Allied Telesis AT-S62 - Manual (Page 457)

AT-S62 Menus Interface User’s Guide
Section IV: Spanning Tree Protocols 457
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.
By changing 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. There
are sixteen increments. You specify the increment that represents the
desired bridge priority value. The increments are shown in Table 10.
Table 10 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