


Net::Ping(3p)    Perl Programmers Reference Guide   Net::Ping(3p)


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. The "udp" protocol is the default. Note that a
       live remote host may still fail to be pingable by one or
       more of these protocols. For example, www.microsoft.com is
       generally alive but not pingable.

       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



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Net::Ping(3p)    Perl Programmers Reference Guide   Net::Ping(3p)


       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.

       It should be borne in mind that, for both tcp and udp
       ping, a host will be reported as unreachable if it is not
       running the appropriate echo service.  For Unix-like sys-
       tems see inetd(8) for more information.

       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 pro-
           vided, 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 sec-
           onds.

           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 num-
           ber, 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.




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Net::Ping(3p)    Perl Programmers Reference Guide   Net::Ping(3p)


       $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 imple-
       ment 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 mil-
       liseconds.  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 pack-
       ets.

       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 under-
       stands all of the different kinds of ICMP packets.





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