Three Standards For Calculating Stp Path Cost On An Stp Port - H3C S9500 Series Operation Manual

Operation Manual – STP
H3C S9500 Series Routing Switches
Table 1-16 Configure the path cost of a port
Configure the path cost of a port.
Restore the default path cost of a
port.
II. Configuration in Ethernet port view
Perform the following configuration in Ethernet port view.
Table 1-17 Configure the path cost of a port
Configure the path cost of a port
Restore the default path cost of a port.
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.

1.2.12 Three Standards for Calculating STP Path Cost on an STP Port

The H3C S9500 Series Routing Switches support DOT1T calculation , DOT1D-1998
calculation and legacy path cost calculation. By default, legacy standard is applied for
S9500 series.
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
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.
Non-aggregation port
The actual rate counts.
2) Calculating the path cost
Operation
Operation
1-24
Chapter 1 MSTP Region-configuration
Command
stp interface interface-list
instance-id ] cost cost
undo stp interface interface-list [ instance
instance-id ] cost
Command
stp [ instance instance-id ] cost cost
undo stp [ instance instance-id ] cost
[ instance