> I mean even if there is no "Happy Eyeballs", it would still work for end users, > no?
No browsers and other clients prefer IPv6 and there would be a rather long timeout till the client falls back and tries IPv4. If it falls back.
> So why would it work sometimes if IPv6 is consistently broken and IPv4 is not?
> (I'm not saying it won't happen; just that it shouldn't be "caused by HE" -- HE > literally is the solution to this issue in general as the author said
> themselves!)
IPv6 wasn't broken. For HE, an HTTP 403 is a valid connection. TCP handshake works, IPv6 works.
I had another case where the TCP handshake worked, and the browser decided to use IPv6 is good, but then came the TLS handshake, and it failed because PMTUD (Path MTU Discovery) was broken.