Network services

ALPN

Also called Application-Layer Protocol Negotiation, h2, http/1.1

The TLS extension in which client and server agree on the protocol to speak inside, such as h2 or http/1.1.

The ClientHello lists the protocols the client speaks (h2, http/1.1; h3 inside QUIC) and the server answers with its pick, so the first application byte is already in the right protocol. curl -v shows ALPN: server accepted h2; a server that accepts only http/1.1 keeps every client on HTTP/1.1.

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