HTTP/3 FAQ 2021-02-19 18:47:42 HTTP/3 frequently asked questions. This HTTP/3 FAQ tells you everything you've ever wanted to know about the HTTP/3 and QUIC application protocol.


Everything you need to know about the HTTP/3 and QUIC application and transfer protocols.

HTTP/3 Frequently Asked Questions
  • What are HTTP/3 and QUIC?

    • HTTP/3 is the newest version of the Hypertext Transfer Protocol, formerly referred to as "HTTP over QUIC," and is the successor to HTTP/2.

      QUIC was originally a Google effort to improve HTTP/2 by transporting it encrypted over UDP. In 2016, the IETF began working to standardize the protocol. Part of that process involved splitting QUIC into the transport protocol (QUIC) and the application protocol (HTTP/3).

      HTTP/3 is close to its final form. The IETF drafts are going through the last formalities before being published as RFCs.

  • What is the difference between HTTP/3 and HTTP/2?

    • The main difference is HTTP/3 uses QUIC, which is is built on UDP, while HTTP/2 uses TCP. In addition, HTTP/3 uses QPACK to compress headers, while HTTP/2 uses HPACK to compress headers.

  • Will HTTP/3 replace HTTP/2?

    • No. HTTP/2 and HTTP/3 work in a similar way, but HTTP/2 uses TCP, while HTTP/3 uses UDP-based QUIC as the transport protocol. HTTP/3 support is optional. When enabled, HTTP/3 can fall back to HTTP/2 or HTTPS if not available.

  • Is HTTP/3 faster than HTTP/2?

    • It depends.

      From the end-user-experience point of view: Yes! A user may feel that HTTP/3 is serving the site more fluently than HTTP/2. This is particularly true when the network conditions are less than optimal.

      From a cost-of-service point of view: No! HTTP/3 costs more CPU cycles to push the same amount of traffic as HTTP/2. Though, this cost is likely to shrink as operating systems optimize their UDP subsystems.

  • What is the difference between HTTP/3 and QUIC?

    • HTTP/3 is based on QUIC. QUIC was originally developed by Google, and the Google version of QUIC is now referred to as gQUIC. HTTP/3 has evolved from gQUIC with contributions from the IETF working group.

      HTTP/3 is the full application protocol. QUIC refers to the underlying transport protocol, which is not limited to serving HTTPS traffic.

  • How do you test if a website supports HTTP/3 or QUIC?

  • Why is HTTP/3 better than HTTP/2?

    • HTTP/3 uses QUIC, which reduces the Head of Line (HoL) blocking issue. All TCP-based protocols suffer from HoL blocking, including HTTP/2.

  • Why do HTTP/3 and QUIC matter?

    • HTTP/3, which uses QUIC as a transport layer, is a new, improved version of HTTP. Web infrastructure technology (web servers, web browsers, etc.) are being updated to support HTTP/3, and take advantage of HTTP/3's speed, reduced latency, better handling of packet errors, and built-in encryption.

  • How do you use HTTP/3?

    • To use HTTP/3 on your site, you require a web server that supports it. Alternately, you can use a content delivery network that supports HTTP/3 in front of your site.

      In order for your visitors to experience a full HTTP/3 connection, they need to access your site via a browser that supports HTTP/3.

  • Which browsers support HTTP/3?

    •   Google Chrome Canary, if launched with the --enable-quic and --quic-version=h3-29 command-line arguments
    •   Mozilla Firefox Nightly, via the network.http.http3.enabled preference in about:config.
    • More browser support is coming soon, and can be verified at Can I use...

  • Which web servers support HTTP/3?

    • LiteSpeed has been supporting QUIC since 2017. In July of 2019, LiteSpeed was the first to introduce web server support for HTTP/3 at a production grade and capacity. The LiteSpeed implementation of QUIC and HTTP/3 is stable, production ready, and available in the following products:

      •  LiteSpeed Enterprise Web Server
      •  LiteSpeed ADC
      •  OpenLiteSpeed

      Nginx support is currently in beta

      H2O, Apache Traffic Server, and hypercorn support HTTP/3 now, and more off-the-shelf server support should become available soon.

    • Which CDNs support HTTP/3?

      •   Cloudflare
      •   Fastly
      •   Akamai

      The new CDN features support for both older gQUIC and HTTP/3 . As the name implies, the CDN was designed specifically to take advantage of the benefits of HTTP/3 and QUIC. As you’d expect, serves content via HTTP/3 to visitors, but it also can communicate with a site’s backend via HTTP/3 and QUIC, making for a complete HTTP/3-powered connection.

LiteSpeed HTTP/3 solutions

HTTP/3 is available in LiteSpeed products across the board, with rock-solid stability and unbeatable performance.

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