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

Paul Hoffman <paul.hoffman@icann.org> Thu, 07 June 2018 13:40 UTC

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From: Paul Hoffman <paul.hoffman@icann.org>
To: Tony Finch <dot@dotat.at>
CC: DoH WG <doh@ietf.org>
Thread-Topic: [Doh] [Ext] DNS Camel thoughts: TC and message size
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Date: Thu, 07 Jun 2018 13:40:29 +0000
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Subject: Re: [Doh] [Ext] DNS Camel thoughts: TC and message size
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On Jun 7, 2018, at 3:33 AM, Tony Finch <dot@dotat.at> wrote:
> 
> Paul Hoffman <paul.hoffman@icann.org> wrote:
>> 
>> DNS-over-TCP is defined in RFC 1035 and significantly updated in RFC
>> 7766. Unless I'm missing something, neither of those document support
>> the 65535 length restriction;
> 
> The restriction comes from the 2 octet message length field, RFC 1035
> section 4.2.2.

Ow! (I just slammed my forehead into the desk because this should have been obvious to me.)

Tony is completely correct here. DNS messages have well-defined length limits: 512-or-more-depending if carried over UDP, and 65535 if carried over TCP.

Bert's proposal is fine with me. The fact that RFC 7766 didn't mention this limitation doesn't change anything.

> EDNS buffer sizes need to be handled the samee as for TCP as well.

RFC 6891 says that the payload size is for transport over UDP, not TCP. What change are you requesting here?

--Paul Hoffman