Re: [Doh] How to start HTTP/2?

[Patrick McManus <[e-mail]>]

On Tue, Jan 16, 2018 at 10:02 AM, Stephane Bortzmeyer <[e-mail]>
wrote:

> RFC 7540 specifies several ways to start HTTP/2 over a TCP connection
> (section 3), such as upgrade from HTTP/1, or starting directly HTTP/2
> if you know the server accepts it. Which one should be used by DoH
> clients and servers? Section 7 of draft-ietf-doh-dns-over-https-02
> seems silent about it.
>
>
any valid 7540 mechanism is acceptable to DoH. however note that the
upgrade header specified by 3.2 of 7540 only applies to "http" schemed uris
and DoH requires "https" schemed uris. So as a practical matter you're
going to use ALPN with TLS though you would be allowed to use "prior
knowledge".. but if h2 is not a DoH MUST then the presence of DoH itself
doesn't constitute prior knowledge. (caching or configuration might
qualify).



> Note that this interacts with the discussion about whether HTTP/2
> support is SHOULD or MUST.
>
>
we reached consensus on that being SHOULD.. also its "h2 or its successors"
and I think that nit is important here..


> For the server:
>
> 1) accepts all RFC 7540 methods?
>

DoH doesn't constrain the server here. Indeed the server can serve more
than DoH simultaneously.


> 2) accepts only "immediately receives HTTP/2 frames"?
>
>
by which you mean ignore ALPN? That seems like a bad plan.



> For the client?
>
> 1) try all RFC 7540 methods? In which order?
> 2) try only "immediately sends HTTP/2 frames"? (If HTTP/2 support is a
> MUST, it makes sense)
>
>
again, I don't see a reason that DoH would particularly influence the
connection establishment choices.