3Com 4510G - Page 92

4-25
Table 4-7 Link speed vs. path cost
Link speed Duplex state 802.1d-1998 802.1t Private standard
0 — 65535 200,000,000 200,000
10 Mbps
Single Port
Aggregate Link 2 Ports
Aggregate Link 3 Ports
Aggregate Link 4 Ports
100
100
100
100
2,000,000
1,000,000
666,666
500,000
2,000
1,800
1,600
1,400
100 Mbps
Single Port
Aggregate Link 2 Ports
Aggregate Link 3 Ports
Aggregate Link 4 Ports
19
19
19
19
200,000
100,000
66,666
50,000
200
180
160
140
1000 Mbps
Single Port
Aggregate Link 2 Ports
Aggregate Link 3 Ports
Aggregate Link 4 Ports
4
4
4
4
20,000
10,000
6,666
5,000
20
18
16
14
10 Gbps
Single Port
Aggregate Link 2 Ports
Aggregate Link 3 Ports
Aggregate Link 4 Ports
2
2
2
2
2,000
1,000
666
500
2
1
1
1
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... Use the command... Remarks
Enter system view system-view —
Enter Ethernet interface
view, or Layer 2
aggregate interface
view
interface interface-type
interface-number
Enter
interface view
or port group
view
Enter port group view
port-group manual
port-group-name
Required
Use either command.
Configure the path cost of the ports
stp [ instance
instance-id ] cost cost
Required
By default, MSTP
automatically calculates
the path cost of each port.