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draft-ietf-httpbis-rfc7838bis-00.txt draft-ietf-httpbis-rfc7838bis-latest.txt HTTP Working Group M. Bishop, Ed. HTTP Working Group M. Bishop, Ed. Internet-Draft Akamai Technologies Internet-Draft Akamai Technologies Intended status: Standards Track M. Thomson, Ed. Intended status: Standards Track M. Thomson, Ed. Expires: March 5, 2022 Mozilla Expires: November 22, 2025 Mozilla September 01, 2021 May 21, 2025 HTTP Alternative Services HTTP Alternative Services draft-ietf-httpbis-rfc7838bis-00 draft-ietf-httpbis-rfc7838bis-latest Abstract Abstract This document specifies "Alternative Services" for HTTP, which allow This document specifies "Alternative Services" for HTTP, which allow an origin's resources to be authoritatively available at a separate an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol network location, possibly accessed with a different protocol configuration. configuration. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at <https://datatracker.ietf.org/doc/draft-ietf-httpbis-rfc7838bis/>. Discussion of this document takes place on the HTTP Working Group mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at <https://lists.w3.org/Archives/Public/ietf-http-wg/>. Working Group information can be found at <https://httpwg.org/>. Source for this draft and an issue tracker can be found at <https://github.com/httpwg/http-extensions/labels/alt-svc>. Status of This Memo Status of This Memo This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." material or to cite them other than as "work in progress." This Internet-Draft will expire on March 5, 2022. This Internet-Draft will expire on November 22, 2025. Copyright Notice Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. described in the Simplified BSD License. Table of Contents Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Changes from RFC 7838 . . . . . . . . . . . . . . . . . . 3 1.1. Changes from RFC 7838 . . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 3 2. Alternative Services Concepts . . . . . . . . . . . . . . . . 4 2. Alternative Services Concepts . . . . . . . . . . . . . . . . 4 2.1. Host Authentication . . . . . . . . . . . . . . . . . . . 5 2.1. Host Authentication . . . . . . . . . . . . . . . . . . . 6 2.2. Alternative Service Caching . . . . . . . . . . . . . . . 6 2.2. Alternative Service Caching . . . . . . . . . . . . . . . 6 2.3. Requiring Server Name Indication . . . . . . . . . . . . 6 2.3. Requiring Server Name Indication . . . . . . . . . . . . 7 2.4. Using Alternative Services . . . . . . . . . . . . . . . 7 2.4. Using Alternative Services . . . . . . . . . . . . . . . 7 3. The Alt-Svc HTTP Header Field . . . . . . . . . . . . . . . . 8 3. The Alt-Svc HTTP Header Field . . . . . . . . . . . . . . . . 8 3.1. Caching Alt-Svc Header Field Values . . . . . . . . . . . 10 3.1. Caching Alt-Svc Header Field Values . . . . . . . . . . . 10 4. The ALTSVC HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 11 4. The ALTSVC Extension Frame . . . . . . . . . . . . . . . . . 11 5. The Alt-Used HTTP Header Field . . . . . . . . . . . . . . . 13 5. The Alt-Used HTTP Header Field . . . . . . . . . . . . . . . 13 6. The 421 (Misdirected Request) HTTP Status Code . . . . . . . 13 6. The 421 (Misdirected Request) HTTP Status Code . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 7.1. Header Field Registrations . . . . . . . . . . . . . . . 13 7.1. Header Field Registrations . . . . . . . . . . . . . . . 14 7.2. The ALTSVC HTTP/2 Frame Type . . . . . . . . . . . . . . 14 7.2. The ALTSVC HTTP/2 Frame Type . . . . . . . . . . . . . . 14 7.3. Alt-Svc Parameter Registry . . . . . . . . . . . . . . . 14 7.3. The ALTSVC HTTP/3 Frame Type . . . . . . . . . . . . . . 14 7.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 14 7.4. Alt-Svc Parameter Registry . . . . . . . . . . . . . . . 15 7.3.2. Registrations . . . . . . . . . . . . . . . . . . . . 15 7.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 15 7.4.2. Registrations . . . . . . . . . . . . . . . . . . . . 15 8. Internationalization Considerations . . . . . . . . . . . . . 15 8. Internationalization Considerations . . . . . . . . . . . . . 15 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9.1. Changing Ports . . . . . . . . . . . . . . . . . . . . . 15 9.1. Changing Ports . . . . . . . . . . . . . . . . . . . . . 15 9.2. Changing Hosts . . . . . . . . . . . . . . . . . . . . . 