Library /sys$common/syshlp/nclhelp.hlb set, routing, phaseiv_prefix  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Support: All
    Default: Hex 49        Value: Address prefix

    Prefix for Phase IV addresses. If the characteristic phase iv
    address is not 0.0, a DECnet area address is formed by adding
    the area portion of the Phase IV address to this prefix.
    You can modify this characteristic only when the entity is
    disabled.

    set [node node-id] routing phaseiv prefix address-prefix

    Example:

    set routing phaseiv prefix = 49::