package Net::Ping;
-# Current maintainer: colinm@cpan.org (Colin McMillen)
-# stream protocol: bronson@trestle.com (Scott Bronson)
-#
-# Original author: mose@ccsn.edu (Russell Mosemann)
-#
-# Authors of the original pingecho():
-# karrer@bernina.ethz.ch (Andreas Karrer)
-# Paul.Marquess@btinternet.com (Paul Marquess)
-#
-# Copyright (c) 2001, Colin McMillen. All rights reserved. This
-# program is free software; you may redistribute it and/or modify it
-# under the same terms as Perl itself.
-use 5.006_001;
+# $Id: Ping.pm,v 1.5 2001/11/19 09:44:18 rob Exp $
+
+require 5.002;
require Exporter;
use strict;
-our(@ISA, @EXPORT, $VERSION, $def_timeout, $def_proto, $max_datasize);
+use vars qw(@ISA @EXPORT $VERSION
+ $def_timeout $def_proto $max_datasize);
use FileHandle;
use Socket qw( SOCK_DGRAM SOCK_STREAM SOCK_RAW PF_INET
- inet_aton inet_ntoa sockaddr_in );
+ inet_aton sockaddr_in );
use Carp;
@ISA = qw(Exporter);
@EXPORT = qw(pingecho);
-$VERSION = 2.04;
+$VERSION = 2.06;
# Constants
bless($self, $class);
$proto = $def_proto unless $proto; # Determine the protocol
- croak('Protocol for ping must be "icmp", "udp", "tcp", "stream", or "external"')
- unless $proto =~ m/^(icmp|udp|tcp|stream|external)$/;
+ croak("Protocol for ping must be \"tcp\", \"udp\" or \"icmp\"")
+ unless $proto =~ m/^(tcp|udp|icmp)$/;
$self->{"proto"} = $proto;
$timeout = $def_timeout unless $timeout; # Determine the timeout
}
elsif ($self->{"proto"} eq "icmp")
{
- croak("icmp ping requires root privilege") if ($> and $^O ne 'VMS');
+ croak("icmp ping requires root privilege") if $>;
$self->{"proto_num"} = (getprotobyname('icmp'))[2] ||
croak("Can't get icmp protocol by name");
$self->{"pid"} = $$ & 0xffff; # Save lower 16 bits of pid
socket($self->{"fh"}, &PF_INET(), &SOCK_RAW(), $self->{"proto_num"}) ||
croak("icmp socket error - $!");
}
- elsif ($self->{"proto"} eq "tcp" || $self->{"proto"} eq "stream")
+ elsif ($self->{"proto"} eq "tcp") # Just a file handle for now
{
$self->{"proto_num"} = (getprotobyname('tcp'))[2] ||
croak("Can't get tcp protocol by name");
# Description: Ping a host name or IP number with an optional timeout.
# First lookup the host, and return undef if it is not found. Otherwise
-# perform the specific ping method based on the protocol. Return the
+# perform the specific ping method based on the protocol. Return the
# result of the ping.
sub ping
$ip = inet_aton($host);
return(undef) unless defined($ip); # Does host exist?
- # Dispatch to the appropriate routine.
- return $self->ping_external($ip, $timeout) if $self->{"proto"} eq "external";
- return $self->ping_udp($ip, $timeout) if $self->{"proto"} eq "udp";
- return $self->ping_icmp($ip, $timeout) if $self->{"proto"} eq "icmp";
- return $self->ping_tcp($ip, $timeout) if $self->{"proto"} eq "tcp";
- return $self->ping_stream($ip, $timeout) if $self->{"proto"} eq "stream";
-
- croak("Unknown protocol \"$self->{proto}\" in ping()");
-}
-
-# Uses Net::Ping::External to do an external ping.
