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Each bridge in a network that supports STP performs one of three functions (as determined by
STP):
Root Bridge. There is only one root bridge in the network. This bridge forwards
traffic between the two subnets it connects. It is also the starting bridge for determining
which of the other bridges in the network are forwarding bridges and which are backup
bridges.
Forwarding Bridge. Forwarding bridges are the active bridges in the network that
forward traffic between subnets. There can be only one active path between the same
two subnets.
In figure 6-2, Bridge 1 is the forwarding bridge between subnets A and C, and Bridge 2
between subnets A and B. Traffic between subnets B and C is handled by Bridges 1
and 2. Bridge 3 is a backup bridge in this configuration.
Note
The IEEE, for Spanning Tree Protocol support, recommends that there are no
more than seven forwarding bridges in the active path between any two nodes in
the network.
The actual limit for your network depends on the amount and type of traffic
being transmitted. With careful network and traffic analysis, the number of
bridges could be higher, but one of the goals of a good network design should be
to minimize the number of bridges between any two nodes that wish to
communicate.
The HP 10:10 LAN Bridge MB is pre-configured with the IEEE recommended
values for the STP parameters. To extend your network beyond the
seven-bridge limit without encountering errors due to excessive transmission
times, you may need to modify the STP parameters. Such modification can be
performed through HP network management products. See your network
management product documentation for details.
How the Bridge Works 6-7
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