[rbridge] loops in trill networks

[Radia Perlman]

RBridges do not participate in the 802.1d spanning tree. The neither 
generate
nor forward spanning tree messages.

They look to bridges
like routers do today. If you had a big 802.1d broadcast domain, and 
partitioned
it into n pieces, with the pieces connected with RBridges (and not with 
bridges),
you'd wind up with n spanning trees that did not see each other.

Radia



Larry Kreeger (kreeger) wrote:

>This brings up another question.
>
>What does the RBridge network look like to the 802.1 bridged network.
>Does the RBridge network pretend it is a giant 802.1D bridge -
>exchanging BPDUs at its edge ports with the 802.1 bridges and blocking
>edge ports if it detects a loop?  What happens to the BPDUs sent by
>802.1 bridges to the RBridges?
>
> - Larry 
>
>-----Original Message-----
>From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
>Behalf Of Joe Touch
>Sent: Tuesday, October 11, 2005 8:26 AM
>To: Developing a hybrid router/bridge.
>Subject: Re: [rbridge] loops in trill networks
>
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>
>Loa Andersson wrote:
>  
>
>>Oh, yes it is true ...
>>
>>but I thought that a trill network could consist of a mixed of 
>>rbridges and the type of bridges that exist today, if that is the case
>>    
>>
>
>  
>
>>you can possibly form the loop over only non-rbridges
>>    
>>
>
>The conventional bridges have a spanning tree, which is what already
>prevents such loops currently.
>
>Think of the path between two nodes (hosts, routers, etc. - anything
>that sources/sinks L2 frames) as having three components (at most):
>
>node--->(bridgepath1)----(rbridgepath)----(bridgepath2)--->node
>
>the ingress (bridgepath1) and egress (bridgepath2) conventional bridge
>paths use spanning trees, so they can't have loops.
>
>The rbridge uses the TTL, so it can't have a loop at its layer. Even
>when it tunnels over conventional bridges ('inside' the rbridge, in a
>sense), those can't have loops because they're spanning-tree.
>
>The combination of spanning tree in all bridge paths and TTL in the
>rbridge logical path prevents loops in the node-node path.
>
>Joe
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