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HTTP/2 (originally named HTTP/2.0) is the second major version of the HTTP network protocol used by the World Wide Web. It is based on SPDY.[1] HTTP/2[2] was developed by the Hypertext Transfer Protocol working group (httpbis, where bis means "repeat" or "twice") of the Internet Engineering Task Force.[3] HTTP/2 is the first new version of HTTP since HTTP 1.1, which was standardized in RFC 2068 in 1997. The Working Group presented HTTP/2 to IESG for consideration as a Proposed Standard in December 2014,[4][5] and IESG approved it to publish as Proposed Standard on February 17, 2015.[6][7] The HTTP/2 specification was published as RFC 7540 in May 2015.[8]

The standardization effort was supported by Chrome, Opera, Firefox, Internet Explorer 11, Safari, Amazon Silk and Edge browsers.[9] Most major browsers added HTTP/2 support by the end of 2015.

According to W3Techs, as of November 2015 2.3% of the top 10 million websites supported HTTP/2.[10]


The working group charter mentions several goals and issues of concern:[3]

Differences from HTTP 1.1[edit]

The proposed changes do not require any changes to how existing web applications work, but new applications can take advantage of new features for increased speed.[11]

HTTP/2 leaves most of HTTP 1.1's high level syntax, such as methods, status codes, header fields, and URIs, the same. The element that is modified is how the data is framed and transported between the client and the server.[11]

Websites that are efficient minimize the number of requests required to render an entire page by minifying (reducing the amount of code and packing smaller pieces of code into bundles, without reducing its ability to function) resources such as images and scripts. However, minification is not necessarily convenient nor efficient, and may still require separate HTTP connections to get the page and the minified resources. HTTP/2 allows the server to "push" content, that is, to respond with data for more queries than the client requested. This allows the server to supply data it knows a web browser will need to render a web page, without waiting for the browser to examine the first response, and without the overhead of an additional request cycle.[12]

Additional performance improvements in the first draft of HTTP/2 (which was a copy of SPDY) come from multiplexing of requests and responses to avoid the head-of-line blocking problem in HTTP 1 (even when HTTP pipelining is used), header compression, and prioritization of requests.[13]

Genesis in and later differences from SPDY[edit]

SPDY (pronounced like "speedy") is a previous HTTP-replacement protocol developed by a research project spearheaded by Google.[14] SPDY primarily focuses on reducing latency. SPDY uses the same TCP pipe but different protocols to accomplish this reduction. The basic changes made to HTTP 1.1 to create SPDY include: "true request pipelining without FIFO restrictions, message framing mechanism to simplify client and server development, mandatory compression (including headers), priority scheduling, and even bi-directional communication".[15]

The httpbis working group considered Google's SPDY protocol, Microsoft's HTTP Speed+Mobility proposal (SPDY based),[14] and Network-Friendly HTTP Upgrade.[16] In July 2012 Facebook provided feedback on each of the proposals and recommended HTTP/2 be based on SPDY.[17] The initial draft of HTTP/2 was published in November 2012 and was based on a straight copy of SPDY.[18]

The biggest difference between HTTP/1.1 and SPDY, is that each user action in SPDY is given a "stream ID", meaning there is a single TCP channel connecting the user to the server. SPDY splits requests into either control or data, which is a "simple to parse binary protocol with two types of frames."[15] SPDY has shown evident improvement from HTTP, with a new page load speedup ranging from 11.81% to 47.7%.[19]

The development of HTTP/2 used SPDY as a jumping-off point. Among the many detailed differences between the protocol, the most notable is that HTTP/2 uses a fixed Huffman code-based header compression algorithm, instead of SPDY's dynamic stream-based compression. This helps to reduce the potential for compression oracle attacks on the protocol, such as the CRIME attack.

On February 9, 2015, Google announced plans to remove support for SPDY in Chrome by early 2016, in favor of support for HTTP/2, starting with Chrome 40.[20]


HTTP/2 is defined for both HTTP URIs (i.e. without encryption) and for HTTPS URIs (over TLS, where TLS 1.2 or newer is required).[21]

Although the standard itself does not require usage of encryption,[22] most client implementations (Firefox,[23] Chrome, Safari, Opera, IE, Edge) have stated that they will only support HTTP/2 over TLS, which makes encryption de facto mandatory.[24]


HTTP/2's development process and the protocol itself have faced criticism.

