all of our sites, spent days or weeks planning vlan numbering to
ensure there were enough tags allocated to each space/zone/thing, mapped
the 15 instances IOS uses to the >45 definable topological areas, and
then watched it all break weeks later as the first "special job" came
along and I had to incur a topology change network-wide.
So, for us, MST is pointless.
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