I see some of them show "h2" and some "http/2+quic/43" but never "h2+quic/43". What's the difference between h2 and http/2 in this case? And what's the "43" in "quic/43"? Protocol version or port number?
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Well basically QUIC is still being worked on and is not standardised. Google, as the inventors, have their own implementation (sometimes called gQUIC) which is only available in Chromium based browsers and on a few server implementations. It is based on HTTP/2 (well actually it was based on SPDY which then got standardised into HTTP/2).
It doesn't really use HTTP/2 any more but a modified version of it. So whether you call it h2 or http/2 doesn't really matter - it's neither. But at a high level h2 and http/2 can be treated the same in this context.
When QUIC is formally standardised later this year (or possibly even next year) by the IETF it will use HTTP/3 to reflect the diverges from HTTP/2 and so it should change to h3. That is currently being worked on but no browser supports it yet. It is known as iQUIC for now but imagine it will just become QUIC after it becomes a format standard and Google migrates to it and stops using gQUIC (in a similar way that the deprecated SDPY once HTTP/2 was formalised). gQUIC and iQUIC are already quite different.
The number 43 is a version number. Google used to iterate QUIC quite quickly as they were in charge of both ends (browser and server) though seems to have slowed down now (hopefully reflecting it's maturity and the fact less changes are needed). There used to be a change log in the Chromium source code showing what changed in each version, but can't find it now...
Barry Pollard
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