've included here, but hopefully this chapter will help to dispel some of the trepidation many people have about what's coming in the future. IPv6 is not that difficult, really. Sure, the addresses are huge, but once you spend some time with it, you'll learn how to see the addresses as network and host addresses. Chapter 37: IPv6 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. aj-1uj-1 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 Hz). 1080p high-definition televisions update their screens at 60 (or 120, 240, or even 480) frames per second. Modems, Tls, DS3s, and all other data services send information at a set number of bits per second. When two pieces of equipment communicate, they must agree on the length of a second. For a long time, a second was defined as 1/86,400 of a sidereal day (24 hours * 60 minutes 60 seconds = 86,400 seconds