Re: [exim-dev] [Bug 2264] DNS lookups should not chase CNAME chains

[Viktor Dukhovni via Exim-dev]

> On Jun 9, 2018, at 7:17 PM, Jeremy Harris via Exim-dev <exim-dev@exim.org> 
> wrote:
> 
> It was:
> 
>  Zone:
>    cname.example. IN CNAME nomx.example.
>    nomx.example. IN A 192.0.2.1
>  Query:
>    cname.example. IN MX ?
>  Response:
>    Answers:
>      cname.example. IN CNAME nomx.example.

OK, that's what I'd expect, from this you can conclude
that "nomx.example" has no MX records.  No additional
query required.  You can then proceed to A/AAAA
queries for the final target...  Provided you
process *all* the CNAME records from the initial
response to re-construct the entire chain, and
make sure that the final chain element has no
associated MX RRs in the same answer (retry over
TCP if the answer is truncated).

In other words I don't yet see a need to do
"recursion" to chase the CNAME chain beyond
the nameservers initial reply...

-- 
        Viktor.


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