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SNTP date and time (UTC) from an NTP time server
#!/usr/bin/perl -w
#
# sntp.pl
#
my $PgmName = "SNTP - Get time from an NTP time server";
my $VERSION = "0.2b, 2004-12-10";
#
=head1 SNTP - Get time from an NTP time server
This program has been written just for fun to take a short look on the NTP stuff
and to learn about the NTP/SNTP data :
get time information from an NTP time server using SNTP (Simple Network Time
Protocol, RFC-2030), analyze the protocol information, and display what we've got.
Finally optionally set the local unix system clock, if you wish.
For real time synchronization, please use a more professional client software.
(c) 2001, Ralf D. Kloth <ralf at kloth.net | ralf at qrq.de>, QRQ.software.
All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself
(Perl Artistic License, http://dev.perl.org/licenses/artistic.html).
THIS PRGOGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESSED OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
You are using this program at own risk.
Written and tested under Perl V 5.6.0 on Linux 2.4.
Revision history:
V0.1, 2000-09-30, first version
V0.2, 2001-03-31, published version
V0.2b, 2004-12-10, minor patch by Tim Braun
usage: perl sntp.pl [-u (update the unix clock)] <timeserver>
Attention: Year-2036 problem:
This program will not work after the NTP timestamp rollover on 2036-02-07.
Finally, RFC-2030 recommends the following on stratum usage:
As the load on the hosts supporting NTP primary (stratum 1) time service is heavy
and always increasing, clients should avoid using the primary servers whenever
possible. In most cases the accuracy of the NTP secondary (stratum 2) servers is
only slightly degraded relative to the primary servers and, as a group, the
secondary servers may be just as reliable.
List of stratum 2 servers: http://www.eecis.udel.edu/~mills/ntp/clock2.htm
=cut
use strict;
use IO::Socket;
use Time::HiRes qw(time);
use Getopt::Std;
sub usage { # print a short 'usage` message and exit
print "usage: perl $0 <timeserver>\n";
print " [-u (update the unix clock)]\n";
exit;
}
use vars qw($opt_h $opt_u); # command line options
print "$0, $PgmName, V $VERSION \n";
# handle the commandline options
getopts('hu'); # look for -h and -u
$opt_h && usage; # -h print usage message and exit
(!$ARGV[0]) && usage; # no server: print usage message and exit
my $server = $ARGV[0];
my $serverIPv4 ="";
if (gethostbyname($server)) {
$serverIPv4 = sprintf("%d.%d.%d.%d",unpack("C4",gethostbyname($server)));
}
my $timeout = 2;
sub bin2frac { # convert a binary string to fraction
my @bin = split '', shift;
my $frac = 0;
while (@bin) {
$frac = ($frac + pop @bin)/2;
}
$frac;
} # end sub bin2frac
sub frac2bin { # convert a fraction to binary string (B32)
my $frac = shift;
my $bin ="";
while (length($bin) < 32) {
$bin = $bin . int($frac*2);
$frac = $frac*2 - int($frac*2);
}
$bin;
} # end sub frac2bin
my ($LocalTime0, $LocalTime0F, $LocalTime0H, $LocalTime0FH, $LocalTime0FB);
my ($LocalTime1, $LocalTime2);
my ($LocalTime, $LocalTimeF, $LocalTimeT);
my ($NetTime, $NetTime2, $Netfraction);
my ($netround, $netdelay, $off);
my ($Byte1, $Stratum, $Poll, $Precision,
$RootDelay, $RootDelayFB, $RootDisp, $RootDispFB, $ReferenceIdent,
