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Windows Time Server: Synchronising Your Network With Ntp

Nearly all a computers activity involves time whether logging a timestamp for when a network was accessed to sending an email, knowing the time is crucial for computer applications.

All computers have an on-board clock that provides time and date information. These Real Time Clock (RTC) chips are battery backed so that even when off they can maintain time, however these RTC chips are mass produced and cannot maintain accurate time and tend to drift.

For many applications this can be quite adequate, however if a computer is on a network and needs to talk to other machines, failing to be synchonised to the correct time can mean many time-sensitive transactions can not be completed and can even leave the network open to security threats.

All versions of Windows Server since 2000 have included a time synchronization facility, called Windows Time Service (w32time.exe), built into the operating system. This can be configured to operate as a network time server synchronizing all machines to a specific time source.

Windows Time Service uses a version of NTP (Network Time Protocol), normally a simplified version, of the Internet protocol which is designed to synchronise machines on a network, NTP is also the standard for which most computer networks across the global use to synchronise with.

Choosing the correct time source is vitally important. Most networks are synchronized to UTC (Coordinated Universal Time) source. UTC is a global standardized time based on atomic clocks which are the most accurate time sources.

UTC can be obtained over the Internet from such places as time.nist.gov (us Naval Observatory) or time.windows.com (Microsoft) but it must be noted that internet time sources can not be authenticated which can leave a system open to abuse and Microsoft and others advise using an external hardware source as a reference clock such as a specialized NTP server.

NTP servers receive their time source from either a specialist radio transmission from national physics laboratories which broadcast UTC time taken from an atomic clock source or by the GPS network which also relays UTC as a consequence of needing it to pin point locations.

NTP can maintain time over the public Internet to within 1/100th of a second (10 milliseconds) and can perform even better over LANs.

To configure Windows Time Service to use an external time source simply follow these instructions.

Locate the registry subkey.

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters

Right click type then Modify the Value by inserting NTP in the Value Data box.

Right click ReliableTimeSource, then Modify the Edit DWORD Value box, by inserting 0 (zero).

Right-click NtpServer then Modify the Edit Value by typing the Domain Name System (DNS), (note each DNS must be unique).

Now locate the original subkey and right-click Period Modify the Edit DWORD Value box with the poll interval (how often a NTP server polls the time), under Value Data (recommended 24)

Run the following command line, Net stop w32time && net start w32time.

Now enable NTP by locating the subkey, HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpServer

Right click Enabled and modify the Value data box by typing 1.

Right Click SpecialPollInterval in the right pain of the subkey HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpClientSpecialPollInterval. Edit the DWORD value box the time you want for each poll (900 will poll every 15 minutes)

Locate HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig

To configure the time correction settings right click MaxPosPhaseCorrection, then modify the DWORD Value box with a time in seconds such (select decimal under base first, 3600 = one hour)

Now do the same for MaxNegPhaseCorrection the restart windows time service by running (or alternatively use the command prompt facility) net stop w32time && net start w32time.

To synchronise each machine simply type W32tm/ -s in the command prompt and the time server should now be working correctly (note it may take several polls before the correct time is displayed).

 

 

 

 

 

 

 

 

 

About the Author

Richard N Williams is a technical author and a specialist in the telecommunications and network time synchronisation industry helping to develop dedicated NTP clocks. Please visit us for more information about NTP or other network time server solutions.

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Configuring a Windows Based Ntp Network Time Server

 

Computer time synchronisation is highly important in modern computer networks, precision and time synchronization is critical in many applications, particularly time sensitive transactions. Just imagine buying an airline seat only to be told at the airport that the ticket was sold twice because it was purchased afterwards on a computer that had a slower clock!

Modern computers do have internal clocks called Real Time Clock chips (RTC) that provide time and date information. These chips are battery backed so that even during power outages, they can maintain time but personal computers are not designed to be perfect clocks. Their design has been optimized for mass production and low-cost rather than maintaining accurate time.

For many applications, this is can be quite adequate, although, quite often machines need time to be synchronised with other PC's on a network and when computers are out of sync with each other problems can arise such as sharing network files or in some environments even fraud!

