[dns-operations] extra records in resolver answer, any benefit?

Paul Vixie paul at redbarn.org
Wed Jan 28 01:10:13 UTC 2015

> Olafur Gudmundsson <mailto:ogud at ogud.com>
> Tuesday, January 27, 2015 1:22 PM
> The original reasoning was to save round trip times and network
> bandwidth.
> This does not hold any more as Dan Kaminsky showed us how to use extra
> data as
> cache poison via forged answers.
> In DNS referrals there is value for extra data when name servers are
> below the zone cut.
> In no other situation do I see value for application to see anything
> that is not
> in the first NON-empty response section. (i.e. either Answer or,
> Authority)
> I have been thinking about shortening MX answers by only include the
> Answer section and
> violate the server side processing of additional records. If Florian
> and Tony are right then that should be harmless. As in most cases
> these days mail servers are outside the domain.

i'm fine with additional data that's within the bailiwick of a referral,
but also, with data whose owner name matches the qname. so, including
AAAA as additional data for QTYPE=A, and including A as additional data
for QTYPE=AAAA, has no "kaminsky problem", and could save round trips.

note, it has to match the QNAME, not the final owner of a CNAME chain,
to qualify for this treatment.

Paul Vixie
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