Re: [DNSOP] What is the purpose of NSEC3 "closest encloser" proofs?

[Shumon Huque <[e-mail]>]

Indeed Mark!

I should have thought about the general case, and not the specific example
in my mail. Thanks for correcting me! :)

Shumon.

On Thu, Oct 8, 2020 at 9:43 PM Mark Andrews <[e-mail]> wrote:

> Shumon, you where correct the first time.  A closest encloser can be a ENT
>
> a.b.c.d.example A ...
> a.e.x A ...
>
> with QNAME a.c.c.d.example the closest encloser is the ENT c.d.example.
>
> > On 9 Oct 2020, at 12:32, Shumon Huque <[e-mail]> wrote:
> >
> > On Thu, Oct 8, 2020 at 8:59 PM Shumon Huque <[e-mail]> wrote:
> > On Thu, Oct 8, 2020 at 7:46 PM Nick Johnson <nick=
> [e-mail]> wrote:
> > I'm reading RFC 5155, and I'm a bit puzzled by the requirement for
> "closest encloser" proofs to prove nonexistence of a domain. Given that the
> RFC requires generating NSEC3 records on empty non-terminals, isn't it
> sufficient to examine a single NSEC3 record to prove nonexistence?
> >
> > For example, if I want to prove the nonexistence of a.b.c.example, isn't
> it sufficient to validate an NSEC3 record that covers that name and is one
> level higher (eg, somehash.b.c.example)? Why do I need to prove the
> closest-encloser with a second NSEC3 record?
> >
> > -Nick Johnson
> >
> > The closest encloser proof actually *is* what proves that the name
> doesn't exist. But the other reason is that for NXDOMAIN proofs, you also
> need to prove that the name could not have been synthesized by a wildcard.
> The hypothetical wildcard that might have synthesized a response for the
> name is constructed by prepending the asterisk label to the closest
> encloser.
> >
> > Let's use your example and say 'a.b.c.example' doesn't exist in the zone
> example.
> >
> > Let's also say the longest ancestor of this name that actually does
> exist in the zone is 'c.example' (which could be an empty non-terminal or
> not -- either way, it will have an NSEC3 record matching the hash of the
> name).
> >
> > One small correction to my sentence above: strike the phrase about empty
> non-terminals - the closest encloser can't be an ENT of course (otherwise
> it wouldn't exist either!).
> >
> > Shumon.
> >
> > The NXDOMAIN proof consists of:
> >
> > ### Closest Encloser proof:
> > * the NSEC3 RR that matches the closest encloser name 'c.example'
> > * the NSEC3 RR that covers the next closer name 'b.c.example'
> >
> > This proves that b.c.example does not exist. This automatically means
> that all names under it, including a.b.c.example, do not exist.
> >
> > ### Wildcard non existence proof:
> > * the NSEC3 RR that covers the wildcard at the closest encloser, namely
> '*.c.example'.
> >
> > Shumon Huque
> >
> > _______________________________________________
> > DNSOP mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/dnsop
>
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: [phone]              INTERNET: [e-mail]
>
>