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 well-known, highly accurate servers or

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

 

time-keeping is an essential part of the operation of the Webcache.

 

 

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.