VMS Help TCPIP Services, Programming Interfaces, Sockets API, getservbyport(), Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 port
    The port number for which to search. This port number should be
    specified in network byte order.
 proto
    A pointer to a string containing the name of the protocol (TCP or
    UDP) for which to search.