[rbridge] Minor issue in draft-touch-trill-rbridge-arch-00a.txt

[Erik Nordmark]

                              N       N---b3---N
                              |           ||
                              |           ||
                              |           h2
                              |          /| \
                              |         / N  \
                              |        /      \
                         N---h1--r4***r5******r6
                                 *   *        *
                                 *  *         *
                                 * *          *
                             N---r7***********r9-----N
                                  \          /|\
                                   \        / | \
                                    \      /  N  N
                                     \    /
                                      \  /
                                       b8
                                       |
                                       N

              Figure 3 Reorganized RBridge Ethernet link subnet

Since there might be a hub or bridge between e.g. r4 and r7 that they 
can't see (in addition to the hub it could also be a bridge which 
doesn't speak BSTP). Thus I think the RBridges must assume that the path 
between any pair of them might have nodes/stations attached, just as in 
the r7-r9 path.

I think this makes the "inside" vs. "outside" definitions not very 
helpful in terms of understanding the toplogy; we have paths between 
RBridges which carry encapsulated frames, but for those we also have a 
designated forwarder which sends unencapsulated frames out, in order to 
handle the r7,r9,b8 type topology above.

For instance, I think an RBridge must treat all its ports as external. 
In addition, a port would also be internal when the discovery protocol 
finds that there are other RBridges directly reachable over that port.

    Erik