HP-UX Internet Services Administrator's Guide (May 2010)

not vary a lot as more packets are exchanged. Less than 1 millisecond is an excellent
dispersion value for a trip of 15,000 kilometers. The time server in Australia is working
out better than expected at this distance, but it is still noticeably poorer than the other
choices that are in North America.
The time server at Columbia is better than the time server in Australia, due to the closer
distance, but still noticeably worse than all of the other time sources.
You must choose a minimum of one time server, and it is a good idea to choose three
or more for redundancy. Then put lines like this at the end of your /etc/ntp.conf
file:
server ntp-cup.external.hp.com
server bigben.cac.washington.edu
server sirius.ctr.columbia.edu
Backup Time Servers
After selecting the primary time server, you must select two additional time servers
that serve as backup time servers. The closest and fastest time server must be the
primary time server. Backup time servers act as stand-by servers when the primary
time server is not available. The process of establishing backup servers is known as
employing redundancy. Backup time servers ensure that time sensitive applications
have an alternative reliable source for time synchronization.
NOTE: You should select at least three backup servers for redundancy.
The NTP Daemon
The daemon, xntpd, is the network time protocol daemon. It is an operating system
daemon that sets and maintains the system time in synchronization with the Internet
standard time servers. xntpd is an implementation of NTP Version 3, as defined in
RFC 1305 (Network Time Protocol Version 3 – Specification and Implementation). It
is also compatible with the NTP servers Version 1 and 2 as defined in RFC 1059
(Network Time Protocol Version 1 – Specification and Implementation) and RFC 1119
(Network Time Protocol Version 2 – Specification and Implementation), respectively.
xntpd operates in the following modes: symmetric active, symmetric passive,
client/server, broadcast, and multicast mode, as specified in RFC 1305. Abroadcast or
multicast client can deploy a group of workstations without specifying configuration
details specific to the local environment A broadcast or multicast client can perform
the following functions:
• Discover remote server.
• Compute client/server propagation delay correction factors.
• Configure itself automatically.
xntpd reads the NTP configuration file, /etc/ntp.conf, during startup to determine
the synchronization sources and operating modes. You can also specify the configuration
Getting Started with NTP 55