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NTP stands for Network Time Protocol. It has the very important job of synchronising clocks over a network.

Time is one of those things that can easily be overlooked. In a network though, have inconsistent time, even just by a few minutes, can cause problems.

Every device on a network will have an internal clock. It's important to keep accurate clocks, otherwise, you may run into issues with correlating logs, SSL certificates, software and the list goes on.

This is where NTP comes in. All of the network devices will sync their clocks to an NTP server which will have the accurate time.

NTP uses a hierarchy system. At the very top, we have the big boys, the MacDaddies. These are highly accurate timekeeping devices such as atomic clocks, GPS or radio clocks. They are known as reference clocks.

NTP uses stratum values to identify the accuracy of a clock.
Stratum levels are between 015, with 0 being the most accurate and 15 being the least. Anything above 15 means the accuracy of the clock is not trustworthy.

Stratum 0 clocks do not connect over a network.
They are directly connected to time servers. They then sync their time and date to the reference clock. These are known as Primary time servers.

The way the NTP stratum model works is by adding a 1 to stratum value at each layer. So, these primary time servers have a stratum 1 value. As we go further down the stratum hierarchy, the stratum value increases as the reference clock is further and further away meaning the time is less accurate.

NTP uses UDP port number 123. So that’s nice and easy to remember.

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