Net::Ping(3) Perl Programmers Reference Guide Net::Ping(3)NAMENet::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($host);
DESCRIPTION
This module contains methods to test the reachability of
remote hosts on a network. A ping object is first created
with optional parameters, a variable number of hosts may
be pinged multiple times and then the connection is
closed.
You may choose one of three different protocols to use for
the ping. The "udp" protocol is the default. Note that a
live remote host may still fail to be pingable by one or
more of these protocols. For example, www.microsoft.com is
generally alive but not pingable.
With the "tcp" protocol the ping() method attempts to
establish a connection to the remote host's echo port. If
the connection is successfully established, the remote
host is considered reachable. No data is actually echoed.
This protocol does not require any special privileges but
has higher overhead than the other two protocols.
Specifying the "udp" protocol causes the ping() method to
send a udp packet to the remote host's echo port. If the
echoed packet is received from the remote host and the
received packet contains the same data as the packet that
was sent, the remote host is considered reachable. This
protocol does not require any special privileges.
It should be borne in mind that, for both tcp and udp
ping, a host will be reported as unreachable if it is not
running the appropriate echo service. For Unix-like sys
tems see inetd(8) for more information.
If the "icmp" protocol is specified, the ping() method
sends an icmp echo message to the remote host, which is
what the UNIX ping program does. If the echoed message is
received from the remote host and the echoed information
is correct, the remote host is considered reachable.
Specifying the "icmp" protocol requires that the program
be run as root or that the program be setuid to root.
Functions
Net::Ping->new([$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.
$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.
WARNINGpingecho() 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.
2001-02-22 perl v5.6.1 Net::Ping(3)
