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Re: [Doh] No truncation for DNS over HTTPS

Ray Bellis <ray@bellis.me.uk> Thu, 22 March 2018 10:24 UTC

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From: Ray Bellis <ray@bellis.me.uk>
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Subject: Re: [Doh] No truncation for DNS over HTTPS
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On 22/03/2018 09:20, Davey Song wrote:

> Although the dns-udpwireformat MIME type was defined, the dns wireformat
> data should not be treated as a datagram encapsulted in a HTTPs header
> but a new byte stream over HTTPs (similar with DNS TCP usage). No
> truncation loop is needed. Peopole may take it for granted, but It
> should be explicitely mentioned in this draft.   

If the DNS API Server is proxying between DOH and a real UDP DNS server
then the UDP DNS server might still set the TC bit and the proxy could
return that, so the client may still have to cope with +TC.

The alternative is that the proxy has to have sufficient smarts to
recognise the returned +TC and re-issue the request over TCP to the
backend DNS server.

Ray

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