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

David Woolley david at ex.djwhome.demon.co.uk.invalid
Wed Jun 20 21:24:09 UTC 2007


In article <46790346$0$13852$ba620e4c at news.skynet.be>,
Jan Ceuleers <janspam.ceuleers at skynet.be> wrote:

> - the ntpd development team don't think it is a good idea to re-resolve 
> before _every_ poll/query, but do think it is a good idea to do this 

What may not have been clearly pointed out is that re-resolving is a
very expensive operation for ntpd, as the standard resolver libraries
are blocking, so, to avoid blocking ntpd itself, it has to spawn a
separate process to do the resolution.  (This actually generates a
relatively frequently asked question because people see two processes
when it is starting and thing something has gone wrong.)

> 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.




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