Spoke-SDP priority allows a configurable tiebreaking parameter to be associated with a spoke-SDP. When configuration BPDUs are being received, the configured spoke-SDP priority is used in some circumstances to determine whether a spoke-SDP is designated or blocked.
In traditional STP implementations (802.1D-1998), this field is called the port priority and has a value of 0 to 255. This field is coupled with the port number (0 to 255 also) to create a 16-bit value. In the latest STP standard (802.1D-2004), only the upper 4 bits of the port priority field are used to encode the spoke-SDP priority. The remaining 4 bits are used to extend the port ID field into a 12-bit virtual port number field. The virtual port number uniquely references a spoke-SDP within the STP instance. See Spoke-SDP Virtual Port Number for more information about the virtual port number.
STP computes the actual spoke-SDP priority by taking the configured priority value and masking out the lower four bits. The result is the value that is stored in the spoke-SDP priority parameter. For instance, if a value of 0 was entered, masking out the lower 4 bits would result in a parameter value of 0. If a value of 255 was entered, the result would be 240.
The default value for spoke-SDP priority is 128. This parameter can be modified within a range of 0 to 255; 0 being the highest priority. Masking causes the values actually stored and displayed to be 0 to 240, in increments of 16.
CLI syntax:
config>service>vpls>spoke-sdp>stp#
priority stp-priority