What is Network Time Protocol (NTP)?

Network Time Protocol (NTP) services play a critical role in ensuring the accuracy and synchronisation of time across devices, networks and countries. NTP is the most common protocol used to synchronise the clocks of computers and other network devices to a time source such as an atomic clock.

How does NTP work?

NTP uses a stratum model with the hierarchy based on how close a time server is to the reference clock. The highest level of the hierarchy uses a primary reference time source such as an atomic clock. These sources are highly accurate and provide the most reliable time information. 

What are the benefits of using NTP?

NTP has the advantage of being free, easy to set up and available over the public Internet. It is easy to take time from NTP servers with approximately 3,000 publicly available NTP servers on the Internet today. 

You can find a good overview of what to consider when selecting and connecting to NTP servers in this NTP best practice guide. Netnod provides a free NTP service available to anyone. 

What issues does NTP have?

NTP services typically use connections meant for other data traffic. As these connections are not optimised for highly accurate time, there can be latency and asymmetry issues.

NTP is an old protocol dating back to 1985. It has a number of security issues which make it vulnerable to attacks such as: packet manipulation, replay attack, amplification attack and spoofing. These security issues have been addressed by the recent Network Time Security standard. Netnod’s NTP service was one of the first in the world to offer software and hardware implementations of NTS. 


Networks requiring the highest level of accuracy usually choose a commercial time-as-a-service solution. For networks in Sweden and Denmark, Netnod’s time services can deliver ultra-precise time with an SLA that guarantees accuracy and reliability. The most accurate, secure and reliable time services use Precision Time Protocol (PTP). With time traceable to UTC at the level of nanoseconds (billionths of a second), PTP is far more accurate than NTP especially when delivered over a dedicated fibre. PTP avoids the security, stability and logistical problems of GNSS services and the unpredictable latency and asymmetry issues of NTP.

You can read more about Netnod’s PTP service here.