thanks for this. can you propose new text? educating the authors to the
point where they can speak for your experience may be error prone.
re:
Vladimír Čunát wrote on 2023-01-28 09:42:
With Knot Resolver + Knot DNS the fragmentation issues are currently
being addressed quite simply:
* IP_PMTUDISC_OMIT to avoid spoofed MTU
* UDP size limit, 1232 by default (and of course honoring if the other
side wants lower, etc.)
Other points from the draft, perhaps less important:
* fragments are ignored if they arrive over an XDP interface (XDP
usage is not typical)
* TCP is attempted after repeated UDP timeouts
* minimal responses: yes (not configurable)
* smaller signatures: yes, ecdsap256sha256 by default
I also believe that the MTU spoofing should be reflected in this draft's
recommendations. With the current list I _suspect_ attackers could
relatively easily force all 512B+ answers to TC=1 + TCP (if on IPv4).
1232: I haven't gone in detail over the relevant measurements so I'm not
even 100% sure they're conclusive, but it might really will be better to
increase that default. I don't expect any other changes related to this
draft for future.
Use 'minimal-responses' configuration: Some implementations have a
'minimal responses' configuration that causes DNS servers to make
response packets smaller, containing only mandatory and required data
Nit: this formulation makes me wonder what this recommends for SVCB-like
records. Strictly taken I'd say it clashes with some SHOULDs from the
soon-to-be RFC. Either way, SVCB-like queries could be prone to
generating large answers (if this SHOULD is followed).
--Vladimir
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P Vixie
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