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Net::Ping(3)
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($host);
DESCRIPTION
This module contains methods to test the reachability of remote hosts on a
network. A ping object is first created with optional parameters, a
variable number of hosts may be pinged multiple times and then the
connection is closed.
You may choose one of three different protocols to use for the ping. The
"udp" protocol is the default. Note that a live remote host may still fail
to be pingable by one or more of these protocols. For example,
www.microsoft.com is generally alive but not pingable.
With the "tcp" protocol the ping() method attempts to establish a
connection to the remote host's echo port. If the connection is
successfully established, the remote host is considered reachable. No data
is actually echoed. This protocol does not require any special privileges
but has higher overhead than the other two protocols.
Specifying the "udp" protocol causes the ping() method to send a udp packet
to the remote host's echo port. If the echoed packet is received from the
remote host and the received packet contains the same data as the packet
that was sent, the remote host is considered reachable. This protocol does
not require any special privileges.
It should be borne in mind that, for both tcp and udp ping, a host will be
reported as unreachable if it is not running the appropriate echo service.
For Unix-like systems see inetd(8) for more information.
If the "icmp" protocol is specified, the ping() method sends an icmp echo
message to the remote host, which is what the UNIX ping program does. If
the echoed message is received from the remote host and the echoed
information is correct, the remote host is considered reachable.
Specifying the "icmp" protocol requires that the program be run as root or
that the program be setuid to root.
Functions
Net::Ping->new([$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 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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