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

    A client interface to the Portmapper. This routine returns the
    port number on which waits a server that supports program number
    prognum, version versnum, and speaks the transport protocol
    associated with protocol (IPPROTO_UDP or IPPROTO_TCP).

                                  NOTES
       If the requested version is not available, but at least the
       requested program is registered, the routine returns a port
       number.

       The pmap_getport routine returns the port number in host
       byte order not network byte order. For certain routines you
       may need to convert this value to network byte order using
       the htons routine. For example, the sockaddr_in structure
       requires that the port number be in network byte order.