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 _______________________________________________ DNSOP mailing list [email protected] https://www.ietf.org/mailman/listinfo/dnsop
