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

Danny Mayer mayer at ntp.isc.org
Wed Jun 13 00:43:16 UTC 2007

Jason Rabel wrote:
> I don't think it should re-resolve before every poll/query, but I think it
> would be good if NTP did use and respect DNS refresh/expire info (Actually
> the OS's DNS system would handle it, NTP would just make use of querying the
> DNS instead of fixing the IP after the initial startup).
> If NTP updated IPs according to the DNS info then it would open a whole new
> realm of enhancements, especially for the NTP Pool project.
> First, stale server entries could automatically be removed instead of
> retrying until the end of time (or NTP restarted). A big plus if you ever
> needed to change the IP(s) of some NTP servers but didn't have the ability
> to notify all the users to restart their clients. For the NTP Pool project
> it would allow people to use dynamic DNS services for their NTP servers, and
> also allow the pool to more efficiently load balance contributors. Yes you
> wouldn't exactly have the ultra long-term stability if you end up changing
> all your servers out every few days, but for pool users I think it is still
> acceptable. Also if for some reason for pool users you are unable to contact
> a server or it is way out of whack the 'refresh' with new servers would fix
> that.
> Jason  


This has gotten pretty high on my list of enhancements now that I have
other issues out of the way and some of the other enhancements are
almost ready. However, the work involved is going to be a big effort and
will require patience from everyone, especially me. I did lay out my
methodology somewhere, in hackers I think, and I will post them in the
twiki when I get a moment. Also note that it's going to take quite a
long time before the enhancement propogates to most NTP installations
and this will still leave the issue of the SNTP clients ignoring the
etiquette of usage of NTP servers, not to mention hardware containing
NTP implementations of various lineage.

We should also make sure that our SNTP client follows the same rules.


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