3Com 4210 9-Port Configuration Manual page 232

Rate
Half-duplex/Full-duplex
Aggregated link 2 ports
10 Mbps
Aggregated link 3 ports
Aggregated link 4 ports
Half-duplex/Full-duplex
Aggregated link 2 ports
100 Mbps
Aggregated link 3 ports
Aggregated link 4 ports
Full-duplex
Aggregated link 2 ports
1,000 Mbps
Aggregated link 3 ports
Aggregated link 4 ports
Full-duplex
Aggregated link 2 ports
10 Gbps
Aggregated link 3 ports
Aggregated link 4 ports
Normally, the path cost of a port operating in full-duplex mode is slightly less than that of the port
operating in half-duplex mode.
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:
Where, "link transmission rate" is the sum of the rates 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...
Enter system view
Configure the path cost for
specified ports
Operation mode
(half-/full-duplex)
Path cost = 200,000,000 / link transmission rate
Use the command...
system-view
stp interface interface-list
[ instance instance-id ] cost
cost
1-31
802.1D-1998 IEEE 802.1t
100 2,000,000
95 1,000,000
95 666,666
95 500,000
19 200,000
15 100,000
15 66,666
15 50,000
4 20,000
3 10,000
3 6,666
3 5,000
2 2,000
1 1,000
1 666
1 500
—
Required
An MSTP-enabled switch can
calculate path costs for all its
ports automatically.
Latency
standard
2,000
1,800
1,600
1,400
200
180
160
140
20
18
16
14
2
1
1
1
Remarks