Installing and Administering Internet Services

Chapter 7 301
Configuring the Network Time Protocol (NTP)
Advanced NTP Topics
administrative domains, and should be accessed from different
gateways and access paths. Avoid loops and common points of failure.
Do not synchronize multiple time servers in an administrative
domain to the same outside source, if possible.
• For enterprise networks that contain hundreds or thousands of file
servers and workstations, the local time servers should obtain service
from stratum-1 servers.
• When defining a relationship between a server of a higher-numbered
stratum and a server of a lower-numbered stratum, configure the
relationship in the server of the higher-numbered stratum. 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, since there is likely to be more
configuration change in systems of higher-numbered stratums, such
as workstations.
Configuring NTP using the Configuration File
This section describes the statements that can be defined in the
/etc/ntp.conf configuration file. Configuration file statements are
described in the following subsections:
• “Configuring Relationships with Other Time Servers” on page 301
• “Configuring External Clocks” on page 303
• “Configuring a Driftfile” on page 305
• “Configuring Authentication” on page 305
• “Restricting Incoming NTP Packets” on page 307
Configuring Relationships with Other Time Servers
The roles of a time server are its relationships to other servers in the
synchronization subnet. In the configuration file, a role is defined with
one of four statements (peer, server, broadcast, and
broadcastclient):
peer host | IP_address specifies that the named host is to provide time
that the local host may synchronize to, and the local host is willing to
provide time to which the named host may be synchronized.
server host | IP_address specifies that the named host is to provide
time that the local host might synchronize to, but the local host does not