[c-nsp] backup with STP

[lists at hojmark.org]

> Agreed in a network running PVST+ it would've been far simpler
> to transition to RPVST+, and harder to transition to MSTP/RSTP.

Well, it's not *that* hard if you have a structured design and
know what you're doing. Start by converting the center of the STP
and then work your way out to the edge, and you should be fine.
Doing it the other way round can be a bit tricky, however.
 
-A