-sub ping_external {
- my ($self,
- $ip, # Packed IP number of the host
- $timeout # Seconds after which ping times out
- ) = @_;
-
- eval { require Net::Ping::External; };
- croak('Protocol "external" not supported on your system: Net::Ping::External not found') if $@;
- return Net::Ping::External::ping(ip => $ip, timeout => $timeout);
+ if ($self->{"proto"} eq "udp")
+ {
+ $ret = $self->ping_udp($ip, $timeout);
+ }
+ elsif ($self->{"proto"} eq "icmp")
+ {
+ $ret = $self->ping_icmp($ip, $timeout);
+ }
+ elsif ($self->{"proto"} eq "tcp")
+ {
+ $ret = $self->ping_tcp($ip, $timeout);
+ }
+ else
+ {
+ croak("Unknown protocol \"$self->{proto}\" in ping()");
+ }
+ return($ret);
}
sub ping_icmp
);
$len_msg = length($msg);
- $num_short = int($len_msg / 2);
+ $num_short = $len_msg / 2;
$chk = 0;
foreach $short (unpack("S$num_short", $msg))
{
$chk += $short;
} # Add the odd byte in
- $chk += (unpack("C", substr($msg, $len_msg - 1, 1)) << 8) if $len_msg % 2;
+ $chk += unpack("C", substr($msg, $len_msg - 1, 1)) if $len_msg % 2;
$chk = ($chk >> 16) + ($chk & 0xffff); # Fold high into low
return(~(($chk >> 16) + $chk) & 0xffff); # Again and complement
}
-# Warning: this method may generate false positives.
-# It is meant to be a private method and should only
-# be invoked by ping_tcp() if $^O =~ /win32/i.
-
-sub _ping_tcp_win
-{
- my ($self,
- $ip, # Packed IP number of the host
- ) = @_;
- my ($saddr, # sockaddr_in with port and ip
- $ret # The return value
- );
-
- socket($self->{"fh"}, &PF_INET(), &SOCK_STREAM(), $self->{"proto_num"}) ||
- croak("tcp socket error - $!");
-
- $saddr = sockaddr_in($self->{"port_num"}, $ip);
-
- $ret = 0; # Default to unreachable
-
- eval { $ret = connect($self->{"fh"}, $saddr) };
-
- # If the remote host exists but returns "Connection refused",
- # the call to connect() sets $! to "Unknown error". So, we
- # assume that an "Unknown error" actually means the host is
- # alive. This assumption may occassionally give false positives.
- $ret = 1 if $! =~ /Unknown error/i;
-
- $self->{"fh"}->close();
- return $ret;
-}
-
-# Buggy Winsock API doesn't allow us to use non-blocking connect()
-# calls. Hence, if our OS is Windows, we need to create a new process
-# to run a blocking connect attempt, and kill it after the timeout has
-# passed. Unfortunately, this won't work with the stream protocol.
-
-sub ping_tcp_win32
-{
- my ($self,
- $ip, # Packed IP number of the host
- $timeout # Seconds after which open times out
- ) = @_;
-
- socket($self->{"fh"}, &PF_INET(), &SOCK_STREAM(), $self->{"proto_num"}) ||
- croak("tcp socket error - $!");
-
- my $saddr = sockaddr_in($self->{"port_num"}, $ip);
-
- my ($child, $ret, $pid, $time);
- my $host = inet_ntoa($ip);
-
- # The code we will be executing in our new process.
- my $code = '"use Net::Ping; $p = Net::Ping->new(\'tcp\'); ';
- $code .= 'exit($p->_ping_tcp_win(' . $host . '))"';
-
- # Call the process.
- $pid = system(1, "perl", "-e", $code);
-
- # Import the POSIX version of <sys/wait.h>
- require POSIX;
- import POSIX qw(:sys_wait_h);
-
- # Get the current time; will be used to tell if we've timed out.
- $time = time;
-
- # Wait for the child to return or for the timeout to expire.
- do {
- $child = waitpid($pid, &WNOHANG());
- $ret = $?;
- } until time > ($time + $timeout) or $child;
-
- # Return an appropriate value; 0 if the child didn't return,
- # the return value of the child otherwise.
