VMS Help LANCP, SET, DEVICE parameters, Qualifiers, /SOURCE_ROUTING  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SOURCE_ROUTING (default)
       /NOSOURCE_ROUTING

    Enables source routing on the Token Ring device. If you only have
    one ring in your LAN or you use transparent bridging, use the
    /NOSOURCE_ROUTING qualifier to turn off source routing.