goofyzig,
This issue is widely misunderstood; yours is the second such message to
me today. So, please spread the word.
When a server loses all sources it does not necessarily become
unsuitable for downstream clients. Ordinarily, it inherits error
statistics from upstream servers and provides them to downstream
clients. Servers and clients use these statistics to calculate the
maximum error statistic which represents the maximum clock error
relative to the primary reference clock. See the error budget called out
in the specification. Once determined, the maximum error increases at a
rate (15 PPM) determined as the maximum disciplined clock frequency
error of the server clock. This increase continues indefinitely or until
the sources are again found.
Downstream clients monitor the maximum error against the selection
threshold, by default 1.5 s. Once exceeding the threshold, the server is
never selected for synchronization. Note that, even at this level the
server may still be a credible choice, as the expected clock frequency
error of a disciplined oscillator is usually within 1-2 PPM. Meanwhile,
if there are other sources for the downstream clients, these sources
quickly capture the selection process and the server without sources
becomes irrelevant.
Dave
goofyzig wrote:
Hi there. A quick question about what to expect when it comes to NTP
failures. I configured a Meinberg NTP server (software-based server),
had it working, serving time to the back-end hosts, Reachability at
377 for its two NTP upstream time sources (internet NTP servers).
Once configured, I wanted to see how the server failed.
My expectation was that once Reachability went to zero, the server
would stop serving time since it no longer has a source itself. So I
blocked port 123 UDP/TCP at the firewall, and sure enough,
Reachability for the two upstream sources slowly wound down from 377
to zero. However, once Reachability got to zero, the Meinberg NTP
server CONTINUED to serve time, and CONTINUED to say that each of the
two upstream servers were believable, as if it was still getting time
from them (but it was not). I confirmed the drops at the firewall.
The Reachability was at zero, so I know the Meinberg software was not
getting NTP time from anywhere. Yet, it kept serving NTP time to its
back-end hosts, and kept saying that ach of the two upstream servers
were good (one colored green, the other yellow, with the * and the +
signs next to them). After 5 hours of zero Reachability, nothing
changed.
So my question is: how long does it take before the Meinberg server
declares itself in a "failed" state and stop serving NTP? Is that how
it's supposed to work? I looked all over the Meinberg site and could
not find any forum or literature regarding how the NTP server is
expected to fail. Maybe Im missing a setting? Thanks for any
help!!! :)
Goofyzig
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