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 } | The default setting is legacy. |
Table 12: 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 containing four Selected ports | 500000 | 1400 | ||
100 Mbps | Single port | 19 | 200000 | 200 |
Aggregate interface containing two Selected ports | 100000 | 180 | ||
Aggregate interface containing three Selected ports | 66666 | 160 | ||
Aggregate interface containing four Selected ports | 50000 | 140 | ||
1000 Mbps | Single port | 4 | 20000 | 20 |
Aggregate interface containing two Selected ports | 10000 | 18 | ||
Aggregate interface containing three Selected ports | 6666 | 16 | ||
Aggregate interface containing four Selected ports | 5000 | 14 | ||
10 Gbps | Single port | 2 | 2000 | 2 |
Aggregate interface containing two Selected ports | 1000 | 1 | ||
Aggregate interface containing three Selected ports | 666 | 1 | ||
Aggregate interface containing four Selected ports | 500 | 1 | ||
20 Gbps | Single port | 1 | 1000 | 1 |
Aggregate interface containing two Selected ports | 500 | 1 | ||
Aggregate interface containing three Selected ports | 333 | 1 | ||
Aggregate interface containing four Selected ports | 250 | 1 | ||
40 Gbps | Single port | 1 | 500 | 1 |
Aggregate interface containing two Selected ports | 250 | 1 | ||
Aggregate interface containing three Selected ports | 166 | 1 | ||
Aggregate interface containing four Selected ports | 125 | 1 | ||
100 Gbps | Single port | 1 | 200 | 1 |
Aggregate interface containing two Selected ports | 100 | 1 | ||
Aggregate interface containing three Selected ports | 66 | 1 | ||
Aggregate interface containing four Selected ports | 50 | 1 |