Installing and Administering Internet Services

Chapter 7 219
Configuring NTP
Configuration
but if the remote server does not meet the criteria for an authenticated
synchronization source, it will never be used as a time source by the local
host. See “Configuring Authentication” on page 221.
NOTE xntpd is an HP implementation of version 3.2 of a publicly-available
NTP daemon. HP does not guarantee that xntpd is fully compatible with
version 1 or version 2 implementations of the daemon.
Configuring External Clocks
You can configure xntpd to support an external clock. Clocks are
normally configured with server statements in the configuration file.
Clock addresses can be used anywhere else in the configuration file that
a normal IP address is used—for example, in restrict statements.
Clocks are referenced by an address of the format 127.127.t.u, where t
specifies the clock type, and u is a unit number, which is dependent on
the clock type for interpretation (this allows multiple instances of the
same clock type on the same host).
xntpd supports two kinds of clocks:
• Netclock/2 WWVB Synchronized Clock. A system with this type of
clock attached and configured is, by definition, a stratum-1 time
server. The address used to configure the clock is 127.127.4.u,
where u is a value between 1 and 4. You must create a device file
/dev/wwvb%u.
• Local synchronization clock, also known as a “pseudo” clock. A system
with this type of clock configured uses the local system clock as a time
source. The address used to configure this clock is 127.127.1.u,
where u is a value between 0 and 15 and specifies the stratum level at
which the clock runs. The local host, when synchronized to the clock,
operates at one higher stratum level than the clock. This type of clock
can be used in an isolated synchronization subnet where there is no
access to a stratum-1 time server.
See the xntpd man page for more information on configuring external
clocks.
Figure 7-7, shown earlier in this chapter, depicts an example of servers
in a synchronization subnet and their relationships to each other. Figure
7-9 shows the peer, server, and broadcast statements that are configured
for each of the servers. The system that will assume the server role is