Interaction of CNAME and A records with regard to TTL

phn at phn at
Fri Jan 17 19:36:58 UTC 2003

Kross Joachim ICM N PG U ID A 1 <joachim.kross at> wrote:

> 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 =
> those records into its cache. Now, assume all those records have differe=
> TTLs. At some point in time, when some of the A records have already

This violates standards. A "record set" ( collection of records=20
with the same "key" MUST have identical TTL)

> expired, another query for the original A record comes in. The CNAME rec=
> and some of the related A records are still in the cache of the name ser=
> What is the behavior of the name server: does it return the CNAME record=
> the A records it still has, i.e. an incomplete set with regard to all th=
> applicable records that exist, or does it forward the CNAME request to m=
> sure it has all the related A records?

> I guess this is not applicable only to CNAME and A records, just A recor=
> would pose the same question: If there are multiple A records for a doma=
> name, with different TTLs, what does a name server do if it receives a q=
> 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 nameserve=
> portion of DNS responses?

> Thanks!

> Best regards,
> Joachim

Peter H=E5kanson=20=20=20=20=20=20=20=20=20
        IPSec  Sverige      ( At Gothenburg Riverside )
           Sorry about my e-mail address, but i'm trying to keep spam out,
	   remove "icke-reklam" if you feel for mailing me. Thanx.

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