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Net::Ping

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

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 remotehosts on a network. A ping object is first created with optionalparameters, a variable number of hosts may be pinged multipletimes 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 aconnection to the remote host's echo port. If the connection issuccessfully established, the remote host is considered reachable. Nodata is actually echoed. This protocol does not require any specialprivileges but has higher overhead than the other two protocols.

Specifying the ``udp'' protocol causes the ping() method to send a udppacket to the remote host's echo port. If the echoed packet isreceived from the remote host and the received packet contains thesame data as the packet that was sent, the remote host is consideredreachable. This protocol does not require any special privileges.

If the ``icmp'' protocol is specified, the ping() method sends an icmpecho message to the remote host, which is what the UNIX ping programdoes. If the echoed message is received from the remote host andthe echoed information is correct, the remote host is consideredreachable. Specifying the ``icmp'' protocol requires that the programbe 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. $protospecifies the protocol to use when doing a ping. The current choicesare ``tcp'', ``udp'' or ``icmp''. The default is ``udp''.

If a default timeout ($def_timeout) in seconds is provided, it is usedwhen a timeout is not given to the ping() method (below). The timeoutmust 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 bytesare included in the ping packet sent to the remote host. The number ofdata bytes is ignored if the protocol is ``tcp''. The minimum (anddefault) number of data bytes is 1 if the protocol is ``udp'' and 0otherwise. The maximum number of data bytes that can be specified is1024.

$p->ping($host [, $timeout]);

Ping the remote host and wait for a response. $host can be either thehostname or the IP number of the remote host. The optional timeoutmust be greater than 0 seconds and defaults to whatever was specifiedwhen the ping object was created. If the hostname cannot be found orthere 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 allpractical purposes, undef and 0 and can be treated as the same case.

$p->close();

Close the network connection for this ping object. The networkconnection is also closed by ``undef $p''. The network connection isautomatically closed if the ping object goes out of scope (e.g. $p islocal to a subroutine and you leave the subroutine).

pingecho($host [, $timeout]);

To provide backward compatibility with the previous version ofNet::Ping, a pingecho() subroutine is available with the samefunctionality as before. pingecho() uses the tcp protocol. Thereturn values and parameters are the same as described for the ping()method. This subroutine is obsolete and may be removed in a futureversion of Net::Ping.

WARNING

pingecho() or a ping object with the tcp protocol use alarm() toimplement the timeout. So, don't use alarm() in your program whileyou are using pingecho() or a ping object with the tcp protocol. Theudp and icmp protocols do not use alarm() to implement the timeout.

NOTES

There will be less network overhead (and some efficiency in yourprogram) if you specify either the udp or the icmp protocol. The tcpprotocol will generate 2.5 times or more traffic for each ping thaneither udp or icmp. If many hosts are pinged frequently, you may wishto implement a small wait (e.g. 25ms or more) between each ping toavoid flooding your network with packets.

The icmp protocol requires that the program be run as root or that itbe setuid to root. The tcp and udp protocols do not require specialprivileges, but not all network devices implement the echo protocolfor 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 orlonger to receive an echo packet from the remote host. If the timeoutis set too low under these conditions, it will appear that the remotehost is not reachable (which is almost the truth).

Reachability doesn't necessarily mean that the remote host is actuallyfunctioning beyond its ability to echo packets.

Because of a lack of anything better, this module uses its ownroutines to pack and unpack ICMP packets. It would be better for aseparate module to be written which understands all of the differentkinds of ICMP packets.

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