$ReferenceTime, $ReferenceTimeFB, $OriginateTime, $OriginateTimeFB,
$ReceiveTime, $ReceiveTimeFB, $TransmitTime, $TransmitTimeFB);
my ($dummy, $RootDelayH, $RootDelayFH, $RootDispH, $RootDispFH, $ReferenceIdentT,
$ReferenceTimeH, $ReferenceTimeFH, $OriginateTimeH, $OriginateTimeFH,
$ReceiveTimeH, $ReceiveTimeFH, $TransmitTimeH, $TransmitTimeFH);
my ($LI, $VN, $Mode, $sc, $PollT, $PrecisionV, $ReferenceT, $ReferenceIPv4);
my $ntp_msg; # NTP message according to NTP/SNTP protocol specification
sub get_ntp_time {
# open the connection to the ntp server,
# prepare the ntp request packet
# send and receive
# take local timestamps before and after
my ($remote);
my ($rin, $rout, $eout) ="";
my $ntp_msg;
# open the connection to the ntp server
$remote = IO::Socket::INET -> new(Proto => "udp", PeerAddr => $server,
PeerPort => 123,
Timeout => $timeout)
or die "Can't connect to \"$server\"\n";
# measure local time BEFORE timeserver query
$LocalTime1 = time();
# convert fm unix epoch time to NTP timestamp
$LocalTime0 = $LocalTime1 + 2208988800;
# prepare local timestamp for transmission in our request packet
$LocalTime0F = $LocalTime0 - int($LocalTime0);
$LocalTime0FB = frac2bin($LocalTime0F);
$LocalTime0H = unpack("H8",(pack("N", int($LocalTime0))));
$LocalTime0FH = unpack("H8",(pack("B32", $LocalTime0FB)));
$ntp_msg = pack("B8 C3 N10 B32", '00011011', (0)x12, int($LocalTime0), $LocalTime0FB);
# LI=0, VN=3, Mode=3 (client), remainder msg is 12 nulls
# and the local TxTimestamp derived from $LocalTime1
# send the ntp-request to the server
$remote -> send($ntp_msg) or return undef;
vec($rin, fileno($remote), 1) = 1;
select($rout=$rin, undef, $eout=$rin, $timeout)
or do {print "No answer from $server\n"; exit};
# receive the ntp-message from the server
$remote -> recv($ntp_msg, length($ntp_msg))
or do {print "Receive error from $server ($!)\n"; exit};
# measure local time AFTER timeserver query
$LocalTime2 = time();
$ntp_msg;
} # end sub get_ntp_time
sub interpret_ntp_data {
# do some interpretations of the data
my $ntp_msg = shift;
# unpack the received ntp-message into long integer and binary values
( $Byte1, $Stratum, $Poll, $Precision,
$RootDelay, $RootDelayFB, $RootDisp, $RootDispFB, $ReferenceIdent,
$ReferenceTime, $ReferenceTimeFB, $OriginateTime, $OriginateTimeFB,
$ReceiveTime, $ReceiveTimeFB, $TransmitTime, $TransmitTimeFB) =
unpack ("a C3 n B16 n B16 H8 N B32 N B32 N B32 N B32", $ntp_msg);
# again unpack the received ntp-message into hex and ASCII values
( $dummy, $dummy, $dummy, $dummy,
$RootDelayH, $RootDelayFH, $RootDispH, $RootDispFH, $ReferenceIdentT,
$ReferenceTimeH, $ReferenceTimeFH, $OriginateTimeH, $OriginateTimeFH,
$ReceiveTimeH, $ReceiveTimeFH, $TransmitTimeH, $TransmitTimeFH) =
unpack ("a C3 H4 H4 H4 H4 a4 H8 H8 H8 H8 H8 H8 H8 H8", $ntp_msg);
$LI = unpack("C", $Byte1 & "\xC0") >> 6;
$VN = unpack("C", $Byte1 & "\x38") >> 3;
$Mode = unpack("C", $Byte1 & "\x07");
if ($Stratum < 2) {$sc = $Stratum;}
else {
if ($Stratum > 1) {
if ($Stratum < 16) {$sc = 2;} else {$sc = 16;}
}
}
$PollT = 2**($Poll);
if ($Precision > 127) {$Precision = $Precision - 255;}
$PrecisionV = sprintf("%1.4e",2**$Precision);
$RootDelay += bin2frac($RootDelayFB);
$RootDelay = sprintf("%.4f", $RootDelay);
$RootDisp += bin2frac($RootDispFB);
