Starts a loop test between the loopback applications on the
    specified source and destination nodes.

    loop [node node-id] loopback application -
         name fullname [,optional arguments...]

    loop [node node-id] loopback application  -
         address tower-set [,optional arguments...]

    The node keyword specifies the node from which the loop messages
    are sent. If you omit this keyword, the test is performed from the
    node on which you issue the loop command.  The Name or Address
    argument specifies the node whose loop mirror is used to reflect
    the messages back to the originator.  Either the Name or Address
    argument is required, but not both.  The MIRRO$SERVER account on
    the remote end must have at least the NET$EXAMINE right.

    Optional arguments are:  format, length, and count.

    Examples:

    loop loopback application name -  ! The "DOMAIN:" namespace
         DOMAIN:LAMCHP.SCH.DEC.COM    !  nickname is required for IP
                                      !  fullnames

    loop loopback application name LOCAL:.LAMCHP, count 10

    loop loopback application address = {([%x0119], -
         [dna_sessioncontrolv3, number = 25], -
         [dna_nsp], -
         [dna_osinetwork, 49::00-04:AA-00-04-00-1A-10:20])}, -
         format ff, count 10