3Com MSR 50 Series Configuration Manual page 472

472 C 23: MSTP C
HAPTER
n
c
ONFIGURATION
Table 16 Link speed vs. path cost
Link speed Duplex state
1000 Mbps Single Port
Aggregated
Link 2 Ports
Aggregated
Link 3 Ports
Aggregated
Link 4 Ports
10 Gbps Single Port
Aggregated
Link 2 Ports
Aggregated
Link 3 Ports
Aggregated
Link 4 Ports
In the calculation of the path cost value of an aggregated link, 802.1D-1998 does
not take into account the number of ports in the aggregated link. Whereas,
802.1T takes the number of ports in the aggregated link into account. The
calculation formula 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
aggregated link.
Configuring Path Costs of Ports
Follow these steps to configure the path cost of ports:
To do...
Enter system view
Enter Ethernet Enter Ethernet
interface view interface view
or port group
Enter port
view
group view
Configure the path cost of the
port(s)
CAUTION:
If you change the standard that the device uses in calculating the default path
■
cost, the port path cost value set through the stp cost command will be out of
effect.
When the path cost of a port is changed, MSTP will re-compute the role of the
■
port and initiate a state transition. If you use 0 as instance-id, you are setting
the path cost of the CIST.
802.1D-1998 802.1t
4 20,000
4 10,000
4 6,666
4 5,000
2 2,000
2 1,000
2 666
2 500
Use the command...
system-view
interface interface-type
interface-number
port-group { manual
port-group-name |
aggregation agg-id }
stp [ instance instance-id ]
cost cost
Private standard
20
18
16
14
2
1
1
1
Remarks
-
User either command
Configured in Ethernet
interface view, the setting is
effective on the current port
only; configured in port
group view, the setting is
effective on all ports in the
port group.
Optional
By default, MSTP
automatically calculates the
path cost of each port