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

    Performs the same function as the callrpc routine, except that
    the call message is sent to all locally connected networks using
    the broadcast address. Each time it receives a response, this
    routine calls the eachresult routine. If eachresult returns
    zero, clnt_broadcast waits for more replies; otherwise it assumes
    success and returns RPC_SUCCESS.

                                   NOTE
       This routine uses the UDP protocol. Broadcast sockets are
       limited in size to the maximum transfer unit of the data
       link. For Ethernet, this value is 1400 bytes. For FDDI, this
       value is 4500 bytes.