87Link speed Port type Path costIEEE 802.1d-1998 IEEE 802.1t Private standard10 GbpsSingle port22000 2Aggregate interfacecontaining 2 Selected ports 1000 1Aggregate interfacecontaining 3 Selected ports 666 1Aggregate interfacecontaining 4 Selected ports 500 1Configuration restrictions and guidelines• When it calculates path cost for an aggregate interface, IEEE 802.1t takes into account the numberof Selected ports in its aggregation group, but IEEE 802.1d-1998 does not. The calculation formulaof IEEE 802.1t is: Path cost = 200,000,000/link speed (in 100 kbps), where link speed is the sumof the link speed values of the Selected ports in the aggregation group.• When multiple ports operate at a rate higher than 10 Gbps and the standard for default path costcalculation is dot1d-1998 or legacy, the path cost of a single port or an aggregate interface takesthe smallest value. As a result, the forwarding path selected might not be optimal. To solve thisproblem, use dot1t as the standard for default path cost calculation, or manually set the path costfor a port (see "Configuring path costs of ports").Configuration procedureTo specify a standard for the device to use when it calculates the default path cost:Step Command Remarks1. Enter system view. system-view N/A2. Specify a standard for thedevice to use when itcalculates the default pathcosts of its ports.stp pathcost-standard{ dot1d-1998 | dot1t | legacy }Optional.legacy by default.Configuring path costs of portsWhen the path cost of a port changes, the system re-calculates the role of the port and initiates a statetransition.To configure the path cost of ports:Step Command Remarks1. Enter system view. system-view N/A2. Enter interface view or portgroup view.• Enter Layer 2 Ethernet interface view orLayer 2 aggregate interface view:interface interface-typeinterface-number• Enter port group view:port-group manual port-group-nameUse one of the commands.
