Allied Telesis AT-S63 User Manual
Chapter 20: Spanning Tree and Rapid Spanning Tree Protocols
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Section V: Spanning Tree Protocols
Table 16 lists the STP port costs with Auto-Detect when a port is part of a
port trunk.
port trunk.
Table 17 lists the RSTP port costs with Auto-Detect.
Table 18 lists the RSTP port costs with Auto-Detect when the port is part
of a port trunk.
of a port trunk.
You can override Auto-Detect and 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.
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. To select a port
priority for a port, you enter the increment of the desired value. Table 19
lists the values and increments. The default value is 128, which is
increment 8.
broken into increments, in this case multiples of 16. To select a port
priority for a port, you enter the increment of the desired value. Table 19
lists the values and increments. The default value is 128, which is
increment 8.
Table 16. STP Auto-Detect Port Trunk Costs
Port Speed
Port Cost
10 Mbps
4
100 Mbps
4
1000 Mbps
2
Table 17. RSTP Auto-Detect Port Costs
Port Speed
Port Cost
10 Mbps
2,000,000
100 Mbps
200,000
1000 Mbps
20,000
Table 18. RSTP Auto-Detect Port Trunk Costs
Port Speed
Port Cost
10 Mbps
20,000
100 Mbps
20,000
1000 Mbps
2,000