[ntp:questions] Bad NTP servers jeopardizing the pool.ntp.org initiative

Danny Mayer mayer at ntp.isc.org
Tue Mar 27 04:24:28 UTC 2007

Richard B. gilbert wrote:
> Hal Murray wrote:
>>> You don't want to re-resolve anything unless you use up all the
>>> addresses you've already retrieved. We don't do this today and I intend
>>> to fix.
>> I smell a bottomless pit, but it might be appropriate to
>> check the DNS info occasionally.  NTP servers are often
>> up for a long time - long enough that the systems they are
>> using might get renumbered and such.
> It has been a few years since I last operated a DNS server but ISTR that 
> DNS records have a Time To Live (TTL) associated with them and systems 
> don't get "renumbered" often!  At least systems with static addresses 
> don't get renumbered often.  If a server is using broadband cable or 
> ADSL, it may not have a static IP address but, once again, its address 
> is not likely to change while it's up and running.

Correct. However the pool operates differently and you will most likely
 get different addresses each time.

> If there is a problem reaching a server, one might try re-resolving its 
> address but that is by no means the first thing I'd try.

It's not worth while on a normal address at least not usually. What is
worth while is that there may be more than one address for each name so
you really should be trying all of them.


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