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Net::Ping(3)							  Net::Ping(3)

NAME    [Toc]    [Back]

     Net::Ping - check a remote	host for reachability

SYNOPSIS    [Toc]    [Back]

	 use Net::Ping;

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

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

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

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

DESCRIPTION    [Toc]    [Back]

     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.

									Page 1

Net::Ping(3)							  Net::Ping(3)

     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    [Toc]    [Back]

     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

     $p->ping($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.

	 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.

									Page 2

Net::Ping(3)							  Net::Ping(3)

WARNING    [Toc]    [Back]

     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    [Toc]    [Back]

     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

									PPPPaaaaggggeeee 3333
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