[ntp:questions] How should an NTP server fail?

goofyzig backup757 at gmail.com
Sat Jun 5 01:01:14 UTC 2010

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

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!!! :)

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