Allied Telesis AT-GS950/8 manual Port Speed, Port Cost

Chapter 8: Spanning Tree Protocol (STP)

a bridge participating in STP has a cost associated with it. The cost of a port on a bridge is typically based on port speed. The faster the port, the lower the port cost. The exception to this is the ports on the root bridge, where all ports have a port cost of 0.

Path cost is simply the sum of the port costs between a bridge and the root bridge.

The AT-GS950/8 WebSmart switch automatically sets the port cost according to the speed of the port, assigning a lower value for higher speeds. Table 6 lists the STP port costs.

Table 4. STP Port Costs

Port Speed	Port Cost
10 Mbps	100
100 Mbps	10
1000 Mbps	4

Table 5 lists the STP port costs with Auto when a port is part of a port trunk.

Table 5. STP Auto-Detect Port Trunk Costs

Port Speed	Port Cost
10 Mbps	4
100 Mbps	4
1000 Mbps	2

Table 6 lists the RSTP port costs with Auto.

Table 6. RSTP Auto Port Costs

Port Speed	Port Cost
10 Mbps	2,000,000
100 Mbps	200,000
1000 Mbps	20,000

Table 7 lists the RSTP port costs with Auto when the port is part of a port

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