[dns-operations] FlagDay 2020 UDP Size

Petr Špaček petr.spacek at nic.cz
Tue Aug 4 10:59:37 UTC 2020

On 03. 08. 20 19:20, jack tavares wrote:
> I am asking for a clarification on the recommended default settings for Resolvers etc.
> I understand that the default setting should be 1232.
> But what is not clearly laid out, in my opinion, is if;
> a client sends a larger EDNS buffer size, what should the resolver do?
> Currently the resolvers i work with have a max of 4096 by default, and will respect a LOWER limit
> from a client, but cap the response at 4k.
> Is it ok to go higher, if we set the default at 4k?

Resulting answer will usually have max size computed as minimum from (client, server) advertised buffer size.

Whole point of DNS flag day 2020 is to go to smaller values to make UDP over the wild Internet more reliable.

Is there a particular section of https://dnsflagday.net/2020/ which is confusing?

Petr Špaček  @  CZ.NIC

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