HTTP/3 not working in v3.0.0-rc5

[PeterDraex]

Hi!
I have enabled HTTP/3 on my entrypoint:
- "--entrypoints.websecure.http3"

And I have opened both TCP and UDP ports in the docker compose:
ports:

      - 80:80/tcp
      - 80:80/udp
      - 443:443/tcp
      - 443:443/udp

When I test it, I see that the response headers contain:

Alt-Svc: h3=":443"; ma=2592000

But the connection is not happening over HTTP/3 in any of my tested methods:

• Chrome Developer Tools shows h2 in the Protocol column of the Network tab
• Curl returns curl: (28) Failed to connect when used with --http3-only option, otherwise returns HTTP/2 200
• all of the online tests report QUIC connection could not be established or a similar error message

I'm using v3.0.0-rc5.

What can be causing this issue?
Thanks!

---

The curl command I used to test the host is:
docker run --network="host" ymuski/curl-http3 curl --insecure --head --http3-only https://example.com

[PeterDraex]

The issue was that a cloud firewall was blocking UDP connections to port 443.
It's working okay now.