Windows Time synchronization settings

Windows Time synchronization settings

Sometimes when our local computer is out of time, we can use the Network Time Protocol NTP (Network time protocal) to synchronize with the external time server or Windows domain server to correct the local time. Double-click the time area of the right corner to eject the Time Setting Settings dialog box (when the computer joins the domain, the time Synchronization tab is hidden), as shown in the following figure:

time synchronization server and synchronization interval adjustment

On the interface of time synchronization, we can only select under a given time synchronization server, and we cannot specify the interval of synchronization time. Let's drill down to this aspect, by adjusting the contents of the registry, to increase the number of time synchronization servers, and to adjust the time synchronization interval purposes:

To increase the time synchronization server:

Hkey_local_machine\software\microsoft\windows\currentversion\datetime\servers

Add a numeric value, the type is a string, the name is a normal number, and the value is the name of the synchronization server

To adjust the sync interval:

Hkey_local_machine\system\controlset001\services\w32time\timeproviders\ntpclient

Specialpollinterval:reg_dword sync interval value (in seconds, default value is 604800, default is 7-day sync)

Time Synchronization Protocol

Network Time Protocol (NTP) is a protocol used to synchronize computer times, enabling computers to synchronize their servers or clock sources (such as GPS sync clocks, GPS time servers, and so on). The NTP was proposed in 1985 by Professor David L. Mills of the University of the United States, in addition to estimating the round-trip latency of packets on the network, and independently estimating the computer clock bias to achieve high precision computer school on the network, It is a communication protocol designed to enable different machines to maintain the same time on the Internet. A time server is a server that uses NTP to keep the machines in the network synchronized over time. In most places, NTP can provide a reliable 1-50ms synchronization time source and network working path.

How NTP works
NTP provides accurate time, first of all to have an accurate time source, this time should be international standard UTC. NTP can obtain UTC in time from atomic clocks, observatories, satellites, or from the Internet. This will have an accurate and reliable time source. Time is propagated at the level of the NTP server. All servers are grouped into different stratun (layers) According to the distance from the external UTC source. Stratum-1 at the top, with external UTC access, while Stratum-2 gets time from Stratum-1, Stratum-3 gets time from Stratum-2, and so on, but the total number of stratum layers is limited to 15. All of these servers logically form a ladder-type architecture that is interconnected, while the Stratum-1 time server is the foundation of the entire system. Computer host is usually connected with multiple time servers, using statistical algorithms to filter the time from different servers to select the best path and source to correct the host time. The NTP service works even if the host is unable to connect with a time server for a long time. To prevent malicious damage to the time server, NTP used the identification (authentication) mechanism to check whether the information from the right time was actually coming from the declared server and checking the return path of the data to provide protection against interference.

Implementation of network-time Protocol (NTP)
The time server can take advantage of the following three ways to pair with other servers: Broadcast/multicastclient/serversymmetricbroadcast/multicast mode is mainly applicable to LAN environment, The time server periodically broadcasts, sending time information to the time servers in other networks, with only a little latency and a very simple configuration. However, the accuracy of this method is not high, the time accuracy requirements are not very high in the case can be used. Symmetric way to get a server can get the clock from the remote time server, if necessary can also provide time information to the remote time server. This approach is suitable for configuring a redundant time server and can provide higher precision to the host. The client/server approach is similar to the symmetric approach, except that it is not available for other time server time information, which is suitable for a time server to receive the time information of the upper-level time server and to provide time information to the lower level users. In all three of these ways, the transmission of time information uses the UDP protocol. Each time package contains the time information for the most recent event, including the time when the last event was sent and received, the local time that the current event was delivered, and the time the packet was received. After receiving the above package, we can calculate the amount of time and the time delay of transferring the data. The time server uses a filtering algorithm, and the previous eight school time data to calculate the time reference value, to determine the accuracy of subsequent school packages, a relatively high degree of dispersion, indicating that the credibility of the data is relatively low. Only from one time server to obtain school-time information, can not correct the communication process caused by the time deviation, while with many time server communication school, you can use the filter algorithm to find a relatively reliable time source, and then use its time to come to school.

Ports for TIME synchronization protocols

UDP 123, TCP 123