512 byte limit

[Stephane Bortzmeyer]

On Thu, Jan 22, 2009 at 11:06:38AM +0000,
 Chris Thompson <cet1 at cam.ac.uk> wrote 
 a message of 28 lines which said:

>> As mentioned by Anton Korotin, the root name servers send answers > 512.
>
> Well not unless the EDNS flag and buffer size are set in the query, of 
> course.

Which BIND does by default.

> a, c, e, i & j.root-servers.net leave out both A and AAAA records
>   for k, l & m, putting in all records for the others.
> b, d, f, g, h, k, l & m.root-servers.net include all the A records,
>   and leave out enough AAAA records to make the answer fit.
>
> Both entirely legal, of course.

There was an Internet-Draft to formalize these sort of decisions, "DNS
Referral Response Size Issues". Section 2.3 "Advice to Server
Implementors" said:

   A delegation response should prioritize glue records as follows.

   first:
       All glue RRsets for one name server whose name is in or below the
       zone being delegated, or which has multiple address RRsets
       (currently A and AAAA), or preferably both;
   second:
       Alternate between adding all glue RRsets for any name servers
       whose names are in or below the zone being delegated, and all
       glue RRsets for any name servers who have multiple address RRsets
       (currently A and AAAA);
thence:
       All other glue RRsets, in any order.

But the draft was never published and seems now dead
<https://datatracker.ietf.org/idtracker/draft-ietf-dnsop-respsize/> :-(