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<p><b><font size="4" color="green" face="Arial">Network Time Protocol (NTP)</font></b></p>
<p><font face="Arial, Helvetica, sans-serif">NTP is a protocol used to synchronize 
  time between devices.&nbsp; NTP uses UDP port 123 for communication.</font></p>
<p><font face="Arial, Helvetica, sans-serif">An NTP stratum 1 source, has an atomic 
  or radio clock directly attached.&nbsp; Startum 2 sources get their info from 
  stratum 1 sources and so on.&nbsp; Cisco routers can be configured as stratum 
  1 source without being connected to a clock.&nbsp;&nbsp;</font></p>
<p><font face="Arial, Helvetica, sans-serif">An <b>NTP master</b> is a stratum 
  1 source and provides times.&nbsp; NTP master should use the <font face="Arial, Helvetica, sans-serif"><font size="2" face="Terminal">clock 
  se</font></font><font size="2" face="Terminal">t</font> to set the router time.&nbsp; A router 
  configured with the <b>NTP peer</b> command is willing to synchronize its time 
  to the remote device or have the remote device synchronize with it.&nbsp; A 
  router configured with the <b>NTP server</b> command&nbsp; will synchronize 
  its time to the remote NTP device.</font></p>
<p><font face="Arial, Helvetica, sans-serif">NTP authentication ensures that the 
  other source is valid.&nbsp; NTP authentication uses message digest 5 encryption.</font></p>
<p><font face="Arial, Helvetica, sans-serif"><b><font size="4" color="#008000">Configuration:</font></b></font></p>
<p><font face="Times New Roman">-Router A-<br>
</font></font><font face="Terminal" size="2">Ra#clock set 16:00:00 January 30 2000<br>
Ra#conf t<br>
Ra(config)#ntp master 1<br>
Ra(config)#end<br>
Ra#</font></p>
<font face="Arial, Helvetica">
<p><font face="Times New Roman">-Router B-<br>
  </font><font face="Terminal" size="2">Rbr#conf t<br>
Rb(config)#ntp server 1.1.1.1<br>
Rb(config-if)#end<br>
Rb#&nbsp;</font></p>
<font face="Arial, Helvetica">
<p><font face="Arial, Helvetica, sans-serif">Wait a few minutes, then check the 
  status (you are looking for the word 'synchronized')</font></p>
<p><font face="Terminal" size="2">Rb#show ntp status<br>
Clock is <font color="#ff0000">synchronized</font>, stratum 2, reference is 
1.1.1.1<br>
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**19<br>
reference time is BC3EDF16.D9C4EAB8 (16:02:30.850 UTC Sun Jan 30 2000)<br>
clock offset is 0.22 msec, root delay is 30.85 msec<br>
root dispersion is 0.29 msec, peer dispersion is 0.03 msec<br>
Rb#</font></p>
<p><font face="Arial, Helvetica, sans-serif">You can also check your&nbsp; NTP 
  associations and check for synchronization there.</font></p>
<p><font face="Terminal" size="2">Rb#show ntp associations<br>
<br>
address ref clock st when poll reach delay offset disp<br>
*~1.1.1.1 .LOCL. 1 15 64 377 30.9 1.02 0.7<br>
* master (synced), # master (unsynced), + selected, - candidate, ~ configured<br>
Rb#</font></p>
<p><font face="Arial, Helvetica, sans-serif">Authentication is easy to add to 
  these configurations:</font></p>
<p><font face="Terminal" size="2">Ra(config)#ntp authenticate<br>
Ra(config)#ntp authentication-key 1 md5 snoopy<br>
Ra(config)#ntp trusted-key 1<b>&nbsp;<br>
<br>
</b>Rb(config)#ntp authenticate<br>
Rb(config)#ntp authentication-key 1 md5 snoopy<br>
  Rb(config)#ntp trusted-key 1<b>&nbsp;</b></font><font face="Times New Roman"><br>
&nbsp;</p>
<font face="Arial, Helvetica"> 
<p><font face="Arial, Helvetica, sans-serif">These are the fundamental commands 
  for configuring NTP.</font></p>
<p><font face="Arial, Helvetica, sans-serif"><b><font size="4" color="#008000">NTP 
  Lab Tricks</font></b></font></p>
<p><font face="Arial, Helvetica, sans-serif">Set the clock on both routers to 
  about the same time to begin with, NTP will synchronize faster this way.</font></p>
</font> 
<p><font size="2" face="Times New Roman, Times, serif"><span class="724482219-24092001">Copyright 
  (c) 1998-2003 Boson Software, Inc.&nbsp; All Rights Reserved.</span></font></p>

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