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

Havard Eidnes <> 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 <>
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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.

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"...


- Håvard