3Com 4500G Family Configuration Manual page 101

Table 1-7 Link speed vs. path cost
Link speed
0 —
Single Port
Aggregate Link 2 Ports
10 Mbps
Aggregate Link 3 Ports
Aggregate Link 4 Ports
Single Port
Aggregate Link 2 Ports
100 Mbps
Aggregate Link 3 Ports
Aggregate Link 4 Ports
Single Port
Aggregate Link 2 Ports
1000 Mbps
Aggregate Link 3 Ports
Aggregate Link 4 Ports
Single Port
Aggregate Link 2 Ports
10 Gbps
Aggregate Link 3 Ports
Aggregate Link 4 Ports
When calculating path cost for an aggregate interface, 802.1d-1998 does not take into account the
number of member ports in its aggregation group as 802.1t does. The calculation formula of 802.1t is:
Path Cost = 200,000,000/link speed (in 100 kbps), where link speed is the sum of the link speed values
of the non-blocked ports in the aggregation group.
Configuring path costs of ports
Follow these steps to configure the path cost of ports:
To do...
Enter system view
Enter Ethernet interface
view, or Layer 2
Enter
aggregate interface
interface view
view
or port group
view
Enter port group view
Configure the path cost of the ports
Duplex state
802.1d-1998
65535
100
100
100
100
19
19
19
19
4
4
4
4
2
2
2
2
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp [ instance
instance-id ] cost cost
1-25
802.1t
200,000,000
2,000,000
1,000,000
666,666
500,000
200,000
100,000
66,666
50,000
20,000
10,000
6,666
5,000
2,000
1,000
666
500
Use the command...
Private standard
200,000
2,000
1,800
1,600
1,400
200
180
160
140
20
18
16
14
2
1
1
1
Remarks
—
Required
Use either command.
Required
By default, MSTP
automatically calculates
the path cost of each port.