The virtual port number uniquely identifies a spoke-SDP within configuration BPDUs. The internal representation of a spoke-SDP is unique to a system and has a reference space much bigger than the 12 bits definable in a configuration BPDU. STP takes the internal representation value of a spoke-SDP and identifies it with its own virtual port number that is unique to every other spoke-SDP defined on the VPLS. The virtual port number is assigned at the time that the spoke-SDP is added to the VPLS.
Because the order in which spoke-SDPs are added to the VPLS is not preserved between reboots of the system, the virtual port number may change between restarts of the STP instance. To achieve consistency after a reboot, the virtual port number can be specified explicitly.
CLI syntax:
config>service>vpls>spoke-sdp# stp
port-num number