Re: [Doh] [Ext] DNS Camel thoughts: TC and message size

Ray Bellis <ray@bellis.me.uk> Thu, 07 June 2018 21:23 UTC

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From: Ray Bellis <ray@bellis.me.uk>
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Subject: Re: [Doh] [Ext] DNS Camel thoughts: TC and message size
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On 06/06/2018 23:42, Paul Hoffman wrote:
> I hear a lot of support for Bert's wording:
>    Specify that DNS messages carried over
>    DOH can be up to 65536 bytes large and note that truncation should be
>    handled as if the response was carried over TCP/53.

NB: that's up to but *not including* 65536.

UDP packets and TCP-framed DNS messages both have a 16 bit length field
with a maximum value of 65535.

In fact for UDP the actual DNS payload size is smaller, because that
65535 has to include the 8 byte UDP header.

Ray