Microsoft Windows (2000 and above) has a time synchronisation utility built into the operating system called Windows Time (w32time.exe) which can be configured to operate as a network time server. It can be configured to both synchronise a network using the internal clock or an external time source.

Note: Microsoft strongly recommends that you configure a time server with a hardware source rather than from the internet where there is no authentication.

To configure Windows Time service to use the internal hardware clock, first check that w32time is located in the system services list in the registry, to check:

Click Start, Run then type regedit then click ok.

Locate and then click the following registry entry:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Time

It is highly recommended that you back up the registry as serious problems may occur if you modify the registry incorrectly, modifications to the registry are done at your own risk.

Note: the following instructions are based on Windows 2000 other versions of Windows may differ.

To begin configuration for an internal clock, click on the following subkey:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters

In the right pane, right-click ReliableTimeSource, then click Modify.

In Edit DWORD Value, type 1 in the Value Data box, then click OK

Exit Registry Editor

To restart the Windows Time Service click Start, Run (or alternatively use the Command Prompt facility).

Type: net stop w32time && net start w32time

Then press enter.

To reset the local computers’ time, type the following on all computers except for the time server which must not be synchronised with itself:

w32tm –s

To configure the Windows Time service to use an external time source, click Start, Run and type regedit then click OK.

Locate the following subkey:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters

In the right pane, right-click Type then click Modify, in edit Value type NTP in the Value data box then click OK.

Now in the right pane, right click ReliableTimeSource, then click Modify.

In the Edit DWORD Value box, under Value Data, type 0, then click OK.

Right-click NtpServer in the right pane then click Modify.

In Edit Value, type the Domain Name System (DNS), each DNS must be unique.

Now click Ok.

For Windows 2000 Service Pack 4 only, set the time correction settings to do this locate:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters

In the right pane, right-click MaxAllowedClockErrInSecs, then Modify in the Edit DWORD Value box, , type a time in seconds max number of seconds difference between the local clock and the time received from the NTP server in order to be considered a valid new time.

Click OK.

To set the poll intervals locate:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters

In the right pane, right-click Period, then click Modify.

In the Edit DWORD Value box, under Value Data, type 24 then OK

Exit Registry Editor

Click Start, then Run then type the following and press Enter:

Net stop w32time && net start w32time

To reset the local computers’ time, type the following on all computers except for the time server which must not be synchronised with itself:

Network Time Protocol (NTP) is an Internet protocol used for the transfer of accurate time, providing time information along so that a precise time can be obtained

To enable the Network Time Protocol; NTPserver, locate and click:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpServer

In the right pane, right-click Enabled, then click Modify.

In the Edit DWord Value box, type 1 under Value data, then click OK.

Now go back and click on

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParametersNtpServer

In the right pane, right-click NtpServer, then Modify, in the Edit DWORD Value under Value Data type In the right pane, right-click NtpServer, then Modify, in the Edit DWORD Value under Value Data type the Domain Name System (DNS), each DNS must be unique and you must append 0x1 to the end of each DNS name otherwise changes will not take effect.

Now click Ok.

Locate and click the following

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpClientSpecialPollInterval

In the right pane, right-click SpecialPollInterval, then click Modify.

In the Edit DWORD Value box, under Value Data, type the number of seconds you want for each poll, ie 900 will poll every 15 minutes, then click OK.

To configure the time correction settings, locate:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig

In the right pane, right-click MaxPosPhaseCorrection, then Modify, in the Edit DWORD Value box, under Base, click Decimal, under Value Data, type a time in seconds such as 3600 (an hour) then click OK.

Now go back and click:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32Timeconfig

In the right pane, right-click MaxNegPhaseCorrection, then Modify.

In the Edit DWORD box under base, click Decimal, under value data type the time in seconds you want to poll such as 3600 (polls in one hour)

Exit Registry Editor

Now to restart windows time service, click Start, Run (or alternatively use the command prompt facility) and type:

net stop w32time && net start w32time

And on each computer, other than the time server, type:

W32tm/ -s

And that’s it your time server should be now up and running.

About the Author

Richard N Williams is a technical author and a specialist in the telecommunications and network time synchronisation industry helping to develop dedicated time server products. Please visit us for more information about a GPS time server or other NTP server products.

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