3Com Switch 7754, Configuration Manual

Page: 261 / 940

Leaf Node Configuration 261
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:
Path cost = 200,000,/ link transmission speed,
Where the link transmission speed is the sum of the speeds of the unblocked ports
on the aggregated link, which is measured in 100 Kbps.
Configuring the path costs of ports
10 Mbps Half-duplex/Full-duplex
Aggregated link 2 ports
Aggregated link 3 ports
Aggregated link 4 ports
100
95
95
95
200,000
1,000,000
666,666
500,000
2,000
1,800
1,600
1,400
100 Mbps Half-duplex/Full-duplex
Aggregated link 2 ports
Aggregated link 3 ports
Aggregated link 4 ports
19
15
15
15
200,000
100,000
66,666
50,000
200
180
160
140
1,000
Mbps Full-duplex
Aggregated link 2 ports
Aggregated link 3 ports
Aggregated link 4 ports
4
3
3
3
200,000
10,000
6,666
5,000
20
18
16
14
10 Gbps Full-duplex
Aggregated link 2 ports
Aggregated link 3 ports
Aggregated link 4 ports
2
1
1
1
200,000
1,000
666
500
2
1
1
1
Table 192 Configure the path cost for specified ports in system view
Operation Command Description
Enter system view system-view -
Configure the path
cost for specified ports stp interface interface-list
[ instance instance-id ] cost cost
Required
A MSTP-enabled switch can
calculate path costs for all its ports
automatically.
Table 193 Configure the path cost for a port in Ethernet port view
Operation Command Description
Enter system view system-view -
Enter Ethernet port
view interface interface-type
interface-number
-
Table 191 Transmission speeds and the corresponding path costs
Transmis
sion
speed
Operation mode
(half-/full-duplex) 802.1D-1998 IEEE
802.1t
Proprietary
standard