15 9.2. Changing Hosts . . . . . . . . . . . . . . . . . . . . . 16 9.3. Changing Protocols . . . . . . . . . . . . . . . . . . . 16 9.3. Changing Protocols . . . . . . . . . . . . . . . . . . . 17 9.4. Tracking Clients Using Alternative Services . . . . . . . 17 9.4. Tracking Clients Using Alternative Services . . . . . . . 17 9.5. Confusion regarding Request Scheme . . . . . . . . . . . 17 9.5. Confusion regarding Request Scheme . . . . . . . . . . . 17 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . 18 10.1. Normative References . . . . . . . . . . . . . . . . . . 18 10.2. Informative References . . . . . . . . . . . . . . . . . 19 10.2. Informative References . . . . . . . . . . . . . . . . . 19 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction 1. Introduction HTTP [RFC7230] conflates the identification of resources with their HTTP [HTTP] conflates the identification of resources with their location. In other words, "http://" and "https://" URIs are used to location. In other words, "http://" and "https://" URIs are used to both name and find things to interact with. both name and find things to interact with. In some cases, it is desirable to separate identification and In some cases, it is desirable to separate identification and location in HTTP; keeping the same identifier for a resource, but location in HTTP; keeping the same identifier for a resource, but interacting with it at a different location on the network. interacting with it at a different location on the network. For example: For example: o An origin server might wish to redirect a client to a different o An origin server might wish to redirect a client to a different server when it is under load, or it has found a server in a server when it is under load, or it has found a server in a location that is more local to the client. location that is more local to the client. o An origin server might wish to offer access to its resources using o An origin server might wish to offer access to its resources using a new protocol, such as HTTP/2 [RFC7540], or one using improved a new protocol, such as HTTP/3 [HTTP3], or one using improved security, such as Transport Layer Security (TLS) [RFC5246]. security, such as Transport Layer Security (TLS) [RFC8446]. o An origin server might wish to segment its clients into groups of o An origin server might wish to segment its clients into groups of capabilities, such as those supporting Server Name Indication capabilities, such as those supporting Server Name Indication (SNI) (Section 3 of [RFC6066]), for operational purposes. (SNI) (Section 3 of [RFC6066]), for operational purposes. This specification defines a new concept in HTTP, "Alternative This specification defines a new concept in HTTP, "Alternative Services", that allows an origin server to nominate additional means Services", that allows an origin server to nominate additional means of interacting with it on the network. It defines a general of interacting with it on the network. It defines a general framework for this in Section 2, along with specific mechanisms for framework for this in Section 2, along with specific mechanisms for advertising their existence using HTTP header fields (Section 3) or advertising their existence using HTTP header fields (Section 3) or HTTP/2 frames (Section 4), plus a way to indicate that an alternative HTTP/2 frames (Section 4), plus a way to indicate that an alternative service was used (Section 5). service was used (Section 5). It also endorses the status code 421 (Misdirected Request) It also endorses the status code 421 (Misdirected Request) (Section 6) that origin servers or their nominated alternatives can (Section 6) that origin servers or their nominated alternatives can use to indicate that they are not authoritative for a given origin, use to indicate that they are not authoritative for a given origin, in cases where the wrong location is used. in cases where the wrong location is used. 1.1. Changes from RFC 7838 1.1. Changes from RFC 7838 No substantive changes. o Added an ALTSVC frame for HTTP/3. 