[ntp:questions] Best practice: re-resolve server IP addressbefore each poll/query

Danny Mayer mayer at ntp.isc.org
Sat Jun 23 15:14:31 UTC 2007

Jason Rabel wrote:
>>> I was wondering what the impact of such re-resolving behaviour would be 
>>> on the pool. Both cases are relevant, I think: best-practice recommended 
>> It would be a serious problem for clients of the pool as it would cause
>> them to hop servers, thus invalidating the statistics previously 
>> accumulated, every time that TTL ran out.  pool names are expected *not*
>> to resolve to the same machine on each request.
> But if you set a high TTL for the pool DNS (say weekly or even bi-weekly)
> then it would give the benefit of removing stale servers and when ntp
> refreshed it *should* get a working server (since the pool has its own
> health check).
>>From what I hear people say, it seems like NTP is the one having to do all
> the DNS resolution and whatnot locally? Wouldn't (or shouldn't) that be
> handed off to the OS for some other process to do the lookup and manage the
> TTL and cache and all that?

No, the O/S is the one responsible for the lookups. We don't manage this
within NTP it would be a waste of time and effort even with my knowledge
of the internals of DNS. We just use the standard calls and the O/S uses
whatever means necessary to find a resolver and get back a response.


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