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

Planning a Multiple-Server NTP Configuration
You must consider the following guidelines when planning your configuration:
• 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” (page 60)
• “Configuring an External Clock” (page 62)
• “Configuring a Driftfile” (page 63)
• “Configuring Authentication” (page 64)
Configuring Relationships with Other Time Servers
The role of a time server depends on its relationship with other servers in the
synchronization subnet. In the configuration file, you can define a role using one of
the following statements for peer, server, broadcast and broadcastclient:
60 Configuring NTP