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

Advanced NTP Topics
This section includes advanced NTP topics and is ideal for experienced users. The
following sections are covered in this section:
• “Stratum Levels and Time Server Hierarchy” (page 58)
• “Configuring NTP using the Configuration File” (page 60)
• “Starting and Stopping xntpd” (page 68)
• “Using ntpq to Query Systems Running xntpd” (page 68)
• “Troubleshooting NTP” (page 70)
Stratum Levels and Time Server Hierarchy
An NTP synchronization subnet is a network of time-keeping systems, called time
servers. These time servers are a subset of the systems on a network or an internetwork.
Each time server synchronizes its time with the the Universal Coordinated Time (UTC),
and measures the time difference between its local system clock and the neighboring
system clocks. These servers are automatically assigned stratum values, which indicate
how close the time server is to the time source.
Stratum-1 Time Servers
Time servers are organized into levels, or strata. Stratum-1 servers are directly connected
to an external time source. The stratum-1 server relies on the external source of time
to provide the correct time, and synchronizes its system clock to that external time
source. The external time source can be a device such as a radio receiver. Figure 4-2
shows the relationship between the GPS receiver time source and the stratum-1 server
associated with it.
Figure 4-2 Stratum-1 Time Servers
58 Configuring NTP