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.

Ping supports five ping protocols, each with its own strengths and weaknesses. The "udp" protocol is the default. A host may be configured to respond to only a few of these protocols, or even none at all. For example, www.microsoft.com is generally alive but not pingable.

icmp

The ping() method sends an icmp echo message to the remote host (this 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 this protocol requires that the program be run as root or that the program be setuid to root.

udp

The ping() method sends 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 udp and tcp ping, a host will be reported as unreachable if it is not running the appropriate echo service. For Unix-like systems see inetd(8) for more information.

tcp

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. Once the connection is made, it is torn down immediately -- no data is actually echoed. This protocol does not require any special privileges but has highest overhead of the protocols.

stream

This is just like the tcp protocol, except that once it establishes the tcp connection, it keeps it up. Each subsequent ping request re-uses the existing connection. stream provides better performance than tcp since the connection doesn't need to be created and torn down with every ping. It is also the only protocol that will recognize that the original host is gone, even if it is immediately replaced by an identical host responding in exactly the same way. The drawback is that you can only ping one host per Ping instance. You will get an error if you neglect to call close() before trying to ping a different network device.

external

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(8) 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 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.

$p->open($host);

When you are using the stream protocol, this call pre-opens the tcp socket. It's only necessary to do this if you want to provide a different timeout when creating the connection, or remove the overhead of establishing the connection from the first ping. If you don't call open(), the connection is automatically openeed 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.

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 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 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. 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 understands all of the different kinds of ICMP packets.