Re: DNS: Order of CNAME and A in Authoritative Reply.

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Hi Viktor,

> > How do we get the desired behaviour clarified so implementers of
> > servers and clients have a reference when trying to resolve their
> > disagreement?  IMO, the CNAME should precede the A, but that still
> > isn't precise enough.  Some are asking if it's sufficient that all
> > CNAME precede all A.
>
> Which clients that are not recursive resolvers talk directly to
> authoritative nameservers (not counting "nslookup", "dig", ...)?

Those, like ping, where a foo.local is provided by a local,
authoritative, nameserver.  DNS is increasing being used on a local
level, e.g. as a distributed key/value lookup.  That's one reason why
new servers are coming along and meeting old clients.

> If an order is to be specified, then it should not only order all
> applicable CNAME RRs before any records that bear the final anwer, but
> also order the CNAME records in a chain of CNAMEs, so that the source
> CNAME precedes the target CNAME:

I agree.  That would seem to give the simplest client implementation,
and probably matches early BIND.

> However, it is not clear why the order of records in a non-recursive
> response needs to be constrained in any way.  Surely, recursive
> resolvers can reorder the records as necessary?

I have a lack of DNS Fu.  If the recursive resolver looking up (A?
foo.local) talked to the authoratitive server that answered (A
bar.local=1, CNAME foo.local=bar.local) then, assuming it understood
that completely answered the question, might it not simply copy the
answer back to the client without re-ordering?

Cheers, Ralph.




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