Enabled HTTP3 but it’s not working

I’ve enabled HTTP3 in the Cloudflare dashboard and tested my site, but it seems HTTP3 isn’t working for my site. When I check on https://http3check.net/ it says that quic is enabled but when I check on the network tab is still h2

If http3check says quic is enabled, then it probably is. What’s the site URL? And which browser are you using?

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Maybe your Web browser does not yet support HTTP/3? :slight_smile:

Do you have some HTTP headers like alt-svc h3 something (alt-svc h3-27=":443"; ma=86400, h3-28=":443"; ma=86400, h3-29=":443"; ma=86400)?

Yes it has, this is the exact header I see:

h3-27=":443"; ma=86400, h3-28=":443"; ma=86400, h3-29=":443"; ma=86400

Also I enabled the http3 in chrome//:flags and also tried it running it cmd.
Both resolved in h2

I actually have two sites,

squarecube.ml (this one has CF proxy )
h3.squarecube.ml (this one does not)

Both are OLS , and only the second one serves http3 content

Oddly enough, if I load sites in Firefox or Brave/Chrome, I can get H3 to show up the first time or two, but after a few refreshes, it falls back to H2. I just don’t know why. I haven’t done much testing since Cloudflare re-activated QUIC.

So the second link always says h3? and the first one sometimes it does on your end?
So is this a bug?

Using Google Canary browser with HTTP/3 enabled, that site works and connects via HTTP/3 H3-29 everytime for me

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What about the other one?

same works for HTTP/3 H3-29

using Canary with --enable-quic --quic-version=h3-29

with webpagetest and command line flag to force HTTP/3 on first request --enable-quic --origin-to-force-quic-on=squarecube.ml:443 --quic-version=h3-29


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I’ve never saw that on my end.
Is it because my browser doesn’t allow h3-29 by default? Does cloudflare only serves h3-29?

see https://developers.cloudflare.com/http3/chrome

Google supports HTTP/3 in Stable and Chrome Canary release channels. Canary channel builds are more regularly updated but may have some stability issues that you should keep in mind when testing. You can install both versions side-by-side; the Canary installer can be found hereOpen external link.

HTTP/3 is not enabled by default. Chrome must be launched with the --enable-quic --quic-version=h3-27 flags to work.

latest is h3-29 though CF works with h3-27, h3-28 and h3-29