Re: 426 Upgrade: HTTP/3.0

It is just confusing because the context is missing. The latter paragraphs are about upgrading the connection with 101, whereas the 426 response (and in general for any response other than 101) the Upgrade header field is listing all protocols supported by the server, not just those available via request Upgrade.

Yes, it could be explained better after the addition of 426, but I think we are well beyond the stage of editorial clarification. A blog post would do.

....Roy


> On Jul 7, 2025, at 1:14 AM, Jan Schaumann <jschauma@netmeister.org> wrote:
> 
> Hi,
> 
> I just noticed that RFC9110 says in section 15.5.22
> https://httpwg.org/specs/rfc9110.html#status.426
> 
> "Example:
> 
> HTTP/1.1 426 Upgrade Required
> Upgrade: HTTP/3.0
> "
> 
> Seeking an upgrade to H3 would entail a switch in
> connection protocol, but further down in section 7.8,
> RFC9110 also explicitly says
> 
> "The Upgrade header field only applies to switching
> protocols on top of the existing connection; it cannot
> be used to switch the underlying connection
> (transport) protocol, nor to switch the existing
> communication to a different connection. For those
> purposes, it is more appropriate to use a 3xx
> (Redirection) response (Section 15.4)."
> 
> 
> So these two parts seem to contradict each other, and
> the 'Upgrade' section should use a different example?
> 
> -Jan
> 
> 

Received on Wednesday, 9 July 2025 17:45:30 UTC