Spanning Tree
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3.3 Examples
UM RedundConfig RSPL
Release 2.0 02/2013
3.3.2 Example of manipulating the root path
You can use the network plan
(see fig. 23)
to follow the flow chart
(see
fig. 21)
for determining the root path. The Administrator has performed the
following:
– Left the default value of 32,768 (8000H) for every bridge apart from bridge
1 and bridge 5, and
– assigned to bridge 1 the value 16,384 (4000H), thus making it the root
bridge.
– To bridge 5 he assigned the value 28,672 (7000H).
In the example, all the sub-paths have the same path costs. The protocol
blocks the path between bridge 2 and bridge 3 as a connection from bridge 3
via bridge 2 to the root bridge would mean higher path costs.
The path from bridge 6 to the root bridge is interesting:
The path via bridge 5 and bridge 3 creates the same root path costs as
the path via bridge 4 and bridge 2.
The bridges select the path via bridge 4 because the value 28,672 for the
priority in the bridge identifier is smaller than value 32,768.
Note:
Because the Administrator does not change the default values for the
priorities of the bridges in the bridge identifier, apart from the value for the
root bridge, the MAC address in the bridge identifier alone determines which
bridge becomes the new root bridge if the current root bridge goes down.
