VMS Help TCPIP Services, Programming Interfaces, RPC Portmapper Routines, pmap_set, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 prognum
    The program number associated with the server procedure.
 versnum
    The version number associated with the server procedure.
 protocol
    The transport protocol that the server procedure uses. Specify
    either IPPROTO_UDP or IPPROTO_TCP.
 port
    The port number associated with the server program.