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 circuit circuit-name -
          address lan-address, -
          format octet [,optional arguments...]

    If an Address is not supplied in the command on a LAN circuit,
    then the Client argument must be specified so the address
    information can be obtained from the MOP Client database.

    loop  [node node-id] mop circuit circuit-name -
          client client-name, -
          format octet [,optional arguments...]

    Examples:

    loop mop circuit csmacd-1 address 08-00-2b-00-13-4F, format FF

    loop mop circuit fddi-1 -
         client mynode, format 00  ! Client gives default Address