[dns-operations] Questions on DNS Flag day 2020 proposal

Dave Lawrence tale at dd.org
Thu Jul 4 23:56:54 UTC 2019

Mark Andrews writes:
> Well RFC 1123 really fails to enumerate all the cases where TCP is
> necessary. 
> While it mentions RR too big it fails to mention referrals that are
> too big but they are just as important. Glue records are not
> optional.  Referrals should be setting TC=1 if glue does not fit.
> The same applies to priming query responses. 

I do not dispute this point whatsoever.

There were, however, authoritative operational environments that could
guarantee they would never, ever have a response of more than 512
bytes even when all necessary records were included.  They also didn't
do zone transfers.  It was in this sort of environment where it wasn't
completely unreasonable to not have TCP service per the wording of the
early DNS RFCs.

To be clear, I am not personally arguing in favour of optional TCP.  I
like that it was made mandatory.  I am only making an historical

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