Net::Ping

See the current Perl documentation for Net::Ping.

Here is our local, out-dated (pre-5.6) version:

Net::Ping - check a remote host for reachability

    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)

    

    

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.


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.