3Com SuperStack 4 Configuration Manual page 240

252 C 10: RSTP C
HAPTER
Specifying the Path Cost
on a Port
Set the Priority of a
Specified Port
ONFIGURATION
By default, all the Ethernet ports are configured as non-EdgePort.
Path Cost is a parameter related with the link rate.
Specify the Path Cost on a Port
You can specify the Path Cost on a port by using the following commands.
Perform the following configuration in Ethernet Interface View.
Table 277 Specifying the Path Cost on a Port
Operation
Specify the Path Cost on a port
Restore the default Path Cost on the port
The path cost on an Ethernet port is related to the transmission rate of the link the
port connects to. The larger the link rate is, the smaller the path cost shall be. RSTP
can automatically detect the link rate and calculate the path cost for the current
Ethernet port. The configuration of path cost brings about the re-calculation of
the spanning tree. It is recommended to adopt the default value, with which RSTP
will automatically calculate the path cost of the current port.
By default, the Switch calculates the path cost directly from the link rate.
Specify the standard to be followed in Path Cost calculation
The following two standards are currently available on the Switch:
dot1d-1998: The Switch calculates the default Path Cost of a port by the IEEE
■
802.1D-1998 standard.
dot1t: The Switch calculates the default Path Cost of a port by the IEEE 802.1t
■
standard.
You can specify the intended standard by using the following commands.
Perform the following configuration in System View.
Table 278 Specifying the Standard to be Followed in Path Cost Calculation
Operation
Specify the standard to be adopted when the
Switch calculates the default Path Cost for the
connected link
Restore the default standard to be used
By default, the Switch calculates the default Path Cost of a port by the IEEE 802.1t
standard.
The port priority is an important basis to decide if the port can be a root port. In
the calculation of the spanning tree, the port with the highest priority will be
selected as the root assuming all other conditions are the same.
You can use the following command to set the priority of a specified port.
Perform the following configurations in the Ethernet Port View.
Command
cost
stp cost
undo stp cost
Command
stp pathcost-standard {
dot1d-1998 | dot1t }
undo stp pathcost-standard