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(Rapid) Spanning Tree
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Example with fast ring detection
Figure 5-14 Example with fast ring detection
The switches in the illustrated example are arranged in such a way that two devices at the
central position are configured as the root bridge and as the backup root bridge (via the pri-
ority).
The root bridge has the lowest priority, the backup root bridge has the second lowest prior-
ity. The root bridge and the backup root bridge are connected together redundantly. The re-
maining switches are networked in several rings in a ring topology. The end points of the
rings are implemented on the root bridge and on the backup root bridge. The switch furthest
away from the root bridge has a lower priority than the default setting, e.g., 40000.
The advantage of this constellation is that the individual rings are not adversely affected in
the event of an error.
5.2.5.4 Method of operation of the Spanning Tree Protocol (STP)
Path costs
In a LAN segment, data is distributed with different speeds and methods, e.g., 100 Mbps full
duplex or 10 Mbps half duplex. The interconnection of network devices involves different
transmission bandwidths and different performance characteristics - which means there are
also different “path costs”.
“High path costs” are associated with low-performance connections, e.g., 10 Mbps half du-
plex, while “low path costs” are associated with connections with a high total transmission
speed, e.g., 100 Mbps full duplex.