The optional Length argument specifies the length of the test
    data part of each loop message. The maximum and minimum
    permitted values depend on the particular data link in use.
    The range is 0-4294967295.  The default length is 40.

    The optional Format argument is an octet (00-FF) which
    specifies the value of each byte in the test data part of
    each loop message.  The default results in alternating 0 and
    1 bits (55).

    loop  [node node-id] mop client client-name -
          length integer [,optional arguments...]

    Address and Circuit information loop is required for the loop
    mop client command.  If the Client cannot provide default
    Address and Circuit information, then that information must
    be specified in the command.

    loop  [node node-id] mop client -
          address lan-address, -
          circuit circuit-name, -
          length integer [,optional arguments...]

    Examples:

    loop mop client lamchp -  ! Client gives Address and Circuit
         length 20

    loop mop client mynode -  ! Client gives default Circuit
         address 08-00-2b-34-56-DD, -
         length 45