Library /sys$common/syshlp/tcpip$ucp_help.hlb SET, CONFIGURATION, INTERFACE, Qualifiers, /PRIMARY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /PRIMARY
       /NOPRIMARY

    Optional.

    For DHCP-controlled interfaces, designates the interface from
    which system-wide configuration options (such as the IP address
    of the BIND server) are used.