[ntp:questions] ntpdate.c unsafe buffer write

Martin Burnicki martin.burnicki at meinberg.de
Tue Feb 12 08:56:47 UTC 2008


David L. Mills wrote:
> The ntpd time constant is purposely set somewhat large at 2000 s, which
> results in a risetime of about 3000 s. This is a compromise for stable
> acquisition for herky-jerky Internet paths and speed of convergence for
> LANs. For typical Internet paths the Allan intercept is about 2000 s.
> For fast LANs with nanosecond clock resolution, the Allan intercept can
> be as low as 250s, which is what the kernel PPS loop is designed for.

Wouldn't it make sense to adjust the time constant depending on the time
after startup, and/or the quality of the responses from the upstream

I.e. the time constant could be smaller after startup to get a fast initial
correction, and then increase depending on the requirements.

The packet delay and jitter should also give a good indication whether an
upstream server is on the local LAN, or on the internet. So the settings
used to make ntpd work well for the worst cases could be used if those
cases apply, but the limitations could be reduced in non-worst cases.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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