1.2. Notational Conventions 1.2. Notational Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119]. This document uses the Augmented BNF defined in [RFC5234] and updated This document uses the Augmented BNF defined in [RFC5234] and updated by [RFC7405] along with the "#rule" extension defined in Section 7 of by [RFC7405] along with the "#rule" extension defined in [RFC7230]. The rules below are defined in [RFC5234], [RFC7230], and Section 5.6.1 of [HTTP]. The rules below are defined in [RFC5234], [RFC7234]: [HTTP], and [Caching]: OWS = <OWS, see [RFC7230], Section 3.2.3> OWS = <OWS, see [HTTP], Section 5.6.3> delta-seconds = <delta-seconds; see [RFC7234], Section 1.2.1> delta-seconds = <delta-seconds; see [Caching], Section 1.2.2> port = <port, see [RFC7230], Section 2.7> port = <port, see [HTTP], Section 4.1> quoted-string = <quoted-string, see [RFC7230], Section 3.2.6> quoted-string = <quoted-string, see [HTTP], Section 5.6.4> token = <token, see [RFC7230], Section 3.2.6> token = <token, see [HTTP], Section 5.6.2> uri-host = <uri-host, see [RFC7230], Section 2.7> uri-host = <uri-host, see [HTTP], Section 4.1> 2. Alternative Services Concepts 2. Alternative Services Concepts This specification defines a new concept in HTTP, the "Alternative This specification defines a new concept in HTTP, the "Alternative Service". When an origin [RFC6454] has resources that are accessible Service". When an origin [RFC6454] has resources that are accessible through a different protocol/host/port combination, it is said to through a different protocol/host/port combination, it is said to have an alternative service available. have an alternative service available. An alternative service can be used to interact with the resources on An alternative service can be used to interact with the resources on an origin server at a separate location on the network, possibly an origin server at a separate location on the network, possibly using a different protocol configuration. Alternative services are using a different protocol configuration. Alternative services are considered authoritative for an origin's resources, in the sense of considered authoritative for an origin's resources, in the sense of Section 9.1 of [RFC7230]. Section 4.3 of [HTTP]. For example, an origin: For example, an origin: ("http", "www.example.com", "80") ("http", "www.example.com", "80") might declare that its resources are also accessible at the might declare that its resources are also accessible at the alternative service: alternative service: ("h2", "new.example.com", "81") ("h2", "new.example.com", "81") skipping to change at page 5, line 6 ¶ skipping to change at page 5, line 19 ¶ options for that protocol as well. options for that protocol as well. This means that clients using an alternative service can change the This means that clients using an alternative service can change the host, port, and protocol that they are using to fetch resources, but host, port, and protocol that they are using to fetch resources, but these changes MUST NOT be propagated to the application that is using these changes MUST NOT be propagated to the application that is using HTTP; from that standpoint, the URI being accessed and all HTTP; from that standpoint, the URI being accessed and all information derived from it (scheme, host, and port) are the same as information derived from it (scheme, host, and port) are the same as before. before. Importantly, this includes its security context; in particular, when Importantly, this includes its security context; in particular, when TLS [RFC5246] is used to authenticate, the alternative service will TLS [RFC8446] is used to authenticate, the alternative service will need to present a certificate for the origin's host name, not that of need to present a certificate for the origin's host name, not that of the alternative. Likewise, the Host header field ([RFC7230], the alternative. Likewise, the Host header field (Section 7.2 of Section 5.4) is still derived from the origin, not the alternative [HTTP]) is still derived from the origin, not the alternative service service (just as it would if a CNAME were being used). (just as it would if a CNAME were being used). The changes MAY, however, be made visible in debugging tools, The changes MAY, however, be made visible in debugging tools, consoles, etc. consoles, etc. Formally, an alternative service is identified by the combination of: Formally, an alternative service is identified by the combination of: o An Application Layer Protocol Negotiation (ALPN) protocol name, as o An Application-Layer Protocol Negotiation (ALPN) protocol name, as per [RFC7301] per [RFC7301] o A host, as per Section 3.2.2 of [RFC3986] o A host, as per Section 3.2.2 of [RFC3986] o