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I was just curious about the nomenclature of certain variables part of DNS's RFC: https://www.ietf.org/rfc/rfc1035.txt

While I was able to find most other acronyms :

  • AN in ANCOUNT seems stands for Answer
  • NS in NSCOUNT stands for Name Server
  • AR in ARCOUNT stands for Additional Record

I was wondering what does "QD" stand for in the "QDCOUNT"?

ooransoy
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Nicolas Bouvrette
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3 Answers3

9

it wasn't an acronym. QDCOUNT just means what it's defined to mean. FWIW, i always think of it as Query Domain Count, because the query section has no RDATA's in it unlike the other sections, each query has just a Name, Class, and Type.

note that this field is useless now, because BIND has always rejected QDCOUNT != 1. there is no way to ask more than one question per transaction, and it's not an oversight, rather it's because there is only one AA bit to describe the entire answer section.

Paul Vixie
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  • Hey Thanks Paul, I appreciate that you took the time to answer. Considering your background I trust that you got this from the source? I also noticed that the multi-question concept never got supported (probably for the sake of simplicity). I was really curious on the "QD" since all other fields were easy to link to their acronyms. – Nicolas Bouvrette Aug 30 '15 at 01:09
  • Far be it from me to say you are wrong, but I can't help but feel it stood for SOMETHING when it was picked. It could have been named XKJG612_BITZERO, but speaking as a programmer I know people usually pick things that make sense. Very cool you answered though :) – Drazisil Aug 30 '15 at 06:18
6

Based on https://tools.ietf.org/html/rfc2929 I believe it likely stands for Query Data, but I don't believe that you will get an official answer outside of asking the people who designed DNS.

The unsigned fields query count (QDCOUNT), answer count (ANCOUNT),
   authority count (NSCOUNT), and additional information count (ARCOUNT)
   express the number of records in each section for all opcodes except
   Update.  These fields have the same structure and data type for
   Update but are instead the counts for the zone (ZOCOUNT),
   prerequisite (PRCOUNT), update (UPCOUNT), and additional information
   (ARCOUNT) sections.

Other references: 1, 2

We could also just go with DNSRR iteration that says it means Query DNS Count. :)

Drazisil
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  • I already tried to ask Mockapetris directly but got no answers so far :) If anyone else has a better way to get in touch with IETF DNS experts I would be more than happy to try again. Good catch on the references. I agree with you that the "D" most likely stands for "Data" but still would like a more official confirmation. – Nicolas Bouvrette Aug 29 '15 at 12:37
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I think that the "rule" could be devised looking to the explanations in section 4.1.2 about the question section format, QD should be interpreted as Question Definition or better Query Definition, since every contained element is referred to as being a query.

abarisone
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