Allied Telesis AT-S82 - Manual (Page 65)

AT-S82 Management Software User’s Guide
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Table 7 lists the RSTP port costs with Auto when the port is part of a port
trunk.
Note
You cannot set the port cost manually.
Port Priority
If two paths have the same port cost, the bridges must select a preferred
path. In some instances this can involve the use of the port priority
parameter. This parameter is used as a tie breaker when two paths have
the same cost.
The range for port priority is 0 to 240. As with bridge priority, this range is
broken into increments, in this case multiples of 16. Table 8 lists the valid
port priority values. The default value is 128, which is increment 8.
Forwarding Delay and Topology Changes
If there is a change in the network topology due to a failure, removal, or
addition of any active components, the active topology also changes. This
Table 7. RSTP Auto Port Trunk Costs
Port Speed Port Cost
10 Mbps 20,000
100 Mbps 20,000
1000 Mbps 2,000
Table 8. Port Priority Value Increments
Increment
Port
Priority
Increment
Port
Priority
0 0 8 128
1 16 9 144
2 32 10 160
3 48 11 176
4 64 12 192
5 80 13 208
6 96 14 224
7 112 15 240