net::ping(3)

NAME

Net::Ping - check a remote host for reachability

$Id: Ping.pm,v 1.6 2002/06/19 15:23:48 rob Exp $

SYNOPSIS

use Net::Ping;
$p = Net::Ping->new();
print "$host is alive.0 if $p->ping($host);
$p->close();
$p = Net::Ping->new("icmp");
$p->bind($my_addr);  #  Specify  source  interface  of
pings
foreach $host (@host_array)
{
    print "$host is ";
    print "NOT " unless $p->ping($host, 2);
    print "reachable.0;
    sleep(1);
}
$p->close();
$p = Net::Ping->new("tcp", 2);
#  Try  connecting to the www port instead of the echo
port
$p->{port_num} = getservbyname("http", "tcp");
while ($stop_time > time())
{
    print "$host not reachable ", scalar(localtime()),
"0
        unless $p->ping($host);
    sleep(300);
}
undef($p);
# High precision syntax (requires Time::HiRes)
$p = Net::Ping->new();
$p->hires();
($ret, $duration, $ip) = $p->ping($host, 5.5);
printf("$host  [ip: $ip] is alive (packet return time:
%.2f ms)0, 1000 * $duration)
  if $ret;
$p->close();
# For backward compatibility
print "$host is alive.0 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 four 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 a udp ping, a host will
be reported as unreachable if it is not running the appro
priate 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.

If the "external" protocol is specified, the ping() method attempts to use the "Net::Ping::External" module to ping
the remote host. "Net::Ping::External" interfaces with
your system's default "ping" utility to perform the ping,
and generally produces relatively accurate results. If
"Net::Ping::External" if not installed on your system,
specifying the "external" protocol will result in an
error.

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. Returns a success
flag. If the hostname cannot be found or there is a
problem with the IP number, the success flag returned
will be undef. Otherwise, the success flag will be 1
if the host is reachable and 0 if it is not. For most
practical purposes, undef and 0 and can be treated as
the same case. In array context, the elapsed time is
also returned. The elapsed time value will be a
float, as retuned by the Time::HiRes::time() function, if hires() has been previously called, otherwise it is returned as an integer.
$p->source_verify( { 0 | 1 } );: Allows source endpoint verification to be enabled or
disabled. This is useful for those remote destina
tions with multiples interfaces where the response may
not originate from the same endpoint that the original
destination endpoint was sent to. This only affects
udp and icmp protocol pings.; This is enabled by default.
$p->hires( { 0 | 1 } );: Causes this module to use Time::HiRes module, allowing
milliseconds to be returned by subsequent calls to
ping().; This is disabled by default.
$p->bind($local_addr);: Sets the source address from which pings will be sent.
This must be the address of one of the interfaces on
the local host. $local_addr may be specified as a
hostname or as a text IP address such as
"192.168.1.1".; If the protocol is set to "tcp", this method may be
called any number of times, and each call to the
ping() method (below) will use the most recent
$local_addr. If the protocol is "icmp" or "udp", then
bind() must be called at most once per object, and (if it is called at all) must be called before the first
call to ping() for that object.
$p->open($host);: When you are using the stream protocol, this call preopens the tcp socket. It's only necessary to do this
if you want to provide a different timeout when creat
ing the connection, or remove the overhead of estab
lishing the connection from the first ping. If you
don't call "open()", the connection is automatically
opened the first time "ping()" is called. This call
simply does nothing if you are using any protocol
other than stream.
$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 other protocols do not
require special privileges, but not all network devices
implement tcp or udp echo.

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. tcp is slightly better at indicating the health of a
system than icmp because it uses more of the networking
stack to respond.

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.

INSTALL

The latest source tree is available via cvs:: cvs -z3 -q -d :pserver:anony; mous@cvs.roobik.com.:/usr/local/cvsroot/freeware co Net-Ping
cd Net-Ping
The tarball can be created as follows:: perl Makefile.PL ; make ; make dist
The latest Net::Ping release can be found at CPAN:: $CPAN/modules/by-module/Net/
1) Extract the tarball: gtar -zxvf Net-Ping-xxxx.tar.gz
cd Net-Ping-xxxx
2) Build:: make realclean
perl Makefile.PL
make
make test
3) Install: make install
Or install it RPM Style:: rpm -ta SOURCES/Net-Ping-xxxx.tar.gz; rpm -ih RPMS/noarch/perl-Net-Ping-xxxx.rpm

AUTHORS

Current maintainer:: bbb@cpan.org (Rob Brown)
External protocol:: colinm@cpan.org (Colin McMillen)
Stream protocol:: bronson@trestle.com (Scott Bronson)
Original pingecho():: karrer@bernina.ethz.ch (Andreas Karrer)
pmarquess@bfsec.bt.co.uk (Paul Marquess)
Original Net::Ping author:: mose@ns.ccsn.edu (Russell Mosemann)

COPYRIGHT

This program is free software; you may redistribute it
and/or modify it under the same terms as Perl itself.

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