[rbridge] Ambition with different VLAN configurations

[Dinesh G Dutt]

Hi Radia,

Radia Perlman wrote:
> 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?
Don't know how different things are. MSTP/RSTP can interoperate with 
older STP, I believe.
>
> 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.
The PDUs look different between MSTP and regular STP.
>
> 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?
I think you maybe right here.
>
> *****************
> 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?
I agree. I prefer to not provide a configurable option on this, but I 
can foresee people complain,

Dinesh

-- 
We make our world significant by the courage of our questions and by 
the depth of our answers.                               - Carl Sagan