QUIC and HTTP/3 Reach IETF Last Call
QUIC is a new Internet transport protocol designed for secure, reliable, and multiplexed communications. HTTP/3 builds on top of QUIC, using the protocol's new features to solve performance problems such as Head-of-Line blocking, which helps web pages load faster, particularly on difficult networks.
QUIC and HTTP/3 are open standards that have been in development at the IETF for roughly four years. On October 21, 2020, after two rounds of Working Group Last Call, draft 32 of the document family describing both protocols entered IETF Last Call. This milestone signals to the broader IETF community that the working group considers the specifications nearly complete and is now soliciting final review and feedback.
The chairing of the Working Group changed hands earlier this year, and the shift comes at a critical juncture as the documents are shepherded through the final review phase. Protocol development at this stage happens on two parallel tracks: refining the specification documents themselves, and implementing, deploying, and testing libraries and clients. These efforts work together to meet the goals set in the group's charter. IETF Last Call is the point where the group and its responsible Area Director believe the technical work is essentially finished, and the focus now shifts to gathering input from the wider IETF community. Once the Last Call period concludes, stakeholders will assess the feedback, make any necessary adjustments, and hopefully move toward requesting publication as RFCs on the Standards Track.
Specification Maturity vs. Deployment Reality
The specification and implementation efforts often proceed at different rates, which is expected. The QUIC specification has been stable and deployable for some time, and HTTP/3 has been generally available on Cloudflare's edge infrastructure since September 2019, with support rolling out across browsers and tools including Chrome, Firefox, Safari, and curl. While draft 32 represents the latest specification, the broader community has standardized on draft 29 as a solid foundation for interoperability. This is typical as the protocol's foundational elements solidify and the scope of changes between iterations narrows. For most users, there is little practical difference between draft 29 and draft 32.
Currently, a visit to an HTTP/3-enabled site such as https://cloudflare-quic.com will show response headers containing Alt-Svc: h3-29="… — the draft version number is part of the advertisement. Once Last Call finishes and the RFCs are published, sites will begin offering Alt-Svc: h3="… without the draft suffix.
What Comes After QUIC v1
Entering Last Call does not mean the work on QUIC is done. QUIC v1 comprises the documents now in Last Call, but the protocol's extensibility opens the door to substantial future innovation. Expect continued work on multipath support, alternative congestion control approaches, and new methods for unreliable data delivery, such as the DATAGRAM frame.
The protocol is also being adapted for use cases beyond HTTP. Mapping DNS to QUIC, for instance, is a direct way to extend the protocol's benefits to new applications. The MASQUE Working Group has formed to explore using QUIC as a substrate for carrying other transport protocols, while the WebTransport Working Group is investigating QUIC and HTTP/3 as a foundation for a "supercharged WebSocket." The extensibility built into the protocol ensures that the current milestone is only the beginning.
