106
Specifying a standard for the device to use when it calculates
the default path cost
CAUTION:
If you change the standard that the device uses to calculate the default path costs, you restore the
path costs to the default.
You can specify a standard for the device to use in automatic calculation for the default path cost.
The device supports the following standards:
•
dot1d-1998
—The device calculates the default path cost for ports based on IEEE 802.1d-1998.
•
dot1t
—The device calculates the default path cost for ports based on IEEE 802.1t.
•
legacy
—The device calculates the default path cost for ports based on a private standard.
When you specify a standard for the device to use when it calculates the default path cost, follow
these guidelines:
•
When it calculates the path cost for an aggregate interface, IEEE 802.1t takes into account the
number of Selected ports in its aggregation group. However, IEEE 802.1d-1998 does not take
into account the number of Selected ports. The calculation formula of IEEE 802.1t is: Path cost
= 200,000,000/link speed (in 100 kbps). The link speed is the sum of the link speed values of
the Selected ports in the aggregation group.
•
IEEE 802.1d-1998 or the private standard always assigns the smallest possible value to a
single port or aggregate interface with a speed exceeding 10 Gbps. The forwarding path
selected based on this criterion might not be the best one. To solve this problem, perform one of
the following tasks:
{
Use
dot1t
as the standard for default path cost calculation.
{
Manually set the path cost for the port (see "
Configuring path costs of ports
To specify a standard for the device to use when it calculates the default path cost:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Specify a standard for the
device to use when it
calculates the default path
costs of its ports.
stp pathcost-standard
{
dot1d-1998
|
dot1t
|
legacy
}
By default, the device uses
legacy
to calculate the default
path costs of its ports.
Table 11 Mappings between the link speed and the path cost
Link speed
Port type
Path cost
IEEE
802.1d-1998
IEEE 802.1t
Private
standard
0 N/A
65535
200000000
200000
10 Mbps
Single port
100
2000000 2000
Aggregate interface
containing two Selected
ports
1000000 1800
Aggregate interface
containing three Selected
ports
666666 1600
Aggregate interface
500000 1400
