Allied Telesis AT-S63 - Manual (Page 251)

AT-S63 Management Software Menus Interface User’s Guide
Section II: Advanced Features 251
Bridge Priority
and the Root
Bridge
The first task that bridges perform when a spanning tree protocol is
activated on a network 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-S63 management
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 AT-S63 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