Subject: [rbridge] seekinginputon abstractfor problemand applicabilitystatement

From: sanjays at cisco.com (Sanjay Sane (sanjays))
Date: Fri, 14 Oct 2005 11:49:16 -0700

If rbridges blocked BPDUs, you may lose the root-id and root-cost
information of the spanning tree. Thus, the points at which the rbridge
spanning tree hooks up to L2 spanning tree may not be optimal. i.e.
Consider rbridge cloud having many intersections with external spanning
tree cloud. The choice about boundary ports (designated rbridges) may
have to be made entirely based on rbridge's view of the topology. 

Whereas, if rbridges participated, and  
-- created their own internal spanning tree
-- propogate the external L2 spanning tree BPDU over its internal
spanning tree, thus retaining the root-information to make good choices
about boundary ports. 
-- participate with external L2 spanning tree only at the "boundary
ports"
-- turn the rbridge cloud into a single virtual bridge. 

(this would look similar to how MSTP region (802.1s) interacts with CIST
at boundary ports) 

Thanks,
Sanjay

>-----Original Message-----
>From: rbridge-bounces at postel.org 
>[mailto:rbridge-bounces at postel.org] On Behalf Of Peter Ashwood-Smith
>Sent: Friday, October 14, 2005 11:18 AM
>To: Developing a hybrid router/bridge.
>Subject: Re: [rbridge] seekinginputon abstractfor problemand 
>applicabilitystatement
>
>
>>> I think I missed something, what breaks if we block BPDUs ?
>
>>If nothing, then lets. For bridges too.
>> Now what happens? (i.e., if bridges block BPDUs) - won't 
>that kill the
>spanning tree?
>
> Yes of course if you block a BPDU the bridge will stop the 
>STP tree at that point. Thats exactly what we are trying to 
>do. Stop the STP computed portion of the FULL tree at that point. 
>  
> With BLOCK. Each protocol computes its own smaller part of 
>the bigger spanning tree.
> STP computes using BPDUS etc. and Rbridge computes using 
>IS-IS/Krusal's.
>
> When done you have a bunch of unconnected spanning trees 
>which are made into one big tree by the designated rbridge 
>concept i.e. single link.
>
> To convince yourself that this really works. Draw an 
>arbitrary tree on a piece of paper. Then draw another disjoint 
>tree somewhere else on the paper. You can make one big tree by 
>connecting any two of the points between the two trees and you 
>cannot create a loop with single link.
>That is why BLOCK works.
>
> Peter
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