glue records

[Kevin Darcy]

penszo at gmail.com wrote:
> Hi,
>
> I have a question regarding glue records.
>
> When I ask a name server which is (hypothetical) responsible
> for .space zone:
>
> [first query]
> dig @ns.for.space www.somedomain.space A
>
> I get answer like this:
>
> ;; QUESTION SECTION:
> ;www.somedomain.space.                        IN      A
>
> ;; AUTHORITY SECTION:
> somedomain.space.             86400   IN      NS
> ns1.somedomain.space.
> somedomain.space.             86400   IN      NS
> ns2.somedomain.space.
>
> ;; ADDITIONAL SECTION:
> ns1.somedomain.space.         86400   IN      A       1.2.3.4
> ns2.somedomain.space.         86400   IN      A       1.2.3.5
>
> I get name servers for somedomain.space domain with glue records in
> ADDITIONAL SECTION.
>
> My question is: As 'ADDITIONAL' section 'Carries RRs which may be
> helpful in using the RRs in the other sections' should or must be in
> responce from ns.for.space? What will happen if ns.for.space will not
> return ADDITIONAL SECTION with glue records? Is this RFC compliant?
>   
It's mandatory in that case to provide the A records in the Additional 
Section.
> Will resolvers handle such responce, quering for A record for
> ns1.somedomain.space or ns2.somedomain.space and getting responce like
> this:
>
> ns1.somedomain.space.         86400   IN      A       1.2.3.4
>
> and then quering ns1.somedomain.space for A record for www.somedomain.space?
>   
And where would that A record come from? From ns1.somedomain.space or 
ns2.somedomain.space? No-one would be able to get those A records, since 
they wouldn't be able to ask the authoritative nameservers for them, 
because they don't know the A records for those nameservers, and so on 
and so on and so on. It's a chicken-and-egg situation (see 
http://en.wikipedia.org/wiki/Chicken_and_egg, although 
http://en.wikipedia.org/wiki/Circular_cause_and_consequence is more 
technically accurate). That's why the glue records in the Additional 
Section are mandatory in this case.
> Does it matter that A record for ns1.somedomain.space is returning in
> ADDITIONAL or ANSWER SECTION?
>   
If the query type is A, then the A record(s) which answer(s) the query 
should be in the Answer Section of the response. The only A records 
which would appear in the Additional Section would be those "associated" 
with the answer, but not directly answering it, such as (optionally) the 
A records of the NS records which (optionally) appear in the Authority 
Section, assuming that those A records don't duplicate what's in the 
Answer Section (there's a "no duplication" rule in RFC 2181, see section 
5.5).

                                                                         
                                    - Kevin