3Com Switch 8800 Configuration Guide Chapter 38 MSTP Region-configuration
38-24
I. Configuration in system view
Perform the following configuration in system view.
Table 38-15 Configure the path cost of a port
Operation Command
Configure the path cost of a port. stp interface interface-list [ instance
instance-id ] cost cost
Restore the default path cost of a port. undo stp interface interface-list
[ instance instance-id ] cost
II. Configuration in Ethernet port view
Perform the following configuration in Ethernet port view.
Table 38-16 Configure the path cost of a port
Operation Command
Configure the path cost of a port stp [ instance instance-id ] cost cost
Restore the default path cost of a port. undo stp [ instance instance-id ] cost
You can configure the path cost of a port with either of the earlier-mentioned measures.
Upon the change of path cost of a port, MSTP will recalculate the port role and transit
the state. When instance-id takes 0, it indicates to set the path cost on the CIST.
By default, MSTP is responsible for calculating the path cost of a port.
38.2.12 STP Path Cost Calculation Standards on STP port The Switch 8800 uses its own legacy path calculation but both DOT1T and
DOT1D-1998 path cost calculation can be used, as well. By default, the DOT1T is
applied.
The port rate must be obtained first before calculating the path cost of a port as the path
cost is associated with the port rate. The three standards use their own way to work out
the port rate, based on which each standard calculates the path cost of the by certain
algorithm.
I. DOT1T calculation standard
1) Calculating the rate
z Aggregation port
The rate of either a primary or a secondary port in an aggregation port group is the sum
of the port rates in the group. If a port is down, the rate is 0.
z Non-aggregation port