[time-nuts] can of worms: time-of-day in a community radio station

[Steven Sommars]

Each NTP Pool server's real-time status can be seen at
https://www.ntppool.org/scores/*ip_address*
I can't answer questions about the monitor's source code
<https://github.com/ntppool/monitor >

NTP server timestamp errors happen occasionally.  Internet delays and
losses are unpredictable. My paper
<http://leapsecond.com/ntp/NTP_Paper_Sommars_PTTI2017.pdf> discusses such
NTP time transfer issues (thanks Tom).
A diverse set of servers may be desirable:  Using eleven stratum 2 servers
with common stratum 1 sources may not meet your requirements.
If the bad guys can intercept NTP traffic timestamps can be altered, unless
NTP authentication is used.  [This rarely happens.]





On Mon, Nov 4, 2019 at 2:51 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> Since “rogue” servers are rare, bumping up the number of servers fairly
> quickly
> gets you to a very high degree of confidence. Is that 5, 7, 9, or 11? It
> sounds like
> a wonderful topic for somebody’s thesis or dissertation :)  Given that
> this is a free
> resource and that the network usage is negligible even with a dozen
> servers, the only
> real downside is being tagged as a resource hog.
>
> Bob
>
> > On Nov 4, 2019, at 7:05 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> >
> >
> > attila at kinali.ch said:
> >> This is a pretty baseless fear. The servers in the ntp pool are
> constantly
> >> monitored and those that are off by more than 100ms are quickly removed
> >> (within 2-3 hours, IIRC). Of course, if you are already using one of
> those,
> >> then the removal will not help you. But you are most likely using 3-5
> servers
> >> anyways, which means ntp will remove the "rouge" server on its own.
> >
> > It's more complicated than that.
> >
> > It depends on what code you are using and how you configured things.
> >
> > If you are using  ntpd and you said in your ntp.conf
> >  server <pool>
> > Then it grabs one and sticks with it until you restart ntpd.
> >
> > In the old days, it was common to use
> >  server 0.pool
> >  server 1.pool
> >  server 2.pool
> >  server 3.pool
> > That used the pool before the pool code in ntpd was working.  I'm pretty
> sure
> > some distros set things up that way and some systems are probably still
> using
> > an old config file.
> >
> > The pool code is supposed to drop bad servers and get replacements.  I'm
> not
> > sure of the details on what "bad" covers.  It could be not responding at
> all
> > or it could be time not good-enough.  I'll dig into the code if it
> matters.
> >
> >
> > If you aren't running ntpd (classic or ntpsec) then I don't know what
> happens.
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
> >
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