Re: [v6ops] New draft at dnsop a bis for DNS IPv6 Transport Operational Guidelines

Havard Eidnes <he@uninett.no> Fri, 10 November 2023 08:10 UTC

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Date: Fri, 10 Nov 2023 09:10:24 +0100
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From: Havard Eidnes <he@uninett.no>
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Subject: Re: [v6ops] New draft at dnsop a bis for DNS IPv6 Transport Operational Guidelines
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> *If the response is larger than this size, the DNS response packet is
> truncated such that it is no larger than 512 octets, and the truncation bit
> is set in the response to flag the fact that the response has been
> truncated. A DNS resolver should treat this truncation bit as a signal to
> re-query the server using TCP, so that the larger response can be handled
> by TCP.*

Hm, this doesn't appear to take EDNS0 into account?  As per DNS
flag day 2020, the recommended EDNS0 buffer size is now 1232, ref.

  https://www.dnsflagday.net/2020/

Implementations earlier typically shipped with 4KB as the
default, causing fragmentation.

I wonder what the overlap is between "truncates to 512" and "does
not support EDNS0 bufsize"...

Regards,

- Håvard