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Network Time Protocol

Here is a basic description for NTP.

For all about NTP, check out this F.A.Q. (Frequently Asked Questions)

Having all devices on the network consistently on the 'real' time will help prevent/limit finger pointing, gives you precise references for troubleshooting, is an industry best practice from several angles, is so easily done (been so for decades) that there is no real excuse to avoid it. Many security systems (especially in the cloud) are now getting so picky that they fail if time drifts too far.

Note that almost all devices with an internal clock are no more accurate than a 5 dollar watch, and their time will drift depending on temperature. At the molecular and atomic level, temperature and vibration are essentially synonymous, and all digital time keepers simply count the vibrations of a crystal or atom, so if the temperate varies, then so will the time. For more info on this or other time topics, just ask Andy, whose roots on the topic go back to the early 1970s when his dad designed and built a couple of atomic timekeepers that look like clocks to most people.

Generally, individual computer users don't need to worry about time, as all the main stream operating systems since the beginning of the 21st Century have had some sort of time updating system in place. This is aimed for people managing a larger group of systems on a network with one or more server type systems.

Pick one to three always on systems to be your NTP servers that get their time from Secondary servers on the internet, preferably from your ISP or at least fairly local to your location. And then have everything point to those internal NTP servers whether they are Windows or Linux servers or your advanced router.

For virtualized systems, make really sure that the base hosts, such as ESX boxes for VMware, have the correct time settings or else you will have all kinds of odd time challenges on their guests.


Many of the time sources will stop serving you if you query them too often, so make sure you set your NTP tool to only check the time once or twice a day. (One day is 86400 seconds). The tactic of checking very frequently is very rude and as such most NTP clients no longer allow the user to mess with that timing setting.

Many organizations already have an internal reference that should be used instead of getting bothering the public time servers again. If they don't already have one, help them arrange this.

I have been using an pair of NTP testing tools from a maker of Time Servers, Galleon. For the easy to read quick checks of different servers, NTP Check, and to log a series of check, NPT Server Tool, that are useful for checking that a server is alive, what level it is, and other useful info.


External references Andy has used:

You have to make sure TCP port 123 is open to the Internet for these to work.

A nice alternative to the static NTP addresses in the table below, are the NTP Pools.
While it is tempting to use just one pointer to one pool, you still want multiple NTP pointers, even if the same pool, just to make sure you get good time in case the one server you get out of the pool has a problem (been there, done that).

List of a few known public NTP servers with IP addresses as of 2015-09-23 Secondary (stratum 2) Secondary (stratum 2) Secondary (stratum 2) Secondary (stratum 2)

Most national governments have their own official time-servers for their citizens that are worth checking out. USA does so via their National Institute of Standards and Technology.

For other time sources, see David Mill's great list at University of Delaware, where you will likely find more about NTP than you will ever want (I'm still working through it).

Please use the secondary time sources as much as possible, only use the primary's if you have the justification and know what you are doing, in which case you probably don't need this page.
For more sources, do search with a tool like for the following keywords "ntp stratum public servers" is another resource of NTP info

For other Time related information, see the NRC's WebClock Canada and USNO's Master Clock Time.

For the only real Date and Time display standard, read up on the ISO8601 standard. For a drier reading, there is's write-up. Or for easier reading, Markus Kuhn has a nice recommended write-ups. And then there is the XKCD style

Older platforms may not have a built-in NTP client. In those days when I first wrote this page it was to collect some useful pointers that may or may not still be of use, but are certainly of some historic value and are retained for that purpose. Also, I have found enough old systems hiding in the most interesting places, so one never knows what will be tripped over and need resources for. I likely have these still in my stash of older files, so if you can't find else where, do send me a message via the address on the bottom right.

Win2K/NT4/Win9x and such can sync using third party tools such as:

NetWare 5 and higher has support for this built for this within the TimeSync function built in to the core operating system.
Make sure the server polling external NTP sources has its TimeSync parameter "Polling Interval =" set to 60000 or higher instead of the default 600. I would not go any higher than 600000 (almost a week) otherwise you will start getting large enough corrections at those times that it would be noticeable if your system's clock is drifting quickly.
NetWare 5.1SP5 and higher are also trivial NTP servers that can be pointed to as an internal time source. Up to at least NetWare 6, some UNIX/Linux boxes are looking for more NTP data than NetWare provides so in those cases you may need to make those UNIX type systems the primary time-servers on your network with NetWare pulling UNIX.

NW 3 & 4 can sync using a third party tools such as RDATE from;

Last updated 2021-08-24 Copyright © 1996-2022 Andy Konecny andyweb @