The FreeBSD and Varnish developer Poul-Henning Kamp claims that the standard was prepared on an unrealistically short schedule, ruling out any basis for the new HTTP/2 other than the SPDY protocol and resulted in missing other opportunities for improvements.[25] Kamp criticizes the protocol itself for being inconsistent and having needless, overwhelming complexity.[25] He also states that the protocol violates the protocol layering principle,[25] for example by duplicating flow control with transport layer (TCP). Most concerns, however, have been related to encryption issues.


Initially, some members of the Working Group were trying to push an encryption requirement into the protocol. This faced criticism.

Critics stated that encryption has non-negligible computing costs (though available data shows the opposite[26]) and that many HTTP applications have actually no need for encryption and their providers have no desire to spend additional resources on it. Poul-Henning Kamp, lead developer of varnish HTTP accelerator and a senior FreeBSD kernel developer, has criticised IETF for following a particular political agenda with HTTP/2.[25][27][28] The criticism of the agenda of mandatory encryption within the existing certificate framework is not new, nor is it unique to members of the open-source community – a Cisco employee stated in 2013 that the present certificate model is not compatible with small devices like routers, because the present model requires not only annual enrollment and remission of non-trivial fees for each certificate, but must be continually repeated on an annual basis.[29] Working Group finally did not reach consensus over the mandatory encryption,[22] although most client implementations require it, which makes encryption a de facto requirement.

The HTTP/2 protocol also faced criticism for not supporting opportunistic encryption, a measure against passive monitoring similar to the STARTTLS mechanism that has long been available in other internet protocols like SMTP. It has been pointed out that the HTTP/2 proposal goes in violation of IETF's own RFC7258 "Pervasive Monitoring Is an Attack", which also has a status of Best Current Practice 188.[30] RFC7258/BCP188 mandates that passive monitoring be considered as an attack, and protocols designed by IETF should take steps to protect against passive monitoring (for example, through the use of opportunistic encryption). A number of specifications for opportunistic encryption of HTTP/2 have been provided,[31][32][33] of which draft-ietf-httpbis-http2-encryption-01 is an official work item of the working group.

Development milestones[edit]

Status Date Milestone[3]
Done December 20, 2007[34][35] First HTTP 1.1 Revision Internet Draft
Done January 23, 2008[36] First HTTP Security Properties Internet Draft
Done Early 2012[37] Call for Proposals for HTTP 2.0
Done October 14 – November 25, 2012[38][39] Working Group Last Call for HTTP 1.1 Revision
Done November 28, 2012[40][41] First WG draft of HTTP 2.0, based upon draft-mbelshe-httpbis-spdy-00
Held/Eliminated Working Group Last Call for HTTP Security Properties
Done September 2013[42][43] Submit HTTP 1.1 Revision to IESG for consideration as a Proposed Standard
Done February 12, 2014[44] IESG approved HTTP 1.1 Revision to publish as a Proposed Standard
Done June 6, 2014[34][45] Publish HTTP 1.1 Revision as RFC 7230, 7231, 7232, 7233, 7234, 7235
Done August 1, 2014 – September 1, 2014[5][46] Working Group Last call for HTTP/2
Done December 16, 2014[4] Submit HTTP/2 to IESG for consideration as a Proposed Standard
Done December 31, 2014 – January 14, 2015[47] IETF Last Call for HTTP/2
Done January 22, 2015[48] IESG telechat to review HTTP/2 as Proposed Standard
Done February 17, 2015[6] IESG approved HTTP/2 to publish as Proposed Standard
Done May 14, 2015[49] Publish HTTP/2 as RFC 7540

HTTP/HTTPS servers[edit]

Not planned
  • lighttpd has no support for SPDY or HTTP/2 planned in version 1.x[65]

See also[edit]