A port, as per Section 3.2.3 of [RFC3986] o A port, as per Section 3.2.3 of [RFC3986] The ALPN protocol name is used to identify the application protocol The ALPN protocol name is used to identify the application protocol or suite of protocols used by the alternative service. Note that for or suite of protocols used by the alternative service. Note that for the purpose of this specification, an ALPN protocol name implicitly the purpose of this specification, an ALPN protocol name implicitly includes TLS in the suite of protocols it identifies, unless includes TLS in the suite of protocols it identifies, unless specified otherwise in its definition. In particular, the ALPN name specified otherwise in its definition. In particular, the ALPN name "http/1.1", registered by Section 6 of [RFC7301], identifies HTTP/1.1 "http/1.1", registered by Section 6 of [RFC7301], identifies HTTP/1.1 over TLS. over TLS. Additionally, each alternative service MUST have a freshness Additionally, each alternative service MUST have a freshness lifetime, expressed in seconds (see Section 2.2). lifetime, expressed in seconds (see Section 2.2). There are many ways that a client could discover the alternative There are many ways that a client could discover the alternative service(s) associated with an origin. This document describes two service(s) associated with an origin. This document describes two such mechanisms: the "Alt-Svc" HTTP header field (Section 3) and the such mechanisms: the "Alt-Svc" HTTP header field (Section 3) and the "ALTSVC" HTTP/2 frame type (Section 4). "ALTSVC" frame type for HTTP/2 and HTTP/3 (Section 4). The remainder of this section describes requirements that are common The remainder of this section describes requirements that are common to alternative services, regardless of how they are discovered. to alternative services, regardless of how they are discovered. 2.1. Host Authentication 2.1. Host Authentication Clients MUST have reasonable assurances that the alternative service Clients MUST have reasonable assurances that the alternative service is under control of and valid for the whole origin. This mitigates is under control of and valid for the whole origin. This mitigates the attack described in Section 9.2. the attack described in Section 9.2. skipping to change at page 8, line 28 ¶ skipping to change at page 8, line 40 ¶ The field value consists either of a list of values, each of which The field value consists either of a list of values, each of which indicates one alternative service, or the keyword "clear". indicates one alternative service, or the keyword "clear". A field value containing the special value "clear" indicates that the A field value containing the special value "clear" indicates that the origin requests all alternatives for that origin to be invalidated origin requests all alternatives for that origin to be invalidated (including those specified in the same response, in case of an (including those specified in the same response, in case of an invalid reply containing both "clear" and alternative services). invalid reply containing both "clear" and alternative services). ALPN protocol names are octet sequences with no additional ALPN protocol names are octet sequences with no additional constraints on format. Octets not allowed in tokens ([RFC7230], constraints on format. Octets not allowed in tokens (Section 5.6.2 Section 3.2.6) MUST be percent-encoded as per Section 2.1 of of [HTTP]) MUST be percent-encoded as per Section 2.1 of [RFC3986]. [RFC3986]. Consequently, the octet representing the percent Consequently, the octet representing the percent character "%" (hex character "%" (hex 25) MUST be percent-encoded as well. 25) MUST be percent-encoded as well. In order to have precisely one way to represent any ALPN protocol In order to have precisely one way to represent any ALPN protocol name, the following additional constraints apply: name, the following additional constraints apply: 1. Octets in the ALPN protocol name MUST NOT be percent-encoded if 1. Octets in the ALPN protocol name MUST NOT be percent-encoded if they are valid token characters except "%", and they are valid token characters except "%", and 2. When using percent-encoding, uppercase hex digits MUST be used. 2. When using percent-encoding, uppercase hex digits MUST be used. With these constraints, recipients can apply simple string comparison With these constraints, recipients