Configuring The System Clock; Synchronization - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - SYSTEM BASICS CONFIGURATION GUIDE 2010-10-04 Configuration Manual

Copyright © 2010, Juniper Networks, Inc.
NOTE: When the system is not configured as either an NTP client or an NTP
server, it responds to NTP requests with an invalid stratum number.

Synchronization

There are three stages to synchronization:
Preliminary synchronization
Frequency calibration
Progressive synchronization
Preliminary Synchronization
Preliminary synchronization is a stage during which the system evaluates the initial time
situation and decides how to proceed with longer-term synchronization. This stage
involves the following steps:
The system obtains several readings of time data from NTP servers.
1.
The system analyzes time data in the messages and compares the readings from
2.
different servers. Using this information, the system identifies the initial best time
source (the best server).
The system calculates the difference between its own clock and the best server's
3.
clock (the offset) and proceeds as follows:
If the offset is greater than 15 minutes, the system disables NTP and displays a
message advising you to check the time zone and clock settings.
If the offset is less than 15 minutes, the system sets its clock to that of the best
server.
Provided the system has not disabled NTP, it proceeds to the next stage:
4.
If a frequency calibration is available, the system starts progressive synchronization.
If the system has never performed a frequency calibration or the calibration has
been deleted, the system starts a frequency calibration.
Frequency Calibration
Frequency calibration takes place the first time you use NTP or when you reboot the
system. During this stage, the system evaluates the frequency error of its clock by
measuring change in the offset error. A frequency calibration takes 15 minutes.
Progressive Synchronization
After the system has established initial NTP parameters, it continues to synchronize to
a server as follows:
The system acquires time information from servers periodically.
1.
The system evaluates which server is currently the best time source (the master) by
2.
analyzing time data in the messages and comparing the data from different servers.
Chapter 10: Configuring the System Clock
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