Allied Telesis AT-S21 - Manual (Page 40)

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Menu: Bridging>spanning tree parameters
This option allows you to change the following spanning tree
parameters. The default values are:
Bridge Priority: 32768
Max Age Time: 20
Hello Time: 2
Forwarding delay: 15
Bridge Priority: The number can be from 0 to 65,535, with 0
being the highest priority. The number consists of a 2-byte
bridge priority number and a 6-byte MAC address. Bridges use
this number to determine the root bridge for a loop-free
implementation. If bridges happen to have equal priority
values, the bridge with the numerically lowest MAC address
becomes the root bridge. When the root bridge
malfunctions, the bridge with the next priority number (the
next lowest MAC address) automatically takes over as root
bridge.
Max Age Time: The aging time can be from 6-40 seconds, with
20 seconds as a default. All bridges in a bridged LAN use this
aging time to test the age of stored configuration messages
called bridge protocol data units (BPDUs).
For example, if you use the default 20, all bridges delete
current configuration messages after 20 seconds.
Note
Aging time for BPDUs is different from aging time in the MAC address
table.
Hello Time: Hello time can be from 1-10 seconds, with 2 seconds
as the default. Bridges use this parameter to determine the
time interval between generating and sending configuration
messages.
Forwarding Delay: The default is 15 seconds. The time indicates
the waiting period before a bridge changes to a new state, for
example, becomes the new root bridge after the topology
changes. If the bridge transitions too soon, not all links may
have yet adapted to the change; therefore, loops may result.
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