can apply simple string comparison to match protocol identifiers. to match protocol identifiers. The "alt-authority" component consists of an OPTIONAL uri-host The "alt-authority" component consists of an OPTIONAL uri-host ("host" in Section 3.2.2 of [RFC3986]), a colon (":"), and a port ("host" in Section 3.2.2 of [RFC3986]), a colon (":"), and a port number. number. For example: For example: Alt-Svc: h2=":8000" Alt-Svc: h2=":8000" This indicates the "h2" protocol ([RFC7540]) on the same host using the indicated port 8000. This indicates the "h2" protocol ([HTTP2]) on the same host using the indicated port 8000. An example involving a change of host: An example involving a change of host: Alt-Svc: h2="new.example.org:80" Alt-Svc: h2="new.example.org:80" This indicates the "h2" protocol on the host "new.example.org", This indicates the "h2" protocol on the host "new.example.org", running on port 80. Note that the "quoted-string" syntax needs to be running on port 80. Note that the "quoted-string" syntax needs to be used because ":" is not an allowed character in "token". used because ":" is not an allowed character in "token". Examples for protocol name escaping: Examples for protocol name escaping: skipping to change at page 9, line 29 ¶ skipping to change at page 9, line 41 ¶ +--------------------+-------------+---------------------+ +--------------------+-------------+---------------------+ | h2 | h2 | No escaping needed | | h2 | h2 | No escaping needed | | | | | | | | | | w=x:y#z | w%3Dx%3Ay#z | "=" and ":" escaped | | w=x:y#z | w%3Dx%3Ay#z | "=" and ":" escaped | | | | | | | | | | x%y | x%25y | "%" needs escaping | | x%y | x%25y | "%" needs escaping | +--------------------+-------------+---------------------+ +--------------------+-------------+---------------------+ Alt-Svc MAY occur in any HTTP response message, regardless of the Alt-Svc MAY occur in any HTTP response message, regardless of the status code. Note that recipients of Alt-Svc can ignore the header status code. Note that recipients of Alt-Svc can ignore the header field (and are required to in some situations; see Sections 2.1 and field (and are required to in some situations; see Section 2.1 and 6). Section 6). The Alt-Svc field value can have multiple values: The Alt-Svc field value can have multiple values: Alt-Svc: h2="alt.example.com:8000", h2=":443" Alt-Svc: h2="alt.example.com:8000", h2=":443" When multiple values are present, the order of the values reflects When multiple values are present, the order of the values reflects the server's preference (with the first value being the most the server's preference (with the first value being the most preferred alternative). preferred alternative). The value(s) advertised by Alt-Svc can be used by clients to open a The value(s) advertised by Alt-Svc can be used by clients to open a new connection to an alternative service. Subsequent requests can new connection to an alternative service. Subsequent requests can start using this new connection immediately or can continue using the start using this new connection immediately or can continue using the existing connection while the new connection is created. existing connection while the new connection is created. When using HTTP/2 ([RFC7540]), servers SHOULD instead send an ALTSVC When using HTTP/2 ([HTTP2]), servers SHOULD instead send an ALTSVC frame (Section 4). A single ALTSVC frame can be sent for a frame (Section 4). A single ALTSVC frame can be sent for a connection; a new frame is not needed for every request. Note that, connection; a new frame is not needed for every request. Note that, despite this recommendation, Alt-Svc header fields remain valid in despite this recommendation, Alt-Svc header fields remain valid in responses delivered over HTTP/2. responses delivered over HTTP/2. Each "alt-value" is followed by an OPTIONAL semicolon-separated list Each "alt-value" is followed by an OPTIONAL semicolon-separated list of additional parameters, each such "parameter" comprising a name and of additional parameters, each such "parameter" comprising a name and a value. a value. This specification defines two parameters: "ma" and "persist", This specification defines two parameters: "ma" and "persist", defined in Section 3.1. Unknown parameters MUST be ignored. That defined in Section 3.1. Unknown parameters MUST be ignored. That is, the values (alt-value) they appear in MUST be processed as if the is, the values (alt-value) they appear in MUST be processed as if the unknown parameter was not present. unknown parameter was not present. New parameters can be defined in extension specifications (see New parameters can be defined in extension specifications (see Section 7.3 for registration details). Section 7.4 for registration details). Note that all field elements that allow "quoted-string" syntax MUST Note that all field elements that allow "quoted-string" syntax MUST be processed as per Section 3.2.6 of [RFC7230]. be processed as per Section 5.6.4 of [HTTP]. 3.1. Caching Alt-Svc Header Field Values 3.1. Caching Alt-Svc Header Field Values When an alternative service is advertised using Alt-Svc, it is When an alternative service is advertised using Alt-Svc, it is considered fresh for 24 hours from generation of the message. This considered fresh for 24 hours from generation of the message. This can be modified with the "ma" (max-age) parameter. can be modified with the "ma" (max-age) parameter. Syntax: Syntax: ma = delta-seconds; see [RFC7234], Section 1.2.1 ma = delta-seconds; see [Caching], Section 1.2.2 The delta-seconds value indicates the number of seconds since the The delta-seconds value indicates the number of seconds since the response was generated for which the alternative service is response was generated for which the alternative service is considered fresh. considered fresh. Alt-Svc: h2=":443"; ma=3600 Alt-Svc: h2=":443"; ma=3600 See Section 4.2.3 of [RFC7234] for details on determining the See Section 4.2.3 of [Caching] for details on determining the response age. response age. For example, a response: For example, a response: HTTP/1.1 200 OK HTTP/1.1 200 OK Content-Type: text/html Content-Type: text/html Cache-Control: max-age=600 Cache-Control: max-age=600 Age: 30 Age: 30 Alt-Svc: h2=":8000"; ma=60 Alt-Svc: h2=":8000"; ma=60 skipping to change at page 11, line 33 ¶ skipping to change at page 11, line 45 ¶ For example: For example: Alt-Svc: h2=":443"; ma=2592000; persist=1 Alt-Svc: h2=":443"; ma=2592000; persist=1 This specification only defines a single value for "persist". This specification only defines a single value for "persist". Clients MUST ignore "persist" parameters with values other than "1". Clients MUST ignore "persist" parameters with values other than "1". See Section 2.2 for general requirements on caching alternative See Section 2.2 for general requirements on caching alternative services. services. 4. The ALTSVC HTTP/2 Frame 4. The ALTSVC Extension Frame The ALTSVC HTTP/2 frame (Section 4 of [RFC7540]) advertises the The ALTSVC frame advertises the availability of an alternative availability of an alternative service to an HTTP/2 client. service to an HTTP/2 or HTTP/3 client. The ALTSVC frame is a non-critical extension to HTTP/2. Endpoints The ALTSVC frame is a separate non-critical extension in each that do not support this frame will ignore it (as per the protocol. Endpoints that do not support this frame will ignore it extensibility rules defined in Section 4.1 of [RFC7540]). (as per the extensibility rules defined in Section 4.1 of [HTTP2] and Section 4.1 of [HTTP3]). An ALTSVC frame from a server to a client on a stream other than An ALTSVC frame from a server to a client on a request stream or a stream 0 indicates that the conveyed alternative service is push stream indicates that the conveyed alternative service is associated with the origin of that stream. associated with the origin of that stream. An ALTSVC frame from a server to a client on stream 0 indicates that An ALTSVC frame from a server to a client on the control stream (stream 0 in HTTP/2 or a stream of type 0 in HTTP/3) indicates that the conveyed alternative service is associated with the origin the conveyed alternative service is associated with the origin contained in the Origin field of the frame. An association with an contained in the Origin field of the frame. An association with an origin that the client does not consider authoritative for the origin that the client does not consider authoritative for the current connection MUST be ignored. current connection MUST be ignored. The ALTSVC frame type is 0xa (decimal 10). The ALTSVC frame type is 0xa (decimal 10) in both protocols. +-------------------------------+-------------------------------+ +-------------------------------+-------------------------------+ | Origin-Len (16) | Origin? (*) ... | Origin-Len (16) | Origin? (*) ... +-------------------------------+-------------------------------+ +-------------------------------+-------------------------------+ | Alt-Svc-Field-Value (*) ... | Alt-Svc-Field-Value (*) ... +---------------------------------------------------------------+ +---------------------------------------------------------------+ ALTSVC Frame Payload ALTSVC Frame Payload The ALTSVC frame contains the following fields: The ALTSVC frame contains the following fields: skipping to change at page 12, line 27 ¶ skipping to change at page 12, line 42 ¶ Origin: An OPTIONAL sequence of characters containing the ASCII Origin: An OPTIONAL sequence of characters containing the ASCII serialization of an origin (Section 6.2 of [RFC6454]) to which the serialization of an origin (Section 6.2 of [RFC6454]) to which the alternative service is applicable. alternative service is applicable. Alt-Svc-Field-Value: A sequence of octets (length determined by Alt-Svc-Field-Value: A sequence of octets (length determined by subtracting the length of all preceding fields from the frame subtracting the length of all preceding fields from the frame length) containing a value identical to the Alt-Svc field value length) containing a value identical to the Alt-Svc field value defined in Section 3 (ABNF production "Alt-Svc"). defined in Section 3 (ABNF production "Alt-Svc"). The ALTSVC frame does not define any flags. The ALTSVC frame does not define any flags in HTTP/2; there is no generic flag field for HTTP/3 frames. The ALTSVC frame is intended for receipt by clients. A device acting The ALTSVC frame is intended for receipt by clients. A device acting as a server MUST ignore it. as a server MUST ignore it. An ALTSVC frame on stream 0 with empty (length 0) "Origin" An ALTSVC frame on the control stream with empty (length 0) "Origin" information is invalid and MUST be ignored. An ALTSVC frame on a information is invalid and MUST be ignored. An ALTSVC frame on a stream other than stream 0 containing non-empty "Origin" information request or push stream containing non-empty "Origin" information is is invalid and MUST be ignored. invalid and MUST be ignored. The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT forward ALTSVC frames, though it can use the information contained in forward ALTSVC frames, though it can use the information contained in ALTSVC frames in forming new ALTSVC frames to send to its own ALTSVC frames in forming new ALTSVC frames to send to its own clients. clients. Receiving an ALTSVC frame is semantically equivalent to receiving an Receiving an ALTSVC frame is semantically equivalent to receiving an Alt-Svc header field. As a result, the ALTSVC frame causes Alt-Svc header field. As a result, the ALTSVC frame causes alternative services for the corresponding origin to be replaced. alternative services for the corresponding origin to be replaced. Note that it would be unwise to mix the use of Alt-Svc header fields Note that it would be unwise to mix the use of Alt-Svc header fields with the use of ALTSVC frames, as the sequence of receipt might be with the use of ALTSVC frames, as the sequence of receipt might be hard to predict. hard to predict. 5. The Alt-Used HTTP Header Field 5. The Alt-Used HTTP Header Field The Alt-Used header field is used in requests to identify the The Alt-Used header field is used in requests to identify the alternative service in use, just as the Host header field alternative service in use, just as the Host header field (Section 5.4 of [RFC7230]) identifies the host and port of the (Section 7.2 of [HTTP]) identifies the host and port of the origin. origin. Alt-Used = uri-host [ ":" port ] Alt-Used = uri-host [ ":" port ] Alt-Used is intended to allow alternative services to detect loops, Alt-Used is intended to allow alternative services to detect loops, differentiate traffic for purposes of load balancing, and generally differentiate traffic for purposes of load balancing, and generally to ensure that it is possible to identify the intended destination of to ensure that it is possible to identify the intended destination of traffic, since introducing this information after a protocol is in traffic, since introducing this information after a protocol is in use has proven to be problematic. use has proven to be problematic. When using an alternative service, clients SHOULD include an Alt-Used When using an