H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 188)

20-30
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... Use the command... Remarks
Enter system view system-view —
Enter Ethernet
interface view interface interface-type
interface-number
Enter Ethernet
interface view
or port group
view
Enter port group
view
port-group { manual
port-group-name |
aggregation
agg-id }
Required
Use either command.
Configurations made in Ethernet
interface view will take effect on the
current port only; configurations made
in port group view will take effect on all
ports in the port group.
Configure the path cost of the
port(s) stp [ instance instance-id ]
cost cost
Required
By default, MSTP automatically
calculates the path cost of each port.
z
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.
z
When the path cost of a port is changed, MSTP will re-calculate 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.
Configuring Port Priority
The priority of a port is an import basis that determines whether the port can be elected as the root port
of device. If all other conditions are the same, the port with the highest priority will be elected as the root
port.
On an MSTP-compliant device, a port can have different priorities in different MST instances, and the
same port can play different roles in different MST instances, so that data of different VLANs can be
propagated along different physical paths, thus implementing per-VLAN load balancing. You can set
port priority values based on the actual networking requirements.
Configuration procedure
Follow these steps to configure the priority of a port or a group of ports: