See which protocols are negotiated via ALPN (h2, http/1.1).
The ALPN Protocol Inspector shows which application-layer protocol was negotiated over TLS via ALPN (Application-Layer Protocol Negotiation). During the TLS handshake, client and server exchange a list of supported protocols (e.g. h2 for HTTP/2, http/1.1 for HTTP/1.1); the inspector reports the negotiated result. Use it to confirm a host speaks HTTP/2, to debug protocol mismatch, or to verify that your server advertises and selects the intended protocol. ALPN is the standard way to choose HTTP/2 vs HTTP/1.1 on the same port.
Extension in the TLS handshake that lets client and server agree on the application protocol (e.g. h2, http/1.1).
To select HTTP/2 or HTTP/1.1 on the same port without an extra round-trip; avoids protocol confusion.
Common ones: h2 (HTTP/2), http/1.1, and optionally others like grpc; the inspector shows what was chosen.
Server may default to HTTP/1.1 or use NPN (deprecated); ALPN is the standard for TLS.
Client sends preferred protocols; server picks one. Ensure server supports and advertises h2.