Network Time Protocol Notes


Single reference

  • Only time source for entire network.
  • Only one can exist on the network.
  • Adequate if 30 or less servers.


  • Takes time from at least one time provider.
  • Synchronizes its time to that of the providers.
  • Provides time information to workstations & clients.


  • Central point to set network time.
  • Primary servers adjust their internal clocks to synchronize with reference time server.
  • Gets its time information from an external source, such as an atomic clock.
  • Normally only one exists on a network, along with 3 or more primary servers.
  • Normally only used if more than 30 servers.


  • Synchronizes network time with at least 1 other primary or reference server.
  • Provides time to secondary servers, workstations & clients.
  • Normally 3-15 primary time servers per reference server.


TIMESYNC is becoming more NTP aware. In future TIMESYNC will convert completely to pure NTP.

An NTP time source that is more than 1000 seconds (about 17 minutes) different from local clock is rejected as insane.

Windows, Linux and Solaris use NTP because it is a standard time protocol.

NTP Is part of the UDP protocol suite.

NTP uses the stratum time structure, where stratum 1 is the first (highest) level in the hierarchy (usually very accurate).

NTP synchronizes to Universal Time Coordinated (UTC), the international time standard.

NTP uses port 123

The Reference-Primary-Secondary model is also known as coupled time synchronization. These servers form the time provider group. In this model time is adjusted gradually.

A pure NTP solution is known as uncoupled, when NTP sources are used exclusively. In this model an average is taken of time sources. No voting process is used. This model required TIMESYNC.NLM version 5.23o or greater.

In mixed networks you need to use NTP.

Netware Time Service (TIMESYNC)

To configure Netware to obtain time from an NTP time source configure the following parameter in MONITOR or NetWare Remote Manager:


Windows Time Service (W32Time)

In pure Windows environment clients receive time from authenticating Domain Controller (DC), which gets its time from the Primary DC (PDC).

Set time source via:

net time /setsntp:servername or IP address

or to use configured lists:

net time /setsntp:”servername1 servername2 servername3

Stop the W32 Time service:

net stop w32time

Set the Windows 2000 server time to that of the source:

w32tm –once

Start the W32 Time service:

net start w32time

Linux NTP Daemon (ntpd)

Uses the ntp.conf configuration file located in:


Below the line “Fudge” you enter:

server ip_address

Comment out the following:


Save file.
One time up-date of the time server via:

ntpdate ip_address

Start the NTP daemon with:

            /etc/rc.d/init.d/ntpd start

Or on some versions you enter /etc/rc.d/init.d/xntpd start

In order to set this to start on subsequent boots:

            chkconfig –level 3 xtntpd on
chkconfig –level 5 xtntpd on

To see the configured time sources:

            ntpq -p


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