[rbridge] FW: Time to summarize "forward or block" BPDU thread

[Larry Kreeger (kreeger)]

Radia,

In Step 6, is the frame sent onto the link between RB1 and B1 once or 3
times?  If once, what is the Ethernet DA? 

Thanks, Larry

-----Original Message-----
From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
Behalf Of Radia Perlman
Sent: Wednesday, October 19, 2005 3:57 PM
To: Developing a hybrid router/bridge.
Subject: Re: [rbridge] FW: Time to summarize "forward or block" BPDU
thread

Step 1: The bridges create a single broadcast domain, as seen by the
RBridges. So the RBridges see the following picture:

  B    C    D    E
  |    |    |    |
 RB1  RB2  RB3  RB4
  |    |    |    |
 ---------------------
                 |
                 A

Step 2: RB1 is elected DR, so it is the only one that will encapsulate
or decapsulate to/from that link.

Step 3: A transmits a broadcast or multicast packet

Step 4: RB1 receives it (RB2, RB3, and RB4 all throw it away since they
are not allowed to process native (non-encapsulated) packets

Step 5: RB1 encapsulates it to be sent over spanning tree "ingress RB1"

Step 6: RB1 forwards the encapsulated packet onto the link, with an
outer header with a multicast address "all RBridges"

Step 7: RB2, RB3, and RB4 all receive the packet, and decapsulate it in
order to send to their upward link (to C, D, and E, respectively).

Step 8: (which could certainly happen after 5 or 6...doesn't have to be
in order). RB1 decapsulates the packet and sends it to B.

************
Hope that helps...

Radia




Larry Kreeger (kreeger) wrote On 10/19/05 15:25,:
> Radia,
> 
> I think I now understand now that the DR election happens only between

> RBridges on a single shared link - and does not require usage of any 
> RBridge topology information.  It would help clarify the data flow for

> me (and hopefully others) if, given the network diagram below, you 
> could please give a step by step description of how a broadcast frame 
> sent by host A gets through each Bridge and RBridge in this network in

> order to be received by hosts B,C,D,E if we assume that RB1 is the 
> Designated RBridge on the "link" created by the Bridged network formed

> by Bridges B1,B2,B3,B4.
> 
>   B    C    D    E
>   |    |    |    |
>  RB1  RB2  RB3  RB4
>   |    |    |    |
>   B1---B2---B3---B4
>                  |
>                  A
> 
> Thanks, Larry
> 
> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] 
> On Behalf Of Radia Perlman
> Sent: Wednesday, October 19, 2005 9:57 AM
> To: Developing a hybrid router/bridge.
> Subject: Re: [rbridge] FW: Time to summarize "forward or block" BPDU 
> thread
> 
> The IS-IS Hello protocol is for electing a single unique switch per 
> link. It doesn't matter which one it is.
> 
> On the other hand, the spanning tree protocol is picking a special 
> single unique bridge per link...the one that is closest to the root.
> 
> The spanning tree algorithm is choosing a tree of shortest paths from 
> the root.
> 
> IS-IS is not trying to do that. It is just electing one guy on a link 
> to do special link-specific things.
> 
> Radia
> _______________________________________________
> rbridge mailing list
> rbridge at postel.org
> http://www.postel.org/mailman/listinfo/rbridge

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