DECnet-Plus only attempts to locate TCP/IP if the RFC 1006
    listener ports attribute set of the OSI Transport entity is
    not empty.

    To disable OSI over TCP/IP (RFC 1006) and/or DECnet over
    TCP/IP (RFC 1859), you can discontinue listening on the
    appropriate port(s).  Port 102 applies to RFC 1006, and
    Port 399 applies to RFC 1859.

    For example, this will disable both RFC 1006 and RFC 1859:

    NCL> disable osi transport
    NCL> remove osi transport rfc1006 listener ports {102,399}
    NCL> enable osi transport