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), where 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 an aggregate interface when the link speed of the port or interface exceeds 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 9: 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

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