Net::Ping(3) 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($host);
DESCRIPTION
This module contains methods to test the reachability of remote hosts on
a network. A ping object is first created with optional parameters, a
variable number of hosts may be pinged multiple times and then the
connection is closed.
You may choose one of three different protocols to use for the ping.
With the "tcp" protocol the ping() method attempts to establish a
connection to the remote host's echo port. If the connection is
successfully established, the remote host is considered reachable. No
data is actually echoed. This protocol does not require any special
privileges but has higher overhead than the other two protocols.
Specifying the "udp" protocol causes the ping() method to send a udp
packet to the remote host's echo port. If the echoed packet is received
from the remote host and the received packet contains the same data as
the packet that was sent, the remote host is considered reachable. This
protocol does not require any special privileges.
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If the "icmp" protocol is specified, the ping() method sends an icmp echo
message to the remote host, which is what the UNIX ping program does. If
the echoed message is received from the remote host and the echoed
information is correct, the remote host is considered reachable.
Specifying the "icmp" protocol requires that the program be run as root
or that the program be setuid to root.
Functions
Net::Ping->new([$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.
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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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