The SAP path cost is used by STP to calculate the path cost to the root bridge. The path cost in BPDUs received on the root port is incremented with the configured path cost for that SAP. When BPDUs are sent out of other egress SAPs, the newly calculated root path cost is used. These are the values used for CIST when running MSTP.
STP suggests that the path cost is defined as a function of the link bandwidth. Because SAPs are controlled by complex queuing dynamics, in the 7450 ESS, 7750 SR, and 7950 XRS the STP path cost is a purely static configuration.
The default value for SAP path cost is 10. This parameter can be modified within a range of 1 to 65535; 1 being the lowest cost.
CLI syntax:
config>service>vpls>sap>stp#
path-cost sap-path-cost