  1. ^ Bright, Peter (Feb 18, 2015). "HTTP/2 finished, coming to browsers within weeks". Ars Technica. 
  2. ^ Thomson, M. (ed. ), Belshe M. and R. Peon. "Hypertext Transfer Protocol version 2 - draft-ietf-httpbis-http2-16". HTTPbis Working Group. Retrieved February 11, 2015. 
  3. ^ a b c "Hypertext Transfer Protocol Bis (httpbis) - Charter". Internet Engineering Task Force. 2012. 
  4. ^ a b "History for draft-ietf-httpbis-http2-16". IETF. Retrieved 2015-01-03. 2014-12-16 IESG state changed to Publication Requested 
  5. ^ a b Raymor, Brian (August 7, 2014). "Wait for it – HTTP/2 begins Working Group Last Call!". Microsoft Open Technologies. Retrieved 2014-09-07. 
  6. ^ a b The IESG (February 17, 2015). "Protocol Action: 'Hypertext Transfer Protocol version 2' to Proposed Standard (draft-ietf-httpbis-http2-17.txt)". httpbis (Mailing list). Retrieved February 18, 2015. 
  7. ^ Mark Nottingham (February 18, 2015). "HTTP/2 Approved". Internet Engineering Task Force. Retrieved March 8, 2015. 
  8. ^ "RFC 7540 - Hypertext Transfer Protocol Version 2 (HTTP/2)". IETF. May 2015. Retrieved May 14, 2015. 
  9. ^ "Can the rise of SPDY threaten HTTP?". Restlet, Inc. October 2011. 
  10. ^ "Usage of HTTP/2 for websites". W3Techs. November 2015. 
  11. ^ a b Ilya Grigorik. "Chapter 12: HTTP 2.0". High Performance Browser Networking. O'Reilly Media, Inc. Retrieved March 19, 2014. 
  12. ^ Pratt, Michael. "Apiux". Retrieved March 19, 2014. 
  13. ^ Dio Synodinos (November 2012). "HTTP 2.0 First Draft Published". (C4Media Inc.). 
  14. ^ a b Sebastian Anthony (March 28, 2012). "S&M vs. SPDY: Microsoft and Google battle over the future of HTTP 2.0". ExtremeTech. 
  15. ^ a b Grigorik, Ilya. "Life beyond HTTP 1.1: Google's SPDY". 
  16. ^ Willy Tarreau; Amos Jeffries; Adrien de Croy; Poul-Henning Kamp (March 29, 2012). "Proposal for a Network-Friendly HTTP Upgrade". Network Working Group. Internet Engineering Task Force. 
  17. ^ Doug Beaver (July 15, 2012). "HTTP2 Expression of Interest" (mailing list). W3C. 
  18. ^ Dio Synodinos (2012-11-30). "HTTP/2 First Draft Published". InfoQ. 
  19. ^ "SPDY: An experimental protocol for a faster web". The Chromium Projects. 
  20. ^ Chris Bentzel; Bence Béky (2015-02-09). "Hello HTTP/2, Goodbye SPDY". Chromium Blog. 
  21. ^ Belshe, M.; Peon, R.; Thomson, M. "Hypertext Transfer Protocol Version 2, Use of TLS Features". Retrieved 2015-02-10. 
  22. ^ a b "HTTP/2 Frequently Asked Questions". IETF HTTP Working Group. Retrieved 2014-09-08. 
  23. ^ "Networking/http2". MozillaWiki. Retrieved 2014-09-07. 
  24. ^ "mnot’s blog: HTTP/2 Implementation Status". 
  25. ^ a b c d Kamp, Poul-Henning (2015-01-06). "HTTP/2.0 – The IETF is Phoning It In (Bad protocol, bad politics)". ACM Queue. Retrieved 2015-01-12. 
  26. ^
  27. ^ Kamp, P. H. (2015). "Http/2.0". Communications of the ACM 58 (3): 40. doi:10.1145/2717515. 
  28. ^ Kamp, Poul-Henning (2015-01-07). "Re: Last Call: <draft-ietf-httpbis-http2-16.txt> (Hypertext Transfer Protocol version 2) to Proposed Standard". (Mailing list). Retrieved 2015-01-12. 
  29. ^ Lear, Eliot (2013-08-25). "Mandatory encryption *is* theater". (Mailing list). Retrieved 2015-01-26. 
  30. ^ Murenin, Constantine A. (2015-01-09). "Re: Last Call: <draft-ietf-httpbis-http2-16.txt> (Hypertext Transfer Protocol version 2) to Proposed Standard". (Mailing list). Retrieved 2015-01-12. 
