RuggedCom RuggedRouter RX1100 - Manual (Page 257)

29. Configuring NTP
Revision 1.14.3 257 RX1000/RX1100™
29.1.1.1. The NTP Sanity Limit
The NTP daemon corrects the system time through two means, "stepping" and "slewing". If the
difference between the local clock and the reference chosen by NTP (the "offset") is more than 128ms
for a period of more than 900 seconds, NTP will "step", or instantaneously correct, the time. If the
time difference is less than 128ms, NTP will "slew" the time by no more than 500 microseconds every
second toward the correct time, in such a way that to an application on the system, the time never
appears to be flowing backwards.
NTP will step the system time when it starts up. This is almost always at boot time. Stepping the time
afterwards can cause protocols (such as OSPF) that rely upon accurate real time to fail. The router
deals with this problem by restarting these protocols if they are running when NTP restarts.
After booting, NTP uses slewing to achieve synchronization by making small and frequent changes
to router hardware clock. If the reference server's clock differs from the local clock by more than 1000
seconds, the NTP daemon decides that a major problem has occured and terminates.
Usually, NTP will succeed in synchronizing the clock at boot time. If it fails to synchronize the clock
(perhaps due to a downed WAN link), the NTP daemon may terminate. The router, however, will note
the termination and will automatically restart the NTP daemon.
29.1.1.2. NTP And The Precision Time Protocol Card
If the router is equipped with a Precision Time Protocol card, NTP will treat the Global Positioning
System signals received from the card (when GPS locks) as a stratum 0 reference clock. The router
will always preferentially use this reference above all others.
29.1.1.3. Included With NTP
Your RuggedRouter software includes the ntpq, ntpdc, ntptrace and ntp-keygen command line utilities.
The ntpq utility program can be used to monitor the NTP daemon operations and determine how well
it is running. The ntpdc utility program is used to query the NTP daemon about its current state and
to request changes in that state. The ntptrace utility is a utility trace a chain of NTP servers back to
the primary source.
The ntp-keygen utility can be used to generate secure public keys for authentication.
29.2. NTP Configuration
29.2.1. NTP Server Main Menu
Figure 29.1. NTP Server