[dns-operations] FlagDay 2020 UDP Size

[Paul Wouters]

On Tue, 4 Aug 2020, Viktor Dukhovni wrote:

> I've posted a few examples to this list of failure cases with a buffer
> size of 1232 that are resolved with buffer sizes of ~1400.
>
> So it is not entirely obvious where the most practical tradeoff lies.
> And indeed that best value likely depends on where the resolver (or auth
> server) sits on the network.  So while we may be able to converge on a
> recommended default, unfortunately some users may want/need to move the
> needle up or down to meet their needs.
>
> My sense at the moment is that 1232 is too conservative.  I see
> that (thanks Tony):
>
>    https://rp.delaat.net/2019-2020/p78/report.pdf
>
> recomments 1372 for IPv4 and 1332 for IPv6 on internal networks and 1232
> for stub resolvers using external IPv6 recursive servers out on the
> public Internet.

It's almoast as if 1) we shouldn't hardcode any of this and 2)
definately not switch behaviour on some arbitrary "flag day".

Paul