HP-UX Internet Services Administrator's Guide (February 2007)

Table 4-5 Output from ntpq for Configuring Silicon Valley Time Server
remote refid st t when poll reach delay offset disp
=========================================================================
*REFCLK(29,1) .GPS. 0 l 25 32 377 0.00 0.413 0.03
+bigben.cac.wash .USNO. 1 u 56 64 377 39.54 -0.466 1.68
clepsydra.dec.c usno.pa-x. 2 u 122 512 377 6.32 -0.250 0.92
-clock.isc.org .GOES. 1 u 149 512 357 5.98 -3.045 0.46
hpsdlo.sdd.hp.c wwvb.col.h 2 u 25 32 126 56.29 -8.078 8.50
+tick.ucla.edu .USNO. 1 u 13 64 177 19.29 -0.265 0.26
+usno.pa-x.dec.c .USNO. 1 u 56 64 277 6.82 0.034 0.20
gpo.adelaide.ed tictoc.tip 2 u 15 16 377 470.52 54.789 0.90
sirius.ctr.colu NAVOBS1.MI 2 u 3 16 377 83.37 -8.372 1.24
The time server in Australia has a delay of 470 milliseconds, which is very similar to
the ping round-trip times seen earlier. This leads to an offset value of 54 milliseconds,
which is significantly worse than any of the other time sources. It is interesting to note
that the offest is much less than the delay, which means that the round-trip is almost
symmetric. NTP must assume the outbound and inbound travel times are equal, and
the offset value gives an idea how unequal they might be. This is considerably better
than 470/2 which would be the offset if NTP did not make this assumption. Also
interesting is the very low dispersion value, which means that the round-trip time does
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
56 Configuring NTP