[dns-operations] TTL=0

Greg Choules gregchoules at googlemail.com
Fri Jan 18 22:18:40 UTC 2019

Hi Fred.
No, I am not talking about dscacheutil or any particular client software. I
just want to know whether, in the opinion of the world's DNS professionals,
recursive servers should or shouldn't ever send answers from cache with

cheers, Greg

On Thu, 17 Jan 2019 at 23:15, m3047 <m3047 at m3047.net> wrote:

> Who cares about the RFC? In practice, SOME caching resolvers (and that's
> being charitable) WILL answer with TTL=0. I've had to live with PFSense
> deployments which did this.
> Which in turn leads to things like (for Mac users):
>    dscacheutil -flushcache
> Is that what you're talking about?
> On Thu, 17 Jan 2019, Greg Choules wrote:
> > [...]
> >
> > Is there ever a case, for cached answers, that the recursive server would
> > answer the client with TTL=0? Or would that be illegal? RFC1034 states
> that
> > records with TTL=0 "should not be cached". Note "should" and not "must".
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