Can bind be configured to not drop RR's from the cache when the upstream DNS server is unresponsive
barmar at alum.mit.edu
Sun Mar 27 01:55:14 UTC 2016
In article <mailman.481.1459014144.73610.bind-users at lists.isc.org>,
Ron <ron.arts at gmail.com> wrote:
> On Sat, Mar 26, 2016 at 3:13 AM, Barry Margolin <barmar at alum.mit.edu> wrote:
> > In article <mailman.464.1458924548.73610.bind-users at lists.isc.org>,
> > John Wobus <jw354 at cornell.edu> wrote:
> >> On Mar 18, 2016, at 6:28 AM, Barry Margolin <barmar at alum.mit.edu> wrote:
> >> > In article <mailman.384.1458255932.73610.bind-users at lists.isc.org>,
> >> > Mark Andrews <marka at isc.org> wrote:
> >> >
> >> >> How do you actually expect this to ever work in real life?
> >> >
> >> > I'm pretty sure Google DNS does this. Other resolver operators often get
> >> > complaints about "Why can't I look up <whatever> through your DNS
> >> > servers when I can do it through Google DNS?"
> >> Iâd guessed Google just re-queries before it needs to, which has benefits
> >> but
> >> requires a more complex âclean out very-seldom-used recordsâ strategy.
> >> Iâd imagine they'd use a somewhat-random amount of time to pre-query
> >> as one of their measures against cache poisoning.
> > When I was at Akamai we called this "prefresh".
> > But it doesn't help much if the auth server doesn't respond, the record
> > will still expire.
> >> In any case, I cringe at the thought of overriding TTLs. Theyâre there
> >> for a reason. In some instances, overriding could âhelpâ, but in others,
> >> it
> >> would be really, really bad.
> > The main purpose of TTLs is to ensure that when the record is changed,
> > the new value replaces the obsolete value within the specified window.
> > But if the server isn't responding, clients aren't going to get the new
> > value anyway. Which is more useful for end users, returning the old
> > record past its TTL, or reporting an error saying that the name doesn't
> > exist?
> I think this touches on the heart of the matter.
> We have implemented an ansible-driven emergency plan, where we put
> entries in /etc/hosts files whenever a situation like this happens.
> Not an ideal solution.
And only useful for names you know ahead of time that you're going to
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