3Com 4500G Series, Configuration Manual

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1-25
Table 1-7
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.