Re: [DNSOP] why no QDCOUNT>1

Also with IQUERY (obsolete) you could get multiple QNAMEs in the response.

> On 22 Jul 2019, at 3:29 am, Paul Vixie <paul@redbarn.org> wrote:
> 
> someone here recently asked why multiple questions are allowed by the DNS 
> header format but not implemented. this was in the context of performance 
> comparisons between tcp/53 and udp/53, vs. DoT, vs. DoH.
> 
> the reason it's not implemented is that there's only one RCODE in the 
> response, so if one question results in RCODE=0 but another is RCODE=3, there 
> is no way to signal this. there's a similar issue with AA. and if there's a 
> delegation response for one but not the other, and one is the parent of the 
> other, ambiguity runs rampant.
> 
> the reason this hasn't been repaired via a massive protocol overhaul is that 
> it's a trivial matter to pipeline multiple questions, either on udp/53, DoT, 
> or even DoH. the extra DNS headers cost ten (10) octets per question, which is 
> insignificant.
> 
> here's some undocumented advice: don't initiate transactions via UDP/53 back 
> to back, because this microburst will probably overflow a queue somewhere. if 
> pipelining, either use DoT, or make sure there's a small delay between 
> subsequent UDP/53 transactions. 1.5 milliseconds is enough.
> 
> -- 
> Paul
> 
> 
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Mark Andrews, ISC
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