[c-nsp] MST spanning-tree

[Ross Vandegrift]

On Thu, Jul 23, 2009 at 01:34:01PM -0400, Steven Fischer wrote:
> It seems that we can create VLANs with no issue, and by default, those VLANs
> are placed in the default instance, instance 0.  This really isn't a
> problem, but when we move the VLAN into its proper instance, a spanning-tree
> recalc appears to occur, the duration of which is long enough to interrupt
> data transfers that may be going on at the time.  Other than returning to
> PVST/PVST+, is there a way to avoid this recalc taking out half the VLANs in
> the data center for 30 seconds when adding it to the proper instance?  Will
> our planned migration to VSS mitigate this to any degree, and if so, how
> much?

You need to pre-configure your VLAN mappings so that when you add a
VLAN to a switch, it's already mapped to the instance it's going to
end up in.  For MST to work the way you want it, the mapping has to
match on every device in the extended LAN.  (right now, you might as
well be running RSTP, since each switch has probably formed its own
region).

Once you get the full map rolled out to all of the switches (make sure
you load it via TFTP - pasting it in is a bear, assuming you're
configuring all 4094 VLANs), the switches will form one region with
two active forwarding topologies.

Ross

-- 
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