Allied Telesis AT-GS950/8 - Manual (Page 113)

AlliedWare Plus Version 2.1.2 Management Software Web Browser User’s Guide
113
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 lowest bridge priority
number, the one with the lowest MAC address is designated as the root
bridge.
You can change the bridge priority number in the AT-S107 Management
software. You can designate which switch on your network as the root
bridge by giving it the lowest bridge priority number. You may also
consider which bridge should function as the backup root bridge in the
event you need to take the primary root bridge off line 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-S107 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 1.
Table 1 Bridge Priority Value Increments
Increment
Bridge
Priority
Increment
Bridge
Priority
0x0000 0 0x8000 32768
0x1000 4096 0x9000 36864
0x2000 8192 0xA000 40960
0x3000 12288 0xB000 45056
0x4000 16384 0xC000 49152
0x5000 20480 0xD000 53248
0x6000 24576 0xE000 57344
0x7000 28672 0xF000 61440