[dns-operations] FlagDay 2020 UDP Size

Paul Wouters paul at nohats.ca
Tue Aug 4 21:50:22 UTC 2020

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".


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