3Com Switch 4200G Configuration Guide

Leaf Node Configuration 133
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 = 200,000,000 / link transmission speed
Here 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
Changing the path cost of a port may change the role of the port and put it in state
transition. If you execute the stp cost command with the instance-id argument being
0, the path cost you set is for the CIST.
Configuration example (A)
1 Configure the path cost of GigabitEthernet1/0/1 port in spanning tree instance 1 to
be 2,000.
■ Configure in system view.
<S4200G> system-view
System View: return to User View with Ctrl+Z.
[4200G] stp interface GigabitEthernet1/0/1 instance 1 cost 2000
10 Gbps Full-duplex
Aggregated link 2 ports
Aggregated link 3 ports
Aggregated link 4 ports
2
1
1
1
2,000
1,000
666
500
2
1
1
1
Table 105 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 106 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
—
Configure the path
cost for the port
stp [ instance instance-id ] cost
cost
Required
A MSTP-enabled switch can
calculate path costs for all its ports
automatically.
Table 104 Transmission speeds and the corresponding path costs (Continued)
Transmiss
ion speed
Operation mode
(half-/full-duplex)
802.1D-1998 IEEE 802.1t
Standard
defined by 3Com