[nsp] VLAN database propagation

[sthaug at nethelp.no]

> > We run all switches in VTP transparent mode, and use "allowed vlan"
> > on all trunks. This has dramatically reduced our VLAN problems.
> 
> same results could have been reached using vtp with pruning. 

A couple of issues here:

- VTP with pruning assumes that VTP masters are "well behaved". We have
had several cases where this definitely was not the case.

- "allowed vlan" gives you much more explicit control than VTP pruning.

In the end it all comes down to the fact that using VTP (and pruning)
allows *one* switch (the VTP master) to create major f***ups in your
network. Using transparent, the switches are independent. This works
much better for us. YMMV.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no