3Com LinkBuilder MSH User Manual page 31

Bridging 1-17
In a bridged network, a root bridge is elected to control the other
bridges. The root bridge is made aware of any active loops by
consulting the other bridges. The STAP constructs a spanning tree
which provides unique paths between all devices in the network,
and applies it by putting various bridges' ports in to a blocking
state, as shown in Figure 1-16.
Figure 1-16 Bridge Port Blocking
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