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Network Warrior, 2nd Edition by Gary A. Donahue

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Chapter 38. Network Time Protocol

The Network Time Protocol (NTP) is an Internet protocol used for synchronizing a device’s clock with a reference source across a network. When accurate time is required on your networking equipment or computers, you should use NTP—in other words, you should always use it.

NTP was originally defined in RFC 958. The last documented version is version 3, which is defined in RFC 1305. To learn more about NTP, check out its home page: http://www.ntp.org.

The interesting stuff relating to how NTP really works is found in RFC 1129, which is available only in PostScript or PDF format. If you get excited when you see the type of math shown in Figure 38-1, RFC 1129 is for you.

Actual math from RFC 1129

Figure 38-1. Actual math from RFC 1129

If, like most people I know, you can’t be bothered with the math and just want to know what you need to do to make NTP work for you, read on.

What Is Accurate Time?

How do we measure time? How long is a second? Who defined how long a second is, and why does it matter? These are questions most people don’t think about. Most of us take time for granted.

Every electronic device you own, from your personal computer to your television, relies on time being accurate to a certain degree. The power in your home oscillates at 60 cycles per second (60 Hz). 1080p high-definition televisions update their screens at 60 (or 120, 240, or even 480) frames per second. Modems, ...

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