Allied Telesis AT-S60 - Manual (Page 189)

Chapter 12: STP, RSTP, and MSTP
Section II: Local and Telnet Management 188
The port costs of the ports on an AT-8400 Series switch can be adjusted
through the management software. For STP and RSTP, the range is 0 to
200,000,000.
The default value of 0 activates auto-detection. This features sets port
cost according to port speed, assigning lower costs to ports operating at
higher speeds.
Table 6 lists the auto-detection default values for STP and RSTP.
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 can be used as a tie-breaker when two paths
have the same cost.
Table 6 STP and RSTP Auto-Detect Port Costs
Port Speed Port Cost
10 Mbps 2000000
100 Mbps 200000
1000 Mbps 20000