When calculating the path cost of an aggregated link, the 802.1D-1998 standard does not take the number of the ports on the aggregated link into account, whereas the 802.1T standard does. The following formula is used to calculate the path cost of an aggregated link:

Path cost = 200,000/ link transmission speed,

where ‘link transmission speed” is the sum of the speeds of all the unblocked ports on the aggregated link measured in 100 Kbps.

Configure the path cost for specific ports

Follow these steps to configure the path cost for specified ports in system view:

To do…

Use the command…

Remarks

Enter system view

System-view

 

 

 

 

stp interface interface-list

Required

Configure the path cost for

An MSTP-enabled device can

[ instance instance-id] cost

specified ports

calculate path costs for all its

cost

 

ports automatically.

 

 

 

 

 

Follow these steps to configure the path cost for a port in Ethernet port view:

To do…

Use the command…

Remarks

Enter system view

System-view

 

 

 

Enter Ethernet port view

interface interface-type

interface-number

 

 

 

 

 

 

 

Required

Configure the path cost for the

stp [ instance instance-id]

An MSTP-enabled device can

port

cost cost

calculate path costs for all its

 

 

ports automatically.

 

 

 

Changing the path cost of a port may change the role of the port and put it in state transition. Executing the stp cost command with the instance-idargument being 0 sets the path cost on the CIST for the port.

Configuration example (A)

# Configure the path cost of GigabitEthernet 1/0/1 in spanning tree instance 1 to be 2,000.

1)Perform this configuration in system view

<device> system-view

[device] stp interface GigabitEthernet1/0/1 instance 1 cost 2000

2)Perform this configuration in Ethernet port view

<device> system-view

[device] interface GigabitEthernet1/0/1 [device-GigabitEthernet1/0/1] stp instance 1 cost 2000

Configuration example (B)

#Configure the path cost of GigabitEthernet 1/0/1 in spanning tree instance 1 to be calculated by the MSTP-enabled device according to the IEEE 802.1D-1998 standard.

1)Perform this configuration in system view

<device> system-view

[device] undo stp interface GigabitEthernet1/0/1 instance 1 cost

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3Com WX3000 operation manual Configure the path cost for specific ports, Configuration example a, Configuration example B