Windows configuration NTP server

Configure the Windows time service to use an external time source
Administrators can configure the Windows time service on the PDC operations master at the root of the forest to recognize the external Simple Network Time Protocol (SNTP) time server as an authoritative time server. For example, you can use a Microsoft time server (time.windows.com) as an external SNTP time server. To configure the Windows time service to use an external SNTP time server, follow these steps:
1. Click Start, click Run, type regedit, and then click OK.
2. Follow these steps to change the server type to NTP:
A. Locate and then click the following registry subkey:
HKEY LOCAL Machine\\system\\currentcontrolset\\services\\w32time\\parameters
B. In the right pane, right-click the TYPE, and then click Modify.
C. In edit value, type NTP in the Value data box, and then click OK.

3. Follow these steps to configure the server as a reliable time source:
A. In the right pane, right-click Reliabletimesource, and then click Modify.
B. In the edit DWORD value, type 1 in the Value data box, and then click OK.

4. Follow these steps to configure the server LOCALNTP to 1:
A. In the right pane, right-click LOCALNTP, and then click Modify.
B. In the edit DWORD value, type 1 in the Value data box, and then click OK.

5. Follow these steps to specify a time source:
A. In the right pane, right-click NtpServer, and then click Modify.
B. In edit value, type peers in the Value data box, and then click OK.

Note: Peers is a placeholder that should be replaced by a space-delimited list of peers from which your computer gets the timestamp. Each DNS name that is listed must be unique.

6. Adjust the time calibration settings (Windows 4 Service Pack only). To do this, follow these steps:
A. Locate and then click the following registry subkey:
Hkey_local_machine\\system\\currentcontrolset\\services\\w32time\\parameters
B. In the right pane, right-click MaxAllowedClockErrInSecs, and then click Modify.
C. In the edit DWORD value, type TimeInSeconds in the Value data box, and then click OK.

Note: TimeInSeconds is a placeholder and should be replaced by the number of seconds that you want each poll to take. The recommended value is 900. This value configures the time server to poll every 15 minutes.

7. Set the polling interval by following these steps:
A. Locate and then click the following registry subkey:
HKEY LOCAL Machine\\system\\currentcontrolset\\services\\w32time\\parameters
B. In the right pane, right-click Period, and then click Modify.
C. In the edit DWORD value, type 24 in the Value data box, and then click OK.

8. On the File menu, click Exit to exit Registry Editor.
9. At the command prompt, type the following command to restart the Windows time service, and then press Enter:
net stop W32Time && net start W32Time
10. Run the following command on all computers except the time server to reset the local computer's time based on the time server:
W32tm-s

By default, SNTP uses User Datagram Protocol (UDP) port 123. If this port is not open to the Internet, you cannot synchronize your server with the Internet SNTP server. A computer that is configured as a reliable time source is identified as the root of the Windows time service. The root of the time service is the authoritative server for the domain and is typically configured to retrieve time from an external NTP server or hardware device. You can configure a time server as a reliable time source to optimize the way you transfer time across the domain hierarchy. If you configure a domain controller as a reliable time source, the Net Logon service will announce it as a reliable time source when the domain controller logs on to the network. When other domain controllers look for a time source to synchronize with, they prefer the existing reliable time source.

The HKEY LOCAL machine\\system\\currentcontrolset\\services\\w32time\\parameters\\period registry key controls how often the Windows time service synchronizes. The value specified for it can only be one of the special values in the following table:
65531, "DailySpecialSkew"-set to synchronize every 45 minutes, until one succeeds, and then synchronize once a day.
65532, "Specialskew"-set to synchronize every 45 minutes until there are three successes, and then synchronize every 8 hours. This is the default setting.
65533, "Weekly"-set to synchronize every 7 days.
65534, "tridaily"-set to synchronize every 3 days.
65535, "bidaily"-set to synchronize every 2 days.
0-For NT5DS, synchronize every 45 minutes until three successes and then synchronize every 8 hours. For NTP, it is synchronized every 8 hours.
Freq-freq indicates the number of times you want the Windows time service to synchronize daily. You must use this option if you do not want to use those values that you have specified beforehand.

Windows configuration NTP server