I'm trying to remember some of the concepts from CS 460. Below are my ramblings
on the Spanning Tree Protocol.
The question of the day is this, are my ramblings correct?
(ASCII ART START)
+--------+ MAC 0c:00:c8:33:33:33
|Bridge A| default priority:
+---||---+ 32768
port 0||
======||======================||==========||=====100baseT==
port 0|| MAC 0c:00:c8:55:55:55 port 0||MAC 0c:00:c8:44:44:44
+---||---+ default priority: +---||---+ default priority:
|Bridge B| 32768 |Bridge C| 32768
+---||---+ +---||---+
port 1|| port 1||
======||==================================||=====10baseT===
(ASCII ART END)
Hmm. What's the chances that my figure gets wacked up in transmission?
Anyway, so, AFAIK all of our bridges' ports start in a non-forwarding blocking
state and begin to exchange BPDUs. (Blocking ports can still receive BPDUs.)The
BPDU (Bridge protocol Data Unit) includes the MAC address of the bridge as well
as the bridge priority. The default bridge priority is 32,768.
The first goal is to find the root bridge.
The root bridge is the bridge with the lowest priority. If bridges have the same
priority, as in this case, then the bridge with the lowest MAC becomes the root
bridge. In our case, that would be bridge A.
All of the root bridge's ports then become designated ports (forwarding ports.)
For the non-root bridges, there will be one root port. This
designated/forwarding port offers the lowest cost path to the root bridge,
unless there are parallel bridges.
For parallel bridges, the bridge with the lowest priority wins. In this cast, I
think that ports 0 and 1 of bridge B will stay in blocking state whereas ports 0
and 1 of bridge C will become designated/forwarding ports.
Ideas?
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