$RootDisp = sprintf("%.4f", $RootDisp);
$ReferenceT = "";
if ($Stratum eq 1) {$ReferenceT = "[$ReferenceIdentT]";}
else {
if ($Stratum eq 2) {
if ($VN eq 3) {
$ReferenceIPv4 = sprintf("%d.%d.%d.%d",unpack("C4",$ReferenceIdentT));
$ReferenceT = "[32bit IPv4 address $ReferenceIPv4 of the ref src]";
}
else {
if ($VN eq 4) {$ReferenceT = "[low 32bits of latest TX timestamp of reference src]";}
}
}
}
$ReferenceTime += bin2frac($ReferenceTimeFB);
$OriginateTime += bin2frac($OriginateTimeFB);
$ReceiveTime += bin2frac($ReceiveTimeFB);
$TransmitTime += bin2frac($TransmitTimeFB);
} # end sub interpret_ntp_data
sub calculate_time_data {
# convert time stamps to unix epoch and do some calculations on the time data
my ($sec, $min, $hr, $dy, $mo, $yr);
$ReferenceTime -= 2208988800; # convert to unix epoch time stamp
$OriginateTime -= 2208988800;
$ReceiveTime -= 2208988800;
$TransmitTime -= 2208988800;
$NetTime = scalar(gmtime $TransmitTime);
$Netfraction = sprintf("%03.f",1000*sprintf("%.3f", $TransmitTime - int($TransmitTime)));
($sec, $min, $hr, $dy, $mo, $yr) = gmtime($TransmitTime);
$NetTime2 = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $yr+1900, $mo+1, $dy, $hr, $min, $sec);
# calculate delay and difference
$netround = sprintf("%+.4f",($LocalTime1 - $LocalTime2));
$netdelay = sprintf("%+.4f",(($LocalTime1 - $LocalTime2)/2) - ($TransmitTime - $ReceiveTime));
$off = sprintf("%+.4f",(($ReceiveTime - $LocalTime1) + ($TransmitTime - $LocalTime2))/2);
$LocalTime = ($LocalTime1 + $LocalTime2) /2;
$LocalTimeF = sprintf("%03.f",1000*sprintf("%.3f", $LocalTime - int($LocalTime)));
($sec, $min, $hr, $dy, $mo, $yr) = gmtime($LocalTime);
$LocalTimeT = sprintf("%04d-%02d-%02d %02d:%02d:%02d", $yr+1900, $mo+1, $dy, $hr, $min, $sec);
} # end sub calculate_time_data
sub output_ntp_data { # raw data from $ntp_msg
# output the information we have
my %LItext = ( "0" => "no warning",
"1" => "last minute of current day has 61 sec",
"2" => "last minute of current day has 59 sec",
"3" => "alarm condition (clock not synchronized)",
);
my %Modetext = ("0" => "reserved",
"1" => "symmetric active",
"2" => "symmetric passive",
"3" => "client",
"4" => "server",
"5" => "broadcast",
"6" => "reserved for NTP control message",
"7" => "reserved for private use",
);
my %Stratumtext = (
"0" => "unspecified or unavailable",
"1" => "primary reference (e.g. radio clock)",
"2" => "2...15: secondary reference (via NTP or SNTP)",
"16" => "16...255: reserved",
);
print "Local Transmit Timestp : " . $LocalTime0 . "\n";
print "The ntp server [$server $serverIPv4] sent the following data:\n";
print "Byte1 : " . ord($Byte1) . "\n";
print " Leap Indicator (LI) : $LI [" . $LItext{$LI} . "]\n";
print " Version number (VN) : $VN [NTP/SNTP version number]\n";
print " Mode : $Mode [" . $Modetext{$Mode} . "]\n";
print "Stratum : $Stratum [" . $Stratumtext{$sc} . "]\n";
print "Poll Interval : $Poll [2**$Poll = $PollT sec max interval between successive msgs]\n";
print "Clock Precision : $Precision [2**$Precision = $PrecisionV]\n";
print "Root Delay : $RootDelayH$RootDelayFH [$RootDelay sec]\n";
print "Root Dispersion : $RootDispH$RootDispFH [$RootDisp sec]\n";
print "Reference Identifier : $ReferenceIdent $ReferenceT \n";
print "Reference Timestamp : $ReferenceTimeH.$ReferenceTimeFH [" .
