Allied-telesis AT-S88 Manual do Utilizador descarregar pdf (Página 106)

Chapter 11: STP and RSTP

port on a bridge is typically based on port speed. The faster the port, the

lower the port cost. The exceptions to this are:

 The ports on the root bridge, where all ports have a port cost of 0.

 When a port is a member of a trunk, the port cost of each trunk

member is the auto port cost divided by the number of trunk members.

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

bridge.

Port cost also has an Auto feature. This feature allows spanning tree to

automatically set the port cost according to the speed of the port,

assigning a lower value for higher speeds. Auto is the default setting.

Table 6 lists the STP port costs with Auto.When a port is an active

member of a trunk, the port cost is equal to the auto port cost divided by

the number of ports in the trunk.

Table 6 lists the RSTP port costs with Auto.

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

trunk.

You can override Auto and set the port cost manually.

Table 5. STP Auto Port Costs

Port Speed Port Cost

10 Mbps 2,000,000

100 Mbps 200,000

1000 Mbps 20,000

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. RSTP Auto Port Trunk Costs

Port Speed Port Cost

10 Mbps 20,000

100 Mbps 20,000

1000 Mbps 2,000

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