net::ping.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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.\" ========================================================================
.\"
.IX Title "Net::Ping 3"
.TH Net::Ping 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Net::Ping \- check a remote host for reachability
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Net::Ping;
\&
\&    $p = Net::Ping\->new();
\&    print "$host is alive.\en" if $p\->ping($host);
\&    $p\->close();
\&
\&    $p = Net::Ping\->new("icmp");
\&    $p\->bind($my_addr); # Specify source interface of pings
\&    foreach $host (@host_array)
\&    {
\&        print "$host is ";
\&        print "NOT " unless $p\->ping($host, 2);
\&        print "reachable.\en";
\&        sleep(1);
\&    }
\&    $p\->close();
\&
\&    $p = Net::Ping\->new("tcp", 2);
\&    # Try connecting to the www port instead of the echo port
\&    $p\->port_number(getservbyname("http", "tcp"));
\&    while ($stop_time > time())
\&    {
\&        print "$host not reachable ", scalar(localtime()), "\en"
\&            unless $p\->ping($host);
\&        sleep(300);
\&    }
\&    undef($p);
\&
\&    # Like tcp protocol, but with many hosts
\&    $p = Net::Ping\->new("syn");
\&    $p\->port_number(getservbyname("http", "tcp"));
\&    foreach $host (@host_array) {
\&      $p\->ping($host);
\&    }
\&    while (($host,$rtt,$ip) = $p\->ack) {
\&      print "HOST: $host [$ip] ACKed in $rtt seconds.\en";
\&    }
\&
\&    # High precision syntax (requires Time::HiRes)
\&    $p = Net::Ping\->new();
\&    $p\->hires();
\&    ($ret, $duration, $ip) = $p\->ping($host, 5.5);
\&    printf("$host [ip: $ip] is alive (packet return time: %.2f ms)\en", 1000 * $duration)
\&      if $ret;
\&    $p\->close();
\&
\&    # For backward compatibility
\&    print "$host is alive.\en" if pingecho($host);
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
You may choose one of six different protocols to use for the
ping. The \*(L"tcp\*(R" 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 \*(L"icmp\*(R" pingable.
.PP
With the \*(L"tcp\*(R" protocol the \fIping()\fR 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 \*(L"udp\*(R" and \*(L"icmp\*(R" protocols.
.PP
Specifying the \*(L"udp\*(R" protocol causes the \fIping()\fR 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 a udp ping, a host
will be reported as unreachable if it is not running the
appropriate echo service.  For Unix-like systems see \fIinetd\fR\|(8)
for more information.
.PP
If the \*(L"icmp\*(R" protocol is specified, the \fIping()\fR method sends an icmp
echo message to the remote host, which is what the \s-1UNIX\s0 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 \*(L"icmp\*(R" protocol requires that the program
be run as root or that the program be setuid to root.
.PP
If the \*(L"external\*(R" protocol is specified, the \fIping()\fR method attempts to
use the \f(CW\*(C`Net::Ping::External\*(C'\fR module to ping the remote host.
\&\f(CW\*(C`Net::Ping::External\*(C'\fR interfaces with your system's default \f(CW\*(C`ping\*(C'\fR
utility to perform the ping, and generally produces relatively
accurate results. If \f(CW\*(C`Net::Ping::External\*(C'\fR if not installed on your
system, specifying the \*(L"external\*(R" protocol will result in an error.
.PP
If the \*(L"syn\*(R" protocol is specified, the \fIping()\fR method will only
send a \s-1TCP\s0 \s-1SYN\s0 packet to the remote host then immediately return.
If the syn packet was sent successfully, it will return a true value,
otherwise it will return false.  \s-1NOTE:\s0 Unlike the other protocols,
the return value does \s-1NOT\s0 determine if the remote host is alive or
not since the full \s-1TCP\s0 three-way handshake may not have completed
yet.  The remote host is only considered reachable if it receives
a \s-1TCP\s0 \s-1ACK\s0 within the timeout specified.  To begin waiting for the
\&\s-1ACK\s0 packets, use the \fIack()\fR method as explained below.  Use the
\&\*(L"syn\*(R" protocol instead the \*(L"tcp\*(R" protocol to determine reachability
of multiple destinations simultaneously by sending parallel \s-1TCP\s0
\&\s-1SYN\s0 packets.  It will not block while testing each remote host.
demo/fping is provided in this distribution to demonstrate the
\&\*(L"syn\*(R" protocol as an example.
This protocol does not require any special privileges.
.Sh "Functions"
.IX Subsection "Functions"
.ie n .IP "Net::Ping\->new([$proto [, $def_timeout\fR [, \f(CW$bytes\fR [, \f(CW$device\fR [, \f(CW$tos ]]]]]);" 4
.el .IP "Net::Ping\->new([$proto [, \f(CW$def_timeout\fR [, \f(CW$bytes\fR [, \f(CW$device\fR [, \f(CW$tos\fR ]]]]]);" 4
.IX Item "Net::Ping->new([$proto [, $def_timeout [, $bytes [, $device [, $tos ]]]]]);"
Create a new ping object.  All of the parameters are optional.  \f(CW$proto\fR
specifies the protocol to use when doing a ping.  The current choices
are \*(L"tcp\*(R", \*(L"udp\*(R", \*(L"icmp\*(R", \*(L"stream\*(R", \*(L"syn\*(R", or \*(L"external\*(R".
The default is \*(L"tcp\*(R".
.Sp
If a default timeout ($def_timeout) in seconds is provided, it is used
when a timeout is not given to the \fIping()\fR method (below).  The timeout
must be greater than 0 and the default, if not specified, is 5 seconds.
.Sp