- return $ret >> 8 if $child;
-
- kill $pid;
- return 0;
-}
-
-# This writes the given string to the socket and then reads it
-# back. It returns 1 on success, 0 on failure.
-sub tcp_echo
-{
- my $self = shift;
- my $timeout = shift;
- my $pingstring = shift;
-
- my $ret = undef;
- my $time = time;
- my $wrstr = $pingstring;
- my $rdstr = "";
-
- eval <<'EOM';
- do {
- my $rin = "";
- vec($rin, $self->{"fh"}->fileno(), 1) = 1;
-
- my $rout = undef;
- if($wrstr) {
- $rout = "";
- vec($rout, $self->{"fh"}->fileno(), 1) = 1;
- }
-
- if(select($rin, $rout, undef, ($time + $timeout) - time())) {
-
- if($rout && vec($rout,$self->{"fh"}->fileno(),1)) {
- my $num = syswrite($self->{"fh"}, $wrstr);
- if($num) {
- # If it was a partial write, update and try again.
- $wrstr = substr($wrstr,$num);
- } else {
- # There was an error.
- $ret = 0;
- }
- }
-
- if(vec($rin,$self->{"fh"}->fileno(),1)) {
- my $reply;
- if(sysread($self->{"fh"},$reply,length($pingstring)-length($rdstr))) {
- $rdstr .= $reply;
- $ret = 1 if $rdstr eq $pingstring;
- } else {
- # There was an error.
- $ret = 0;
- }
- }
-
- }
- } until time() > ($time + $timeout) || defined($ret);
-EOM
-
- return $ret;
-}
-
-sub tcp_connect
-{
- my ($self,
- $ip, # Packed IP number of the host
- $timeout # Seconds after which open times out
- ) = @_;
-
- # Should we go back to using blocking IO and alarms to implement
- # the stream protocol on win32?
- croak "no nonblocking io -- can't stream ping on win32"
- if ($^O =~ /win32/i);
-
- $self->{"ip"} = $ip;
-
- socket($self->{"fh"}, &PF_INET(), &SOCK_STREAM(), $self->{"proto_num"}) ||
- croak("tcp socket error - $!");
-
- my $saddr = sockaddr_in($self->{"port_num"}, $ip);
- my $ret = 0;
-
- # Try a non-blocking TCP connect to the remote echo port.
- # Our call to select() below will stop after the timeout has
- # passed or set the return value to true if the connection
- # succeeds in time.
- $self->{"fh"}->blocking(0);
- connect($self->{"fh"}, $saddr);
-
- # This replaces the breakage where we were listening on a
- # socket that would never produce any data. This works, but
- # it's now quite a bit heavier than the old Net::Ping. I'd
- # like to see it reverted.
- return $self->tcp_echo($timeout, "ping!\n");
-}
-
# Description: Perform a tcp echo ping. Since a tcp connection is
# host specific, we have to open and close each connection here. We
# can't just leave a socket open. Because of the robust nature of
# tcp, it will take a while before it gives up trying to establish a
-# connection. Therefore, we use select() on a non-blocking socket to
-# check against our timeout. No data bytes are actually
+# connection. Therefore, we have to set the alarm to break out of the
+# connection sooner if the timeout expires. No data bytes are actually
# sent since the successful establishment of a connection is proof
# enough of the reachability of the remote host. Also, tcp is
# expensive and doesn't need our help to add to the overhead.
my ($self,
$ip, # Packed IP number of the host
$timeout # Seconds after which ping times out
- ) = @_;
-
- my $ret;
-
- # tcp_connect won't work on win32, so special-case it if need be.
