The physical port number to be used as the primary port. The primary port is the default port to become active and the port of priority, i.e. regardless of the status of the current active port, if the primary can be used (and Redundancy is set up to activate it when it becomes available The write will NOT take effect immediately. It will wait until the NEXT time that the redundancy algorithm determines that the primary port should be used. This object is persistent. i.e., it will retain its value between powerdowns.