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WebTransport over HTTP/3: CORS, cross-origin datagrams, and bidirectional streams versus WebSocket
WebTransport uses custom TLS and ALPN negotiation—origin checks still apply before exposing streams to browsers.
1 min read
webtransporthttp3cors
Firewall
UDP port 443 must be open for QUIC—corporate networks may block WebTransport entirely.
MTU issues can fragment packets—separate from CORS but similar user-visible failure modes.
Game servers
Low-latency game code often mixes WebTransport with WebRTC—each path needs its own CORS or ICE policy docs.
Replay protection on datagrams must not rely on browser CORS alone.