RuggedCom RX1100 NTP Sanity Limit, NTP And The Precision Time Protocol Card, Included With NTP

Chapter 22 – Configuring NTP

The NTP Sanity Limit

NTP changes the system through “stepping” and “drifting”. Stepping is a sudden change of time whereas drifting is a slow gradual time change.

NTP will step the system time when its starts. 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 drifting to achieve synchronization by making small and frequent changes to router hardware clock. If the synchronizing server's clock differs from the hardware clock by more than 1000 seconds, the NTP daemon construes a major problem 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 restart the NTP daemon.

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.

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.

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