User`s guide

Section II: Local and Telnet Mangement

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 a combination of a 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.

The bridge priority number can be changed on an AT-8316F or an AT-

8324 Switch. You could designate which switch on your network you

wish 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 off-

line, and assign that bridge the second lowest bridge identifier number.

Bridge priority has a range of 0 to 61440 in multiples of 4096. 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 the following table.

Table 6 Bridge Priority Value Increments

Increment

Bridge

Priority

Increment

Bridge

Priority

00832768

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