The LOOP command tests the connectivity path to a specific host  in
  the network by causing test blocks of  data to  be  transmitted  to
  that host.  This test is implemented by ICMP messages passed at the
  IP level.  For this reason, it is not possible to test a particular
  protocol.

  If no host_name is specified in the command then  loopback  testing
  will occur to the address associated with the local host's name.

  NOTE: this is not the same as the internet localhost, 127.0.0.1.

  Format:
    LOOP [host_name]

Additional information available:

/ADDRESS/TIMEOUT

  This qualifier is used to specify the host by its internet address
  instead of its host_name.

  Format:
    LOOP /ADDRESS=internet_address

  This qualifier specifies the number of seconds  which  may  elapse
  in waiting for a response from a remote host.  If a message is not
  received within the timeout interval, the connection to the remote
  host is not considered to be active.

  The timeout value may take a range of from 1 through 65,535.  The
  default timeout value is 5 seconds.

  Format:
    LOOP [host_name]/TIMEOUT=seconds