[c-nsp] Divide large PVST domain?

[Victor Sudakov]

John Gaffney wrote:
> You could consider MST to reduce the number of STP instances.
> Sometimes that can increase efficiency. 

Am I correct to assume that every time I need to move a vlan from one
MST instance to another, my whole MST domain will fall apart until the
MST reconfiguration is complete on all the switches?

Somehow I don't like this idea.


> However what you are probably looking for is "spanning-tree
> diameter" command. If I recall that can make some auto adjustments
> to STP timers to accommodate for large switched networks.

Even with the timer adjustments the maximum diameter is about 18
devices. Still my train does miraculously work provided the root
switch is in the middle.


> You should also be aware that 20 switches connected in a straight
> line (hence middle switch) gives you a single point of failure. 

It is not exactly so because the radio equipment has a way to shunt
the failed switch. So the continuity of the train can be quickly
restored. But it is a different topic.

I also have a backup root close to the middle of the train.

This is also the reason why going all L3 is not an option. You cannot
simply shunt a router.

> If it is truly a "train" of switches you could also not run STP - no
> ring/redundant link = no loop. 

As I have already said before, 'I have a "train" topology with some
redundant links between neighboring switches'. 

There are however no rings in the sense that redundant links are only
between neighbors.


-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru