Allied Telesis AT-GS950/48PS, AT-S111 manual Bridge Priority Root, Increment Bridge Priority

Bridge Priority

and the Root

Bridge

AT-GS950/48PS Switch Web Interface User’s Guide

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-S111 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-S111 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	Increment	Bridge
	Priority		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

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