Interaction of CNAME and A records with regard to TTL

[Kross Joachim ICM N PG U ID A 1]

Hi all,

I am wondering about the following scenario:

A name server receives a request for an A record and tries to resolve it. It
finds a CNAME record with multiple A records attached. I assume it puts all
those records into its cache. Now, all those records have different TTLs. At
some point in time, when some of the A records have already expired, another
query for the original A record comes in. The CNAME record and some of the
related A records are still in the cache of the name server. What is the
behavior of the name server: does it return the CNAME record and the A
records it still has, i.e. an incomplete set with regard to all the
applicable records that exist, or does it forward the CNAME request to make
sure it has all the related A records?

I guess this is not applicable only to CNAME and A records, just A records
would pose the same question: If there are multiple A records for a domain
name, with different TTLs, what does a name server do if it receives a query
for that domain name after some of the records have expired: return the
incomplete list, or complete the list before returning it?

Does this possibly have something to do with the authoritative nameserver
portion of DNS responses?

Thanks!

Best regards,
Joachim