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IP-Based Dissemination of Time

Section Q.42

Time Synchronization of Computers using the "Network Time Protocol" (NTP)

For the time synchronization of computers via the Internet, PTB offers several time servers. To disseminate the time information, these servers use the Network Time Protocol" (NTP) which was developed for the synchronization of computers in local networks and on the internet. The protocol is based on the IP protocol used on the internet and it is available for all relevant operating systems.

To be able to use time servers of PTB for synchronizing a computer, you will need a program which supports this protocol. Such programs are available for the operating systems Windows, UNIX, macOS and etc. You can find a list of suitable programs at "Time Synchronization Software" . After installing such a program, you will have to add the address of the NTP servers to be used for synchronization. To use PTB's time servers for synchronization, one or several of the following addresses must be entered:


The time server ptbtime4.ptb.de has been set up at a separate location to improve the reliability of time dissemination.

Authenticated Time Synchronization (subject to fees)

There might be necessity of protected transmission of time information for commercial purposes. PTB runs a service for authenticated time synchronization which meets this demand. For the time distribution it uses the Opens external link in new windowNetwork Time Protocol (NTP) securing it by means of symmetric cryptographic keys.
Companies interested in authenticated time synchronization can apply for the necessary keys. For detailed information see our leaflet Initiates file downloadAllgemeine Bedingungen zur Teilnahme an der "Authentifizierten Zeitsynchronisation" (available in German, only).
This service is subject to fees. Cryptographic keys will be issued for one year. Find more details at Opens internal link in current windowhttps://www.ptb.de/cms/ptb/fachabteilungen/abtz/z14/information-on-ptb-fees.html

This service will be shut down at the end of 2025. New keys will be available until the end of 2024. Authenticated time information can still be obtained via NTS service.

Please contact ntpadmin@ptb.de for further questions.

Network Time Security (NTS)

The method called “Network Time Security“ (NTS) which has been standardized in RFC 8915 (Opens external link in new windowhttps://www.rfc-editor.org/info/rfc8915) by IETF enhances the „Network Time Protocol“ (NTP) with a TLS based and automatic key exchange. This enables client and server to exchange time information in cryptographically secured terms. The calling device establishes a connection similar to a secured one between a browser and a web server and retrieves the necessary kryptographic key meterial before time synchronization starts.

Additionally to NTP the public NTP servers of PTB offer NTS. Prospective users are free to use the service without charge and registering. Starting in 2026 NTS service will replace "Authenticated Time Synchronization".

Please contact Opens local program for sending emailntp-admin(at)ptb.de for further questions.

Please note the following aspects:


Within the limits of the data processing center of PTB in Braunschweig, we do our best to make one of these three time servers accessible at any time. However, we cannot guarantee permanent and disturbance free operation without interruption.


PTB cannot be held liable for damage caused to the users due to failure of PTB`s time service, due to defective transmission by PTB's time servers or due to deviations caused by delays on the internet.

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