Http2 is changed to http3 when refreshing site

hello.

now I’m using Cloudflare Pages. When I connect to https://lol-on-astro.devkr.info/cdn-cgi/trace first time, it appears like below

fl=34f204
h=lol-on-astro.devkr.info
ip=121.172.71.142
ts=1643883225.997
visit_scheme=https
uag=Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.81 Safari/537.36
colo=ICN
http=http/2
loc=KR
tls=TLSv1.3
sni=plaintext
warp=off
gateway=off

as you can see, http version is 2.

but when I refresh this URL, it appears like below

fl=34f116
h=lol-on-astro.devkr.info
ip=121.172.71.142
ts=1643883322.59
visit_scheme=https
uag=Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/98.0.4758.81 Safari/537.36
colo=ICN
http=http/3
loc=KR
tls=TLSv1.3
sni=plaintext
warp=off
gateway=off

as you can see, http version is 3.
http version transforms http 2 into http 3
why my http version is not 3 for the first connection?
thank you.

My slightly wild guess is browsers probably use HTTP/2 by default, but don’t know it’s an HTTP/3 site until it gets the HTTP/3 response header:
alt-svc: h3=":443"; ma=86400, h3-29=":443"; ma=86400

4 Likes

Thank you for your answer.

Currently I’m using [email protected] version that turns on flag Experimental QUIC protocol.
As I know, this flag enables http/3. So web browser has no problem I guess.
Anyway, thank you for your answer :grinning:

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