3Com 4500 PWR 26-Port Configuration Manual page 261

Rate
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
Follow these steps to configure the path cost for a port in Ethernet port view:
To do...
Enter system view
Enter Ethernet port view
Configure the path cost for the
port
Changing the path cost of a port may change the role of the port and put it in state transition. Executing
the stp cost command with the instance-id argument being 0 sets the path cost on the CIST for the port.
Configuration example (A)
# Configure the path cost of Ethernet 1/0/1 in MSTI 1 to be 2,000.
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
Use the command...
system-view
interface interface-type
interface-number
stp [ instance instance-id ]
cost cost
20-31
802.1D-1998 IEEE 802.1t
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.
—
—
Required
An MSTP-enabled switch can
calculate path costs for all its
ports automatically.
Latency
standard
20
18
16
14
2
1
1
1
Remarks
Remarks