sprintf("%10.5f",$ReferenceTime) . "]\n";
print "Originate Timestamp : $OriginateTimeH.$OriginateTimeFH [" .
sprintf("%10.5f",$OriginateTime) . "]\n";
print "Receive Timestamp : $ReceiveTimeH.$ReceiveTimeFH [" .
sprintf("%10.5f",$ReceiveTime) . "]\n";
print "Transmit Timestamp : $TransmitTimeH.$TransmitTimeFH [" .
sprintf("%10.5f",$TransmitTime) . "]\n";
print "\n";
} # end sub output_ntp_date
sub output_ntp_data2 { # interpreted time data
# output the information we have
print "Interpreted results, converted to unix epoch (sec since 1970-01-01 00:00:00):\n";
print "Reference Timestamp : " . sprintf("%10.5f",$ReferenceTime) .
" [last sync of server clock with ref]\n";
print "Originate Timestamp : " . sprintf("%10.5f",$OriginateTime) .
" [returned Local Transmit Timestamp]\n";
print "Receive Timestamp : " . sprintf("%10.5f",$ReceiveTime) .
" [request packet arrived at server]\n";
print "Transmit Timestamp : " . sprintf("%10.5f",$TransmitTime) .
" [this reply departed the server]\n";
print "Net time UTC : $NetTime +$Netfraction ms\n";
print " $NetTime2.$Netfraction\n";
# delay and difference
print "Network roundtrip time : $netround sec";
if (abs($netround) > 1) {print " <-- high roundtrip time, try another server closer to you";}
print "\n";
print "Network delay : $netdelay sec";
if (abs($netdelay) > 1) {print " <-- high delay time, try another server closer to you";}
print "\n";
print "Local Timestamp : $LocalTime \n";
print "Local time UTC : $LocalTimeT.$LocalTimeF\n";
} # end sub output_ntp_data2
sub correct_localclock {
# set the unix clock to the nearest second
my $off = shift;
$off = sprintf("%.f", $off);
print "\nSet local system clock: ";
system("date --set=\'$off seconds\'");
} # end sub correct_localclock
# main *********************************************************************
print "Connecting to $server\n";
$ntp_msg = get_ntp_time;
interpret_ntp_data($ntp_msg);
# Check if the received packet is the correct reply to our request:
# it is correct, if our original transmit time we sent in the Transmit Time field
# of our request packet shows up in the Originate Time field of the received reply.
if (($LocalTime0H . $LocalTime0FH) ne ($OriginateTimeH . $OriginateTimeFH)) {
print "*** The received reply seems to be faulty and NOT the reply to our request packet:\n";
print "*** The OriginateTime stamp $OriginateTimeH.$OriginateTimeFH of the received packet does not \n";
print "*** show our Transmit Time $LocalTime0H.$LocalTime0FH.\n";
exit;
}
# comment this one out, if you don't want to see these data
output_ntp_data; # raw data from $ntp_msg
calculate_time_data;
# comment this one out, if you don't want to see these data
output_ntp_data2; # interpreted and calculated time data
# the final result: the difference report
print "Clock Difference : $off sec off between $server and local";
if (abs($off) > 11000) {print " <-- check this !";}
print "\n";
# if this program is executed with system privileges under unix,
# the unix clock may now be set to the nearest second
$opt_u && correct_localclock($off);
__END__
See this code working on a query to a timeserver out of the pool.ntp.org pool.
See RFC-2030 for details about the SNTP protocol.
If you have comments, or if you just found this item useful,
please drop me a line.
Your feedback is highly appreciated.
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