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

Wolfgang S. Rupprecht wolfgang.rupprecht+gnus200706 at gmail.com
Wed Jun 13 01:22:54 UTC 2007


jason at extremeoverclocking.com (Jason Rabel) writes:
> 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).

DNS refresh and expire are two SOA entities that are meant to be
looked at by the secondaries of a domain.  The refresh is almost
immaterial nowadays since the primary is normally set up to poke all
the secondaries every time the primary starts up or whenever a zone's
serial number changes.  Effectively the refresh is a second or two.
The expire is an option that shouldn't ever matter short of a nuclear
exchange.  It is how long the secondaries are allowed to be
secondaries after the primary is reduced to slag.  It isn't meant as
an end-user TTL, just how long the secondaries can advertise an IP
after the primary goes away.

Now I do think it would be nice for ntp to re-resolve DNS entries at
least once a day.  IP's and CNAMES do change.  In the case of a CNAME
changing NTP won't necessarily even see the ntp daemon at a certain IP
address become unreachable.  It simply won't be the daemon that client
should be talking to any more.  (Eg. dropping out of the ntp pool
shouldn't force one to stop serving all one's other clients also.)

-wolfgang
-- 
Wolfgang S. Rupprecht                http://www.wsrcc.com/wolfgang/
IPv6 on Fedora 7 http://www.wsrcc.com/wolfgang/fedora/ipv6-tunnel.html




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