HP-UX Internet Services Administrator's Guide (August 2003)

Configuring NTP
Advanced NTP Topics
Chapter 478
• Every NTP hierarchy must have atleast one stratum-1 server. You
can configure the administrative domain to contain outside sources
of synchronization, which ultimately link to stratum-1 server, or you
can implement your own hierarchy of NTP time servers with one or
more stratum-1 servers.
• Configure atleast three time servers in the administrative domain
because it is important to provide multiple, redundant sources of
time synchronization. NTP is designed to select an optimal source of
synchronization from several sources. Each time server must be a
peer with each of the other time servers.
• For each time server, select one or three outside sources of
synchronization. This assures a relative degree of reliability in
obtaining time, when you select sources that do not share common
paths. The sources must operate at a stratum level that is one less
than the local time servers.
• Each outside source of synchronization must be in different
administrative domains, and you must access the sources from
different gateways and access paths. You must avoid loops and
common points of failure. Do not synchronize multiple time servers
in an administrative domain to the same outside source.
• For enterprise networks that contain many file servers and
workstations, the local time servers must obtain service from
stratum-1 servers.
• While defining a relationship between a higher-numbered stratum
server and lower-numbered stratum server, configure the
relationship in the higher-numbered stratum server. For example, if
a stratum-3 server is a client of a stratum-2 server, configure the
relationship in the stratum-3 server. This simplifies configuration
maintenance, because configuration of the higher-numbered stratum
server changes often.
Configuring NTP using the Configuration File
This section describes the statements that you can define in the
/etc/ntp.conf configuration file. It discusses the following topics:
• “Configuring Relationships with Other Time Servers” on page 79
• “Configuring an External Clock” on page 81
• “Configuring a Driftfile” on page 82