What Is NTP?

What Is NTP? — NTP stands for Network Time Protocol. It is an Internet standard protocol (built on top of TCP/IP) that is used to synchronize the clocks of client computers. NTP sends time requests to known servers and obtains server time stamps. Using those stamps, it adjusts the client’s time.

The following are some of the features of NTP:
* It is fault tolerant and dynamically autoconfiguring.
* It synchronizes accuracy up to one millisecond.
* It can be used to synchronize all computers in a network.
* It uses UTC time.
* It is available for every type of computer.

NTP Stratum Levels

Stratum levels determine the distance from the reference clock. A reference clock is stratum-0 equipment that is considered to be accurate and has little delay. The reference clock matches its time with the correct UTC time using long-wave radio signals, GPS transmissions, CDMA technology, or other time signals, such as WWV and DCF77.

Stratum-0 servers are not directly used on the network. They are directly connected to computers that work as stratum-1 servers. Higher stratum levels are connected to stratum-1 servers over a network path; therefore, stratum-2 servers get their time from stratum-1 servers through NTP over a network link. In the same way, stratum-3 servers get their time from stratum-2 servers, and so on.

Depending on the reference clock of a stratum-1 time server, its accuracy to UTC can be within less than one millisecond (ms).

NTP Time Servers

The following tables list NTP time servers. The tables are provided as reference only. This list is not intended to be comprehensive. Any NTP time server selection should be evaluated to determine if the server in question meets specific time server requirements.

Server Name IP Address Location
time-a.nist.gov 129.6.15.28 NIST, Gaithersburg, Maryland
time-b.nist.gov 129.6.15.29 NIST, Gaithersburg, Maryland
time-a.timefreq.bldrdoc.gov 132.163.4.101 NIST, Boulder, Colorado
time-b.timefreq.bldrdoc.gov 132.163.4.102 NIST, Boulder, Colorado
time-c.timefreq.bldrdoc.gov 132.163.4.103 NIST, Boulder, Colorado
utcnist.colorado.edu 128.138.140.44 University of Colorado, Boulder
time.nist.gov 192.43.244.18 NCAR, Boulder, Colorado
time-nw.nist.gov 131.107.1.10 Microsoft, Redmond, Washington
nist1.dc.certifiedtime.com 216.200.93.8 Abovnet, Northern Virginia
nist1.datum.com 209.0.72.7 Datum, San Jose,California
nist1.nyc.certifiedtime.com 208.184.49.129 Abovnet, New York City
nist1.sjc.certifiedtime.com 207.126.103.202 Abovnet, San Jose,California

Configuring the Windows Time Service

To configure Windows time service to use an internal hardware clock, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click on the registry subkey HKEY LOCAL MACHINE\SYSTEM\CurrentControlSet\ Services\W32Time\Parameters.
3. In the right pane, right-click ReliableTimeSource, and then click Modify.
4. In Edit DWORD Value, type 1 in the Value data box, and then click OK.
5. Locate and then click on the registry subkey HKEY LOCAL MACHINE\SYSTEM\CurrentControlSet\ Services\W32Time\Parameters.
6. In the right pane, right-click LocalNTP, and then click Modify.
7. In Edit DWORD Value, type 1 in the Value data box, and then click OK.
8. Quit Registry Editor.
9. At the command prompt, run the net stop w32time && net start w32time command to restart the Windows time service.
10. “Run the w32tm -s command on all computers other than the time server to reset the local computer’s time against the time server.”

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Originally published at https://exploitbyte.com on December 30, 2020.