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

[Larry Kreeger (kreeger)]

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