windows time update server

Background

At the end of the last century, the owners of corporate local networks faced the problem of synchronizing time within the network with the reference time. Manufacturers of synchronization and common time systems have proposed to solve this problem a whole class of local area network synchronization devices, called clock servers(or time servers - time server). At that stage in the development of network solutions, there was a need for a local synchronization device that receives accurate time signals from a reference source and synchronizes a single local network. The cost of such devices ranged from 2,000 to 5,000 euros. Designers of functional buildings (air terminals, hotels, banks, ...) included these devices in projects as the only Possible Solution tasks of network time synchronization with reference time.

To date, the cost clock servers like devices has not changed. But on the World Wide Web, such public resources as time servers. Thus, at the time of the implementation of projects that include clock servers As devices, LAN owners are faced with a dilemma: synchronize local network with expensive device or free online resource.

Device or network resource

It's obvious that clock server in the form of a device is needed where there is no access to the Internet. If timing accuracy with a time reference greater than 100 milliseconds is required, use clock server in the form of a device. An example of such a device is DCF-NTP converter offered by Chronotron , designed to synchronize single time systems and computers in local network enterprises.

If there are special requirements for reliability (navigation system, process control, traffic control, ...) it is preferable to use clock server in the form of a device, not forgetting that the device itself can fail.

In all other cases (banks, hotels, business centers, …) time server as a network resource is fully suitable for solving the synchronization problem.

How to sync over the Internet

operating room WINDOWS system XP has a tab in the default date and time settings called "Internet Time" that allows the user to periodically synchronize their PC with an Internet time server. By default, you are offered a choice of, for example, two time servers: time.windows.com or time.nist.gov. But there are many other time servers on the Internet, including domestic ones, and you can easily add them to the existing ones and synchronize using any of them. The standard WINDOWS XP synchronization program does not always work correctly, and the discrepancy between the system time and the standard can reach 2-3 seconds.

For synchronization with an accuracy of up to 100 milliseconds, you should use software products from companies that are professionally involved in unified timing and synchronization systems. One such firm, Symmetricom, which makes a ton of professional synchronization equipment (including clock servers), has developed a free software product called "SymmTime™". This program allows you to synchronize a PC using any time server from the list or several servers at once, as soon as it is available. Synchronization is carried out periodically or once at the start of the program. You can see the status of synchronization and the amount of discrepancy with the standard. The program has an advanced user interface that allows you to configure time zones, the type and number of hours displayed on the program panel. The synchronization accuracy with this program is no worse than hundreds of milliseconds and is almost as good as the synchronization accuracy with the clock server, since the methodological algorithm for synchronizing with remote server and the server located in your local network is the same.

The address of Symmetricom, where you can download the above program: www.symmetricom.com

Some time server addresses
time.symmetricom.com	clock.nc.fukuoka-u.ac.jp
nist1.symmetricom.com	fartein.ifi.uio.no
ntp1.symmetricom.com	ntp1.strath.ac.uk
ntp2.symmetricom.com	swisstime.ethz.ch
ntp3.symmetricom.com	time1.stupi.se
clock.isc.org	timex.cs.columbia.edu

Connection to the NTP server is available to everyone, does not require the installation of additional software and is completely free. Server address to use in settings operating systems or equipment:

website

Synchronization works via UDP port 123. To get the time from the NTP server, check that the firewall does not block this traffic.

When setting up equipment to synchronize time with a free NTP server, the best solution is to use the server name, not its IP address. If the server location changes, sync by name will continue to work without the need to change settings. If the equipment supports the ability to configure synchronization only by IP address, then if the server address changes, it will become impossible to request the exact time from it and you will have to change the settings. You can find out the current IP address of the server using the nslookup command site

Please do not set up time synchronization via Task Scheduler or Cron! This setting results in peak server loads at the beginning of every minute, hour, or day.

Setting up synchronization after a certain time interval (for example, once every 5 minutes) does not make sense, since in such an interval the clock accuracy of even the simplest devices is sufficient to maintain accurate time. Both Windows and Linux have services specifically designed for time synchronization. The built-in algorithms of operating systems independently evaluate the accuracy of the clock and request synchronization only if it is really necessary.

During the entire time of operation of the free Mobatime NTP server, periodically, some clients send an unreasonably large number of requests per second to the server. Currently, several clients are requesting synchronization at up to 500 requests per second each. We are forced to use specially designed software to automatically detect and close access to the time server to such clients.

The same software detects clients that have set up Scheduler or Cron synchronization and puts their IP addresses on the list of unserved clients for several days. If your system has stopped receiving time from the NTP server, then make sure there are no errors in the settings and check the frequency of synchronization requests. You can do this using a sniffer by configuring it to collect traffic between your system and the NTP server via UDP protocol on port 123. If ipfw is used, then the number of requests can be quickly estimated by looking at the output of the ipfw -a list command For a rule that allows traffic to NTP server, the counter should increase slightly.

