NAME
   Net::Ping - check a remote host for reachability

SYNOPSIS
       use Net::Ping;

       $p = Net::Ping->new();
       print "$host is alive.\n" if $p->ping($host);
       $p->close();

       $p = Net::Ping->new("icmp");
       foreach $host (@host_array)
       {
           print "$host is ";
           print "NOT " unless $p->ping($host, 2);
           print "reachable.\n";
           sleep(1);
       }
       $p->close();

       $p = Net::Ping->new("tcp", 2);
       while ($stop_time > time())
       {
           print "$host not reachable ", scalar(localtime()), "\n"
               unless $p->ping($host);
           sleep(300);
       }
       undef($p);

       # For backward compatibility
       print "$host is alive.\n" if pingecho($host);

DESCRIPTION
   This module contains methods to test the reachability of remote hosts on
   a network. A ping object is first created with optional parameters, a
   variable number of hosts may be pinged multiple times and then the
   connection is closed.

   You may choose one of three different protocols to use for the ping.
   With the "tcp" protocol the ping() method attempts to establish a
   connection to the remote host's echo port. If the connection is
   successfully established, the remote host is considered reachable. No
   data is actually echoed. This protocol does not require any special
   privileges but has higher overhead than the other two protocols.

   Specifying the "udp" protocol causes the ping() method to send a udp
   packet to the remote host's echo port. If the echoed packet is received
   from the remote host and the received packet contains the same data as
   the packet that was sent, the remote host is considered reachable. This
   protocol does not require any special privileges.

   If the "icmp" protocol is specified, the ping() method sends an icmp
   echo message to the remote host, which is what the UNIX ping program
   does. If the echoed message is received from the remote host and the
   echoed information is correct, the remote host is considered reachable.
   Specifying the "icmp" protocol requires that the program be run as root
   or that the program be setuid to root.

 Functions

   Net::Ping->new([$proto [, $def_timeout [, $bytes]]]);
       Create a new ping object. All of the parameters are optional. $proto
       specifies the protocol to use when doing a ping. The current choices
       are "tcp", "udp" or "icmp". The default is "udp".

       If a default timeout ($def_timeout) in seconds is provided, it is
       used when a timeout is not given to the ping() method (below). The
       timeout must be greater than 0 and the default, if not specified, is
       5 seconds.

       If the number of data bytes ($bytes) is given, that many data bytes
       are included in the ping packet sent to the remote host. The number
       of data bytes is ignored if the protocol is "tcp". The minimum (and
       default) number of data bytes is 1 if the protocol is "udp" and 0
       otherwise. The maximum number of data bytes that can be specified is
       1024.

   $p->ping($host [, $timeout]);
       Ping the remote host and wait for a response. $host can be either
       the hostname or the IP number of the remote host. The optional
       timeout must be greater than 0 seconds and defaults to whatever was
       specified when the ping object was created. If the hostname cannot
       be found or there is a problem with the IP number, undef is
       returned. Otherwise, 1 is returned if the host is reachable and 0 if
       it is not. For all practical purposes, undef and 0 and can be
       treated as the same case.

   $p->close();
       Close the network connection for this ping object. The network
       connection is also closed by "undef $p". The network connection is
       automatically closed if the ping object goes out of scope (e.g. $p
       is local to a subroutine and you leave the subroutine).

   pingecho($host [, $timeout]);
       To provide backward compatibility with the previous version of
       Net::Ping, a pingecho() subroutine is available with the same
       functionality as before. pingecho() uses the tcp protocol. The
       return values and parameters are the same as described for the
       ping() method. This subroutine is obsolete and may be removed in a
       future version of Net::Ping.

WARNING
   pingecho() or a ping object with the tcp protocol use alarm() to
   implement the timeout. So, don't use alarm() in your program while you
   are using pingecho() or a ping object with the tcp protocol. The udp and
   icmp protocols do not use alarm() to implement the timeout.

NOTES
   There will be less network overhead (and some efficiency in your
   program) if you specify either the udp or the icmp protocol. The tcp
   protocol will generate 2.5 times or more traffic for each ping than
   either udp or icmp. If many hosts are pinged frequently, you may wish to
   implement a small wait (e.g. 25ms or more) between each ping to avoid
   flooding your network with packets.

   The icmp protocol requires that the program be run as root or that it be
   setuid to root. The tcp and udp protocols do not require special
   privileges, but not all network devices implement the echo protocol for
   tcp or udp.

   Local hosts should normally respond to pings within milliseconds.
   However, on a very congested network it may take up to 3 seconds or
   longer to receive an echo packet from the remote host. If the timeout is
   set too low under these conditions, it will appear that the remote host
   is not reachable (which is almost the truth).

   Reachability doesn't necessarily mean that the remote host is actually
   functioning beyond its ability to echo packets.

   Because of a lack of anything better, this module uses its own routines
   to pack and unpack ICMP packets. It would be better for a separate
   module to be written which understands all of the different kinds of
   ICMP packets.

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