QUIC (Quick UDP Internet Connections)
A UDP-based transport that fuses encryption and multiplexing, the foundation of HTTP/3.
QUIC (RFC 9000) is a transport-layer protocol built on UDP, originally designed by Google in 2012 and standardized by the IETF in 2021. Unlike TCP+TLS where encryption is layered on top, QUIC integrates TLS 1.3 directly into the transport — the handshake, key exchange, and encryption are part of the same protocol. It supports multiple independent streams over a single connection, eliminating the head-of-line blocking that has plagued HTTP/2 over TCP for a decade.
QUIC is the transport beneath HTTP/3, now used by Cloudflare, Google, Meta, and most large CDNs. Benefits for end users: 0-RTT resumption lets a returning client send data in the first packet, and connection migration lets a laptop switch from Wi-Fi to cellular without re-establishing. The cost: traditional middleboxes (load balancers, firewalls, deep packet inspectors) see only encrypted UDP — they cannot inspect beyond the initial handshake.
The GFW has variable behavior toward QUIC. Outbound QUIC to UDP 443 is generally allowed, but the SNI inside the QUIC handshake is still plaintext until ECH is widely deployed — so SNI-based blocking works against QUIC just as it works against TLS 1.2 TCP. For proxy services, routing QUIC requires a UDP-aware tunnel; a TCP-only proxy will silently drop QUIC connections and force a fallback to HTTP/2, slowing page loads.