If you support a large local network, then set up synchronization on any server with the Mobatime NTP server and install your NTP server on it. It will work in the second stratum and provide accurate time to the entire local network. Passing time requests from all clients of a large local network (hundreds of jobs) through NAT to an NTP server is a bad idea. Most likely, after a short time, the server will refuse to serve so many requests from one IP address. If the network is built on software Microsoft uses a domain structure, then in order for all users to receive the exact time, it is enough to set up synchronization with the NTP server only of domain controllers. All clients will receive the exact time from them automatically.

Keep in mind that Kerberos will stop working if the client and server times differ by more than 5 minutes. It is also necessary to remember about the mandatory setting of time synchronization between guest systems and the host or time server when using virtualization.

We have published a short article on how NTP synchronization works, and why when synchronizing time over the Internet, the remoteness of the client from the NTP server does not matter.

If the operation of your system requires the constant availability of the most accurate time and you do not want to depend on the stability of data transmission channels, then our specialists are ready to advise you and help you choose an NTP server for installation in your data center or server room. Our contacts can be found on the website. We carry out the whole range of works in Europe, Russia and India, including installation and subsequent maintenance of time systems, clocks with the symbols of your company installed indoors or outdoors, information boards, and so on. A wide range of products and accumulated experience allow us to build systems for servicing airports, subways, business centers and create clock systems for entire cities. Clocks on the streets of such a city always show the exact synchronized time and work even in the most severe frosts.

Everyone is already used to the NTP time synchronization service - it is enabled by default or easily enabled for most popular operating systems. However, what accuracy is achieved in this case? What are the exact time servers, and with which mere mortals can work? What are the pitfalls, and how to choose the "right" time servers?

Server types

Servers are Stratum 1 and 2, 3 (rarely higher).

Stratum 1- get the exact time directly from the exact time source: atomic clock (eg time-a.nist.gov, accuracy - trillionths of a second) or GPS receiver (ntpx.imvp.ru accuracy - billionths of a second). There are servers that receive the exact time via the CDMA cellular network (millionths of a second). When working with ntpd, you can find out the type of server with the ntpq -np command: "PPS" means GPS, "ACTS" means a direct connection to the atomic clock (there are other valuable statistics - ping, ping jitter (jitter), server rank (1 ,2...)).

"Mere" mortals are strictly prohibited from accessing Stratum-1 servers. the load on them is already very large (and many Stratum-1 servers do not have public access at all). It is believed that you can connect to Stratum-1 servers or request access to them if you keep an NTP server serving at least 100 clients. Full list servers can be seen here: support.ntp.org/bin/view/Servers/StratumOneTimeServers . Naturally, it is desirable to connect to servers in your country.

Stratum 2- get exact time from Stratum-1 servers. With proper configuration and selection of exact time source servers, they have an error of less than 1ms. Usually everyone can connect, but many servers regularly die from load (for example, time.windows.com). www.pool.ntp.org maintains round-robin lists of public Stratum-2 NTP servers. This ensures load balancing, and they are almost always available. You can connect to these servers at 0.ru.pool.ntp.org 1.ru.pool.ntp.org 2.ru.pool.ntp.org and 3.ru.pool.ntp.org (this is for Russia, selected randomly from a list of ~50 servers).

Stratum 3- get time from Stratum-2 servers, etc.

Practical Precision

Stratum-1
This is a graph of the difference between the system time and the time received from Stratum-1 servers (canonical.com - Stratum-2 server, for comparison).
*.nist.gov - located in the USA, because of the "big" ping, terrible "emissions" sometimes happen. Error from Russian Stratum-1 servers is usually within +- 1ms.

Stratum-2
This is the difference with Stratum-2 servers: 4 from the Russian pull, 1 from the European one, default ubuntu time server (europium.canonical.com), and the same *.nist.gov:



Servers that have a constant error of up to 20 ms immediately catch the eye.

Summary

PS. By the way, by default in Ubuntu, time synchronization occurs once at system boot. If the uptime is under half a year, the time can go a lot. Install ntpd - it corrects the time constantly and "smoothly" (without sharp jerks, "smearing" the slowdown / acceleration of time). In Windows, synchronization occurs once a day for a week in one "jump", which can cause difficulties when processing logs if there is a big difference.

Comrades!

You give a large public NTP servers in Russia! Especially Stratum-1 (we generally have a hard time with them, 2-3 pieces for the entire exUSSR). By the way, the exact time can also be taken from Glonass, who will undertake to launch the first Glonass-powered server?

P.P.S. I can’t figure out which blog to transfer to, tell me :-)