[dns-operations] FlagDay 2020 UDP Size

[Tony Finch]

Viktor Dukhovni <ietf-dane at dukhovni.org> wrote:

> What I haven't seen reported is measurements of problems that occur when
> the EDNS(0) UDP buffer size is *too small*.

A full service resolver should not have a fixed buffer size but instead
probe for what works. They pretty much already do so. There remains some
question about what their upper limit should be; it seems reasonable to me
to grow up to a 1500 octet MTU but no bigger.

Stub resolvers should do the same if they have enough brain to do so :-)

The tricky balance is the UDP response size limit on the auth side, which
can't be adaptive, and probably needs to be a bit more pessimistic than
a 1500 octet MTU.

Tony.
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