[c-nsp] Maximum spannig tree instances

[Ross Vandegrift]

On Thu, Jul 16, 2009 at 08:51:47AM +0200, Gert Doering wrote:
> On Wed, Jul 15, 2009 at 11:27:12PM -0400, Ross Vandegrift wrote:
> > On Tue, Jul 14, 2009 at 05:00:36PM +0200, Gert Doering wrote:
> > > <rant>
> > > MST is what comes out if vendor committees get together, and agree to
> > > implement the least common determinator in the most complicated way.
> > > </rant>
> > 
> > I completely disagree - it's what comes out of solving problems
> > related to the LAN - the LOCAL area network.  In virtualized LANs,
> > there's typically only a few possible physical topologies that can
> > exist.  MST seeks to exploit this to lower the amount of processing
> > power that is required.
> 
> Since MST was standardized long before the "virtualized LAN" environments
> were common, this is a nice after-the-fact explanation - but the fact
> that *years after protocol design*, networks have emerged that make MST
> actually work doesn't make it a better protocol.

I think you've misunderstood me - by "virtualized LAN" I meant VLAN,
not VPLS.  It didn't take years for these designs to come up - the
datacenter we run is a bog-standard, utterly uninteresting case of a few
thousand servers, in a few thousands VLANs, with a pair of HSRP
routers.

The point of MST is to realize that there's never going to be more
than two possible forwarding topologies, and computing more is a total
waste.  It's a perfectly fine protocol at acheiving that goal.  I
realize you might not care about that goal, and that's okay.

I'll go a step further - I doubt that there's a substantially more
optimal way to compute only the valid topologies.

-- 
Ross Vandegrift
ross at kallisti.us

"If the fight gets hot, the songs get hotter.  If the going gets tough,
the songs get tougher."
	--Woody Guthrie