  31. ^ Paul Hoffman. "draft-hoffman-httpbis-minimal-unauth-enc-01 - Minimal Unauthenticated Encryption (MUE) for HTTP-2". Internet Engineering Task Force. 
  32. ^ Mark Nottingham; Martin Thomson. "draft-nottingham-http2-encryption-03 - Opportunistic Encryption for HTTP URIs". Internet Engineering Task Force. 
  33. ^ Mark Nottingham; Martin Thomson. "draft-ietf-httpbis-http2-encryption-01 - Opportunistic Security for HTTP". Internet Engineering Task Force. 
  34. ^ a b Nottingham, Mark (June 7, 2014). "RFC2616 is Dead". Retrieved September 20, 2014. 
  35. ^ "HTTP/1.1, part 1: URIs, Connections, and Message Parsing - draft-ietf-httpbis-p1-messaging-00". December 20, 2007. Retrieved September 20, 2014. 
  36. ^ "Security Requirements for HTTP - draft-ietf-httpbis-security-properties-00.txt". January 23, 2008. Retrieved September 20, 2014. 
  37. ^ Nottingham, Mark (January 24, 2012). "Rechartering HTTPbis". Retrieved September 20, 2014. 
  38. ^ Nottingham, Mark (October 14, 2012). "Working Group Last Call for HTTP/1.1 p1 and p2". Retrieved September 20, 2014. 
  39. ^ Nottingham, Mark (October 23, 2012). "Second Working Group Last Call for HTTP/1.1 p4 to p7". Retrieved September 20, 2014. 
  40. ^ "SPDY Protocol - draft-ietf-httpbis-http2-00". HTTPbis Working Group. November 28, 2012. Retrieved September 20, 2014. 
  41. ^ Nottingham, Mark (November 30, 2012). "First draft of HTTP/2". Retrieved September 20, 2014. 
  42. ^ "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing". Archived from the original on 2014-08-13. Retrieved September 20, 2014. 
  43. ^ "Last Call: <draft-ietf-httpbis-p1-messaging-24.txt> (Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing) to Proposed Standard". The IESG. October 21, 2013. Retrieved September 20, 2014. 
  44. ^ The IESG (February 12, 2014). "Protocol Action: 'Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing' to Proposed Standard (draft-ietf-httpbis-p1-messaging-26.txt)". ietf-announce (Mailing list). Retrieved January 18, 2015. 
  45. ^ The RFC Editor Team (June 6, 2014). "RFC 7230 on Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing". ietf-announce (Mailing list). Retrieved January 18, 2015. 
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  48. ^ "IESG Agenda: 2015-01-22". IETF. Archived from the original on 2015-01-15. Retrieved January 15, 2015. 
  49. ^ The RFC Editor Team (May 14, 2015). "RFC 7540 on Hypertext Transfer Protocol Version 2 (HTTP/2)". ietf-announce (Mailing list). 
  50. ^ "http/2 module for apache httpd". Retrieved July 28, 2015. 
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  57. ^ "H2O". 
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  60. ^ "LSWS 5.0 Is Out – Support for HTTP/2, ESI, LiteMage Cache". April 17, 2015. 
  61. ^ Rob Trace; David Walp (October 8, 2014). "HTTP/2: The Long-Awaited Sequel". MSDN IEBlog. Microsoft Corporation. 
  62. ^ "nginx changelog". 2015-09-22. 
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  64. ^ "Radware Combines an Integrated HTTP/2 Gateway with its Leading Fastview Technology to Provide Web Server Platforms Increased Acceleration". July 20, 2015. 
  65. ^ stbuehler. "lighttpd Feature #2322 - Support for SPDY protocol". Lighttpd. 

External links[edit]