[rbridge] Ambition with different VLAN configurations

[Radia Perlman]

Dinesh G Dutt wrote:
>
> Will it need to support both (three if you include the currently 
> dominant model, Cisco's) spanning tree protocols, IEEE STP and MSTP 
> (Cisco's PVST is IEEE's STP run per VLAN).
How different are these? How much trouble is it to listen to all the 
variants? I assumed they
were all interoperable. What happens if there is a bridged network with 
bridges that
support different of these variants?

 From what I remember of "original STP" and "RSTP", listening to them 
should be identical.
RSTP uses the same message formats, and is the same protocol other than 
adding loop prevention
messages. So I'd assume if you are listening, it wouldn't matter if it 
was STP vs RSTP.

MSTP, if I understand it correctly, involves noticing that different 
bridges are root for different
VLANs. However, maybe we can ignore that, and only listen to messages 
for the spanning
tree for VLAN 1. I'm assuming we can do that -- someone should correct 
me if I'm wrong. The
other plausible alternative is to listen to all the spanning trees, and 
if you're doing load splitting
of DRBs (one for VLANs 1-50, and the other for VLANs 51-79, say), then 
in the pseudonode
representing VLANs 1-50, you'd list the root bridges for the spanning 
tree associated with
each of the VLANs 1 through 50.


As for your description of "PVST" -- again, the implication might be 
that if you have a pseudonode
representing all the VLANs, you'd have to list, in that pseudonode, a 
different bridge ID since
(if I understand what PVST is from your one phrase above), there might 
be a different root
bridge ID for each of those.

But...I *thought* that the spanning tree is guaranteed not to be 
partitioned, so listing just the
root of the spanning tree corresponding to VLAN 1 should be all you need 
in order to detect
that there's an RBridge on the same link that you're not hearing Hellos 
from, right?

*****************
And as for allowing configuration to be some other VLAN other than 1 -- 
that makes things
complicated, because what do you do if some of the RBridges on a cloud 
are configured differently
from others?

Radia