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

    This function returns the local network address portion of a full
    internet address.
                                   NOTE
       The 64-bit return from OpenVMS Alpha systems has zero-
       extended bits in the high 32 bits of R0.