Allied Telesis AT-S82, User Manual

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AT-S82 Management Software User’s Guide
59
You can change the bridge priority number in the AT-S82 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-S82 management software divides the range
into increments. The valid range is of sixteen increments is shown in
Table 3.
Path Costs and Port Costs
After the root bridge has been selected, the bridges must determine if the
network contains redundant paths and, if one is found, they must select a
preferred path while placing the redundant paths in a backup or blocking
state.
Where there is only one path between a bridge and the root bridge, the
bridge is referred to as the
designated bridge and the port through which
the bridge is communicating with the root bridge is referred to as the root
port .
If redundant paths exist, the bridges that are a part of the paths must
determine which path will be the primary, active path, and which path(s)
will be placed in the standby, blocking mode. This is accomplished by an
determination of
path costs . The path offering the lowest cost to the root
bridge becomes the primary path and all other redundant paths are placed
into blocking state.
Path cost is determined through an evaluation of port costs . Every port on
Table 3. 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