/sys$common/syshlp/helplib.hlb LANCP, SET, DEVICE parameters, Qualifiers, /FULL_DUPLEX  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /FULL_DUPLEX
       /NOFULL_DUPLEX (default)

    Enables full-duplex operation of a LAN device. Before full-duplex
    operation results from the use of this qualifier, additional
    device or network hardware setup may be required. Some devices
    may be enabled for full-duplex operation by default. Some devices
    may not allow the setting to be changed.

    The /NOFULL_DUPLEX qualifier, disables full-duplex operation.