68CHAPTER 5: SYSTEM TIME
What is the | The Network Time Protocol (NTP) is used to synchronize the time of client |
| Network Time | machines and servers with other |
| Protocol? | reference time sources. It maintains a consistent Coordinated Universal |
| Time (UTC) within your network which is far more accurate than the |
| internal system clocks of client machines and prevents time drift from |
| occurring on the Webcache. |
| NTP provides client machine and server time accuracies typically within a |
| millisecond on LANs, relative to a primary NTP server synchronized to UTC |
| via a Global Positioning Service (GPS) receiver. Such accurate |
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| Choosing a | You can choose to use one of the many public NTP servers that are |
Network Time | available on the Internet or set up your own NTP server. When you have |
| Protocol Server | access to an NTP server, you can configure the Webcache to determine |
| the current time using NTP; see “Configuring the System Time Using the |
| Network Time Protocol” on page 69 for more information. |
| Public NTP servers are grouped into stratums. The NTP primary (stratum 1) |
| servers are connected to a reference clock, which is typically an expensive |
| cesium clock or cheaper GPS receiver. Servers operating at stratum 1 are |
| the most accurate available, but also the fewest in number because of |
| the prohibitive cost of reference clocks. |
| The NTP secondary (stratum 2) servers are in turn connected to a stratum |
| 1 server and are therefore less accurate but greater in number. Stratum 3 |
| servers are connected to stratum 2 servers, and so on, up to an imposed |
| limit of 15 strata. You should not use a high level public stratum server |
| because of their limited number and because the load placed on them is |
| increasingly heavy. |
3Com recommends that if your network has an internal NTP server, you should use this rather than a public stratum server. If not, you should use the lowest stratum public NTP server available to you.