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

[Mark Andrews <[e-mail]>]

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a.b.c.d.example A …
a.e.c.d.example A … 

with QNAME a.c.c.d.example the closest encloser is the ENT c.d.example.

> On 9 Oct 2020, at 12:43, 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
>> 
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> 
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> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: [phone]              INTERNET: [e-mail]