NTP and system Clock

[Sreejith Kaliyam]

Hi

I am setting up a Local NTP server (Local system clock) (I cannot connect to any external time sources). I have a oracle RAC running in my network, which is too much time sensitive and its time should not go backward.

Please find below the scenario and suggest me solution.
Iam using one HP-UX server as my NTP source and other servers and taking time from my local NTP server.If my Local NTP goes down for some time and accidently coming up with a time which is backward than the actual time, do my other servers update their clock backward?.. Or does it lagg their clock for syncing with the NTP source. If my RAC servers are updating to the backward time, my application would crash. Kindly advice me..

Regards

Sreejith K

[Steven E. Protter]

Shalom,

Nothing is going to get updated back in time.

First, you can adjust your system clock during a maintenance window without impacting oracle at all.

When ntp sees a system running fast, it does not turn back the system clock. It runs the system time more slowly than real time so a gradual adjustment occurs until there is sync.

If for example it finds the system time 10 seconds fast, it will run its own clock slightly slower than normal until the system time is in sync with the ntp source.

When a system is running and syncing to ntp and loses synch there is no sudden change. The system runs from then on based on how much time has passed on its system clock.

SEP

[Rita C Workman]

If your master time server goes down and then comes up later the others will do what can be called lagg their clocks back into sync with the master time server.

If, however, there is a significant time difference then they will not get back into sync with the master and time will have to be adjusted manally. There is only so far, time syncing will allow a difference.

Do some research...man xntp, ntpdate, clocks, ntpq

Rgrds,
Rita

[James R. Ferguson]

Hi:

If your firewall prevents outside connection, as least consider allowing port 123 traffic for NTP to be opened for your server.

Otherwise, you have the choices of a radio receiver or, as already stated, synchronization to your own internal server.

Regards!

...JRF...

[A. Clay Stephenson]

There is a fundmental flaw in your design. What happens when your NTP server fails? One of the most basic tenets of NTP is that multiple time servers should be used. Sadly, in your case nothing can be trusted and your time is guaranteed to be wrong all the time and almost certainly will be drifting in one direction so that your systems' times and true time will never converge. If you are not allowed to use external time sources then you should really get a timesource such as a GPS timesource so that you are not exposed to vulnerabilities. I would then designate at least 2 of your servers as NTP servers which sync to this GPS time source AND have a drift file so that when the GPS synchronization fails, the servers have a very good notion of how their system clocks drift with respect to true time and can compensate.

[Sreejith Kaliyam]

Hi

Thanks for the immediate response. I was doubting about this. I can convice my customer now. I am closing this thread.

Regards

Sreejith K

[Sreejith Kaliyam]

Thanks