Allied Telesis AT-S62 - Manual (Page 331)

AT-S62 User’s Guide
Section IV: Spanning Tree Protocols 331
Bridge Priority
and the Root
Bridge
The first task that bridges running spanning tree perform is the selection
of a root bridge. A root bridge distributes network topology information
to the other network bridges and is used by the other bridges to
determine if there are redundant paths in the network.
A root bridge is selected by the bridge priority number, also referred to as
the bridge identifier, and sometimes the bridge’s MAC address. The
bridge with the lowest bridge priority number in the network is selected
as the root bridge. If two or more bridges have the same bridge priority
number, of those bridges the one with the lowest MAC address is
designated as the root bridge.
You can change the bridge priority number in the AT-S62 software. You
can designate which switch on your network you want as the root
bridge by giving it the lowest bridge priority number. You might also
consider which bridge should function as the backup root bridge in the
event you need to take the primary root bridge offline, and assign that
bridge the second lowest bridge identifier number.
The bridge priority has a range 0 to 61440 in increments of 4096. To
make this easier for you, the management software divides the range
into increments. You specify the increment that represents the desired
bridge priority value. The range is divided into sixteen increments, as
shown in Table 12.
Table 12 Bridge Priority Value Increments
Increment
Bridge
Priority
Increment
Bridge
Priority
0 0 8 32768
1 4096 9 36864
2 8192 10 40960
3 12288 11 45056
4 16384 12 49152
5 20480 13 53248
6 24576 14 57344
7 28672 15 61440