Re: [DNSOP] [Doh] [EXTERNAL] Re: New I-D: draft-reid-doh-operator

Ted Lemon <mellon@fugue.com> Mon, 25 March 2019 16:23 UTC

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From: Ted Lemon <mellon@fugue.com>
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Date: Mon, 25 Mar 2019 17:23:17 +0100
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To: Tony Finch <dot@dotat.at>
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Subject: Re: [DNSOP] [Doh] [EXTERNAL] Re: New I-D: draft-reid-doh-operator
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It seems like SACK would make the problem less bad in theory, but wouldn’t eliminate the problem.   With DNS-over-DTLS, if a packet is lost, the next packet still gets an immediate answer, because DTLS is a datagram protocol, not a stream protocol.   The retry strategy for DNS-over-DTLS would be the same as DNS-over-UDP, once the Diffie-Hellman shared key has been derived.   So assuming you are using this to communicate to a resolver, there would be an initial handshake that’s extra compared to DNS-over-UDP, and then it would just be DNS-over-UDP until such time as re-keying is needed.

> On Mar 25, 2019, at 5:13 PM, Tony Finch <dot@dotat.at>; wrote:
> 
> Ted Lemon <mellon@fugue.com>; wrote:
>> On Mar 25, 2019, at 4:04 PM, Tony Finch <dot@dotat.at>; wrote:
>>> If I understand it correctly, DTLS leaves MTU and fragmentation up to the
>>> application protocol. The DNS has horrible packet size problems, so it
>>> needs a lot more help than DTLS provides. QUIC is much better.
>> 
>> Indeed.  My point was simply that this avoids ordering problems, just as
>> QUIC does.  I suspect that it is worth having DNS-over-DTLS; QUIC is
>> great, but based on what I’ve been seeing, quite a lot, and probably not
>> appropriate for a lot of use cases where DNS-over-DTLS would do just
>> fine.
> 
> It isn't so much ordering that is the problem, but not delaying answer B
> when answer A suffers packet loss. I'm kind of curious about what the
> relative trade-offs might be between DoQ and DoT with a decent SACK
> implementation, when there is not much latency between the client and the
> resolver. DNS-over-DTLS will need its own application layer retry
> strategy. I kind of prefer the idea of DNS being able to re-use a good
> off-the-shelf transport protocol rather than doing its own thing.
> 
> Tony.
> -- 
> f.anthony.n.finch  <dot@dotat.at>;  http://dotat.at/
> Irish Sea: West or northwest 4 or 5. Smooth or slight. Showers. Good.