> On 21 Oct 2021, at 00:16, Paul Hoffman <[email protected]> wrote:
> 
> After reading the -06 somewhat carefully, I have only one question: why 
> should the DNS message ID be set to 0? If there's a good reason, is should be 
> listed in Section 5.2.1, but if there isn't, the requirement should be 
> removed. As the text indicates, this requirement makes forwarding more 
> difficult. It also makes a special case for a client implementation that can 
> do both DoQ and DoT.

Hi Paul,

The stream mapping of DoQ allows for unambiguous correlation or queries and 
responses so the the message ID isn’t needed. Using 0 means the number of 
outstanding queries on a DoQ connection isn’t limited to the Message ID space 
which would be an artificial limit inherited from DNS-over-UPD/TCP. It seems 
wrong to impose that on a transport specifically designed to multiplex, just to 
make proxying simpler.  Given that RFC8484 says "DoH clients ... SHOULD use a 
DNS ID of 0 in every DNS request.” that proxy problem already exists and isn’t 
unique to DoQ. 

It’s presence would also change the error condition from ‘what if the message 
ID isn’t 0’ to 'what happens if the response ID on a stream doesn’t match the 
query ID?’. It’s marginal but the former feels slightly cleaner.

However, we can certainly add text to clarify this - I’ve opened 
https://github.com/huitema/dnsoquic/issues/125

Sara. 

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