- Having an accurate notion of time has long been a desirable feature
for computers and operating systems. As more computers are networked, it's
important that network applications, be they client/server or peer-to-peer,
have a similar notion of time. This is especially important
for the following reasons:
-
security: It is essential that computers connected to the Internet
maintain accurate time, so that evidence can be gathered in the event of
a break-in to a system. Courts require accurate timestamps on computer
logs so that they may be admissable as evidence.
-
auditing and accounting: It important to know who changed what file at
what time; who was logged in at what time, etc.
-
authentication: Encryption and authentication protocols (such as Kerberos)
require accurate time on both the server and clients.
-
file services: Whether you're using Unix NFS, Novell Netware, or Windows
NT filesharing, it is vitally important that clients and server agree on
the time of day, so that files can be properly synchronized.
The Network Time Protocol (NTP) provides an elegant solution to many of these issues.
NTP is a hierarchical protocol in which nodes attached to highly accurate
time sources such as radio clocks, atomic clocks, and GPSs (Global Positioning
Systems), called in NTP parlance stratum ones, share time among
themselves and provide time to other NTP servers over the network. NTP
servers that get time from one or more stratum one servers are called
stratum
two servers. NTP hosts that get time from stratum twos are called
stratum
threes, and so on. The goal is that organizational entities get time
from several stratum one sources, departmental sources from server
stratum twos, and so on. The higher numbered stratum servers then
distribute time to local workstations.
The goal of the protocol is to provide accuracies up to the order of
a millisecond. The protocol takes into account delays such as network latencies
and computational delays.
In order to provide highly accurate network time to campus hosts,
Communication and Network Services (CNS) operates a Spectracom WWVB Radio
Clock and a Trimble Navigation GPS Clock, enabling us to provide
stratum one support via the Network
Time Protocol (NTP). In addition, CNS operates stratum two servers for PCs, Macintoshes, and personal workstations that are calibrated with our stratum one
servers, and additionally take advantage of the CSG/Surveyor Project's highly accurate GPS clock located on campus.
To synchronize your own computer or server using the Network Time Protocol,
you can use one of the following utilities:
-
Windows 95/NT: About
Time, TimeSync, and Dimension
4 use subsets of the Network Time Protocol to synchronize the PC clock, and will work with the campus servers.
-
Windows 2000: Simple Network Time Protocol is built-in.
-
Macintosh: MacOS 8.5 and higher have NTP built into the Date and Time Control
Panel. Earlier versions can use an application called NetChronometer
.
-
Novell Netware: A freeware rdate program is available, as well as the commercial
Cadence software. Netware 5 supports an NTP server, but there are
some gotchas.
-
Unix: A Unix NTP server package, called xntp,
is freely available. It is already bundled with Solaris, Ultrix,
Digital UNIX, HP-UX, and FreeBSD, and can be compiled on most other variants.
Please note that some of these software packages are fairly complicated
and that CNS cannot provide installation support.
The campus hosts providing NTP services are as follows:
Stratum-1: ntp1-1.berkeley.edu
Stratum-1: ntp1-2.berkeley.edu
Stratum-2: ntp2-1.berkeley.edu
Stratum-2: ntp2-2.berkeley.edu
NOTE: users of Macintoshes and Windows 95/NT should NOT configure
their machines to use ntp1-1.berkeley.edu, as the clients for these operating
systems do not poll the network often enough to accurately measure the network
propagation delay. You will achieve much better accuracy by using
a local server.
NOTE: Due to increasing commodity ISP costs, the UC Berkeley NTP servers are open ONLY to UCB clients, and those of CalREN2 and Internet2. All others are subject to being ignored!
We ask that network or system administrators interested in using ntp1-1.berkeley.edu
as a time server select two or three servers to use it, and then use those
servers to distribute time to their other machines. Please send mail to
ntp@ntp1.berkeley.edu,
telling us what servers are going to be talking to
ntp1-1.berkeley.edu
before configuring your server to use this machine.
For more information about NTP, see the RFC
(Request for Comments) 1305 or the NTP
Home Page. |