- if ($^O =~ /win32/i) {
- $ret = $self->ping_tcp_win32($ip, $timeout);
- } else {
- $ret = $self->tcp_connect($ip, $timeout);
- $self->{"fh"}->close();
- }
-
- return $ret;
-}
-
-# Description: Perform a stream ping. If the tcp connection isn't
-# already open, it opens it. It then sends some data and waits for
-# a reply. It leaves the stream open on exit.
-
-sub ping_stream
-{
- my ($self,
- $ip, # Packed IP number of the host
- $timeout # Seconds after which ping times out
) = @_;
+ my ($saddr, # sockaddr_in with port and ip
+ $ret # The return value
+ );
- my $pingstring = "ping!\n"; # The data we exchange with the server
-
- # Open the stream if it's not already open
- if(!defined $self->{"fh"}->fileno()) {
- $self->tcp_connect($ip, $timeout) or return 0;
- }
-
- croak "tried to switch servers while stream pinging"
- if $self->{"ip"} ne $ip;
-
- return $self->tcp_echo($timeout, "pingschwingping!\n");
-}
+ socket($self->{"fh"}, &PF_INET(), &SOCK_STREAM(), $self->{"proto_num"}) ||
+ croak("tcp socket error - $!");
+ $saddr = sockaddr_in($self->{"port_num"}, $ip);
-# Description: opens the stream. You would do this if you want to
-# separate the overhead of opening the stream from the first ping.
+ $SIG{'ALRM'} = sub { die };
+ alarm($timeout); # Interrupt connect() if we have to
-sub open
-{
- my ($self,
- $ip, # Packed IP number of the host
- $timeout # Seconds after which open times out
- ) = @_;
-
- $timeout = $self->{"timeout"} unless $timeout;
-
- if($self->{"proto"} eq "stream") {
- if(defined($self->{"fh"}->fileno())) {
- croak("socket is already open");
- } else {
- $self->tcp_connect($ip, $timeout);
- }
- }
+ $ret = 0; # Default to unreachable
+ eval {
+ die $! unless connect($self->{"fh"}, $saddr);
+ $ret = 1;
+ };
+ alarm(0);
+ $ret = 1 if $@ =~ /connection refused/i;
+ $self->{"fh"}->close();
+ return($ret);
}
# Description: Perform a udp echo ping. Construct a message of
elsif ($nfound) # A packet is waiting
{
$from_msg = "";
- $from_saddr = recv($self->{"fh"}, $from_msg, 1500, $flags)
- or last; # For example an unreachable host will make recv() fail.
- ($from_port, $from_ip) = sockaddr_in($from_saddr);
- if (($from_ip eq $ip) && # Does the packet check out?
- ($from_port == $self->{"port_num"}) &&
- ($from_msg eq $msg))
- {
- $ret = 1; # It's a winner
- $done = 1;
- }
- }
+ $from_saddr = recv($self->{"fh"}, $from_msg, 1500, $flags);
+ ($from_port, $from_ip) = sockaddr_in($from_saddr);
+ if (($from_ip eq $ip) && # Does the packet check out?
+ ($from_port == $self->{"port_num"}) &&
+ ($from_msg eq $msg))
+ {
+ $ret = 1; # It's a winner
+ $done = 1;
+ }
+ }
else # Oops, timed out
{
$done = 1;
}
}
return($ret);
-}
+}
# Description: Close the connection unless we are using the tcp
# protocol, since it will already be closed.
Net::Ping - check a remote host for reachability
+$Id: Ping.pm,v 1.5 2001/11/19 09:44:18 rob Exp $
+
=head1 SYNOPSIS
use Net::Ping;
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 "$host not reachable ", scalar(localtime()), "\n"
sleep(300);
}
undef($p);
-
+
# For backward compatibility
print "$host is alive.\n" if pingecho($host);
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.
-
-=over 4
-
-=item icmp
-
-The C<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.
-
-=item udp
+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.
-The C<ping()> method sends a udp
+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 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 L<inetd(8)> for
-more information.
-
-=item tcp
-
-The C<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.
-
-=item 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 C<close()> before trying to ping
-a different network device.
