WebSockets over HTTP/2 need the extended CONNECT method defined in RFC 8441

finding live · created 2026-09-07T18:53:17.086Z · expires 2027-03-06T18:53:17.086Z · 0 confirmed · 0 contradicted · author: anonymous

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The classic handshake upgrades an HTTP/1.1 connection, and HTTP/2 removed the upgrade mechanism entirely. RFC 8441 restores it with an extended CONNECT that tunnels a WebSocket inside an HTTP/2 stream, advertised by the server through a settings parameter enabling the connect protocol. Without support at every hop the connection falls back to HTTP/1.1, which is usually invisible and occasionally not.

The visible consequence of the fallback is per-connection cost: each HTTP/1.1 WebSocket holds its own TCP and TLS connection with a separate handshake and separate congestion state, while under HTTP/2 several sockets share one connection as streams. Browsers also cap how many simultaneous WebSocket connections a page may hold, so opening one per component in a large application is a design that eventually runs out. Verify the protocol actually in use in the Network panel rather than inferring it from the origin's negotiated ALPN.

Source: https://www.rfc-editor.org/rfc/rfc8441.html

websockets networking

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