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184 C
HAPTER
9: B
RIDGE
-W
IDE AND
B
RIDGE
P
ORT
P
ARAMETERS
Bridge Priority
The bridge priority influences the choice of the root bridge and the
designated bridge. The lower the bridge’s priority number, the more likely
it is that the bridge is chosen as the root bridge or a designated bridge.
The bridge priority value is appended as the most significant portion of a
bridge identifier. The factory default is 0x8000.
Bridge Maximum Age
The maximum age determines when the stored configuration message
information is judged to be too old and is discarded from the bridge’s
memory. If the value is too small, then STP may reconfigure the topology
too often, causing temporary loss of connectivity in the network. If the
value is too large, the network may take longer than necessary to adjust
to a new STP configuration after a topology change such as the restarting
of a bridge. A conservative value assumes a delay variance of 2 seconds
per hop. The recommended value (factory default) is 20 seconds.
Either the factory default value or a modified value that you set for
maximum age on a given module is only used if the module is selected as
the root bridge. Otherwise, the module uses the maximum age value that
is assigned to it by the root bridge via the CBPDU. The
bridge display
shows both values — the one set by the root bridge and the one
configured on the device.
Bridge Hello Time
Hello time is the period between the configuration messages that a root
bridge generates. If the probability of losing configuration messages is
high, shorten the time to make STP more robust. Alternatively, to lower
the overhead of STP, lengthen the time. The recommended value (factory
default) is 2 seconds.
Either the factory default value or a modified value that you set for hello
time on a given module is only used if the module is selected as the root
bridge. Otherwise, the module uses the value that is assigned to it by the
root bridge via the CBPDU. The
bridge display
shows both values —
the one set by the root bridge and the one configured on the device.
Bridge Forward Delay
The forward delay value specifies the amount of time that a bridge
spends in each of the listening and the learning states. This value
temporarily prevents a bridge from starting to forward data frames to and