-
-=item external
-
-The ping() method attempts to use the C<Net::Ping::External> module to ping
-the remote host. C<Net::Ping::External> interfaces with your system's default
-L<ping(8)> utility to perform the ping, and generally produces relatively
-accurate results. If C<Net::Ping::External> if not installed on your
-system, specifying the "external" protocol will result in an error.
+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.
=head2 Functions
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.
-=item $p->open($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 C<open()>, the connection is
-automatically openeed the first time C<ping()> is called.
-This call simply does nothing if you are using any protocol other
-than stream.
-
=item $p->close();
Close the network connection for this ping object. The network
=back
+=head1 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.
+
=head1 NOTES
There will be less network overhead (and some efficiency in your
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.
+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
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.
+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.
+=head1 AUTHOR(S)
+
+ Original pingecho():
+ Andreas Karrer (karrer@bernina.ethz.ch)
+ Paul Marquess (pmarquess@bfsec.bt.co.uk)
+
+ Net::Ping base code:
+ Russell Mosemann (mose@ns.ccsn.edu)
+
+ Compatibility porting so ping_tcp()
+ can work with most remote systems:
+ Rob Brown (rob@roobik.com)
+
+=head1 COPYRIGHT
+
+Copyright (c) 2001 Rob Brown. All rights reserved.
+
+Copyright (c) 1996 Russell Mosemann. All rights reserved.
+
+This program is free software; you may redistribute it and/or
+modify it under the same terms as Perl itself.
+
=cut
--- /dev/null
+NAME
+ Net::Ping - check a remote host for reachability
+
+ $Id: Ping.pm,v 1.5 2001/11/19 09:44:18 rob Exp $
+
+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);
+ # 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()), "\n"
+ unless $p->ping($host);
+ sleep(300);
+ }
+ undef($p);
+
+ # For backward compatibility
+ print "$host is alive.\n" if pingecho($host);
+
+DESCRIPTION
+ This module contains methods to test the reachability of remote hosts on
+ a network. A ping object is first created with optional parameters, a
+ variable number of hosts may be pinged multiple times and then the
+ connection is closed.
+
+ You may choose one of three different protocols to use for the ping.
+ With the "tcp" protocol the ping() method attempts to establish a
+ connection to the remote host's echo port. If the connection is
+ successfully established, the remote host is considered reachable. No
+ data is actually echoed. This protocol does not require any special
+ privileges but has higher overhead than the other two protocols.
+
+ Specifying the "udp" protocol causes the ping() method to send a udp
+ packet to the remote host's echo port. If the echoed packet is received
+ from the remote host and the received packet contains the same data as
+ the packet that was sent, the remote host is considered reachable. This
+ protocol does not require any special privileges.
+
+ If the "icmp" protocol is specified, the ping() method sends an icmp
+ echo message to the remote host, which is what the UNIX ping program
+ does. If the echoed message is received from the remote host and the
+ echoed information is correct, the remote host is considered reachable.
+ Specifying the "icmp" protocol requires that the program be run as root
+ or that the program be setuid to root.
+
+ Functions
+
+ Net::Ping->new([$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.
+
+AUTHOR(S)
+ Original pingecho():
+ Andreas Karrer (karrer@bernina.ethz.ch)
+ Paul Marquess (pmarquess@bfsec.bt.co.uk)
+
+ Net::Ping base code:
+ Russell Mosemann (mose@ns.ccsn.edu)
+
+ Compatibility porting so ping_tcp()
+ can work with most remote systems:
+ Rob Brown (rob@roobik.com)
+
+COPYRIGHT
+ Copyright (c) 2001 Rob Brown. All rights reserved.
+
+ Copyright (c) 1996 Russell Mosemann. All rights reserved.
+
+ This program is free software; you may redistribute it and/or modify it
+ under the same terms as Perl itself.
+
projects / p5sagit/p5-mst-13.2.git / commitdiff