(Optional) Configuring the Path Cost for a Port

The STP/Rapid Spanning Tree Protocol (RSTP) path cost determines root port selection. The port from which to the root port costs the least is selected as the root port.

Context

A path cost is port-specific, which is used by STP/RSTP as a reference to select a link.

The range of the path cost value is determined by the calculation method. After the calculation method is determined, you are recommended to set a relatively small path cost value for the port at a high link rate.

Use the Huawei proprietary calculation method as an example. Different link rates correspond to default path cost values of ports. For details, see Table 1.

**Table 1** Mappings between link rates and path cost values
Link Rate	Recommended value	Recommended Value Range	Value Range
10 Mbit/s	2000	200 to 20000	1 to 200000
100 Mbit/s	200	20 to 2000	1 to 200000
1 Gbit/s	20	2 to 200	1 to 200000
10 Gbit/s	2	2 to 20	1 to 200000
Over 10 Gbit/s	1	1 to 2	1 to 200000

On a network where loops occur, you are recommended to set a relatively large path cost for the port at a low link rate. STP/RSTP puts the port with the large path cost in the Blocking state and blocks the link where this port resides.

Procedure

Run system-view
The system view is displayed.

Run stp pathcost-standard { dot1d-1998 | dot1t | legacy }

A path cost calculation method is configured.

All devices on a network must use the same calculation method for path costs.

Table2 Path cost list lists path costs defined by the IEEE 802.1D-1998 standard, IEEE 802.1T standard, and Huawei legacy standard. Different vendors use different standards.

**Table 2** Path cost list
Interface Rate	Interface Mode	Recommended STP Path Cost
Interface Rate	Interface Mode	IEEE 802.1D-1998 Standard	IEEE 802.1T Standard	Huawei Legacy Standard
0	-	65535	200,000,000	200,000
10 Mbps	Half-Duplex	100	2,000,000	2000
	Full-Duplex	99	1,999,999	1999
	Aggregated Link 2 Ports	95	1,000,000	1800
	Aggregated Link 3 Ports	95	666,666	1600
	Aggregated Link 4 Ports	95	500,000	1400
100 Mbps	Half-Duplex	19	200,000	200
	Full-Duplex	18	199,999	199
	Aggregated Link 2 Ports	15	100,000	180
	Aggregated Link 3 Ports	15	66,666	160
	Aggregated Link 4 Ports	15	50,000	140
1000 Mbps	Full-Duplex	4	20,000	20
	Aggregated Link 2 Ports	3	10,000	18
	Aggregated Link 3 Ports	3	6666	16
	Aggregated Link 4 Ports	3	5000	14
10 Gbps	Full-Duplex	2	2000	2
	Aggregated Link 2 Ports	1	1000	1
	Aggregated Link 3 Ports	1	666	1
	Aggregated Link 4 Ports	1	500	1

Run interface interface-type interface-number
The view of the Ethernet interface participating in STP calculation is displayed.

The following configuration can be configured both on a Layer 2 interface and a Layer 3 interface.
Run stp cost cost
A path cost is set for the port.
- When the Huawei proprietary calculation method is used, cost ranges from 1 to 200000.
- When the IEEE 802.1d standard method is used, cost ranges from 1 to 65535.
- When the IEEE 802.1t standard method is used, cost ranges from 1 to 2000,000,00.
Run commit
The configuration is committed.