alternative service, clients SHOULD include an Alt-Used header field in all requests. header field in all requests. For example: For example: GET /thing HTTP/1.1 GET /thing HTTP/1.1 Host: origin.example.com Host: origin.example.com Alt-Used: alternate.example.net Alt-Used: alternate.example.net 6. The 421 (Misdirected Request) HTTP Status Code 6. The 421 (Misdirected Request) HTTP Status Code The 421 (Misdirected Request) status code is defined in Section 9.1.2 The 421 (Misdirected Request) status code is defined in of [RFC7540] to indicate that the current server instance is not Section 15.5.20 of [HTTP] to indicate that the current server authoritative for the requested resource. This can be used to instance is not authoritative for the requested resource. This can indicate that an alternative service is not authoritative; see be used to indicate that an alternative service is not authoritative; Section 2). see Section 2). Clients receiving 421 (Misdirected Request) from an alternative Clients receiving 421 (Misdirected Request) from an alternative service MUST remove the corresponding entry from its alternative service MUST remove the corresponding entry from its alternative service cache (see Section 2.2) for that origin. Regardless of the service cache (see Section 2.2) for that origin. Regardless of the idempotency of the request method, they MAY retry the request, either idempotency of the request method, they MAY retry the request, either at another alternative server, or at the origin. at another alternative server, or at the origin. An Alt-Svc header field in a 421 (Misdirected Request) response MUST An Alt-Svc header field in a 421 (Misdirected Request) response MUST be ignored. be ignored. skipping to change at page 14, line 9 ¶ skipping to change at page 14, line 20 ¶ 7.1. Header Field Registrations 7.1. Header Field Registrations HTTP header fields are registered within the "Message Headers" HTTP header fields are registered within the "Message Headers" registry maintained at <https://www.iana.org/assignments/message- registry maintained at <https://www.iana.org/assignments/message- headers/>. headers/>. This document defines the following HTTP header fields, so their This document defines the following HTTP header fields, so their associated registry entries have been added according to the associated registry entries have been added according to the permanent registrations below (see [BCP90]): permanent registrations below (see [BCP90]): +-------------------+----------+----------+-----------+ +-------------------+----------+----------+------------+ | Header Field Name | Protocol | Status | Reference | | Header Field Name | Protocol | Status | Reference | +-------------------+----------+----------+-----------+ +-------------------+----------+----------+------------+ | Alt-Svc | http | standard | Section 3 | | Alt-Svc | http | standard | Section 3 | | | | | | | | | | | | Alt-Used | http | standard | Section 5 | | Alt-Used | http | standard | Section 5 | +-------------------+----------+----------+-----------+ +-------------------+----------+----------+------------+ The change controller is: "IETF (iesg@ietf.org) -- Internet The change controller is: "IETF (iesg@ietf.org) -- Internet Engineering Task Force". Engineering Task Force". 7.2. The ALTSVC HTTP/2 Frame Type 7.2. The ALTSVC HTTP/2 Frame Type This document registers the ALTSVC frame type in the "HTTP/2 Frame This document registers the ALTSVC frame type in the "HTTP/2 Frame Type" registry (Section 11.2 of [RFC7540]). Type" registry (Section 11.2 of [HTTP2]). Frame Type: ALTSVC Frame Type: ALTSVC Code: 0xa Code: 0xa Specification: Section 4 of this document Specification: Section 4 of this document 7.3. Alt-Svc Parameter Registry 7.3. The ALTSVC HTTP/3 Frame Type This document registers the ALTSVC frame type in the "HTTP/3 Frame Type" registry (Section 11.2.1 of [HTTP3]). Frame Type: ALTSVC Value: 0xa Specification: Section 4 of this document 7.4. Alt-Svc Parameter Registry The "Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter Registry" The "Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter Registry" defines the name space for parameters. It has been created and will defines the name space for parameters. It has been created and will be maintained at <http://www.iana.org/assignments/http-alt-svc- be maintained at <http://www.iana.org/assignments/http-alt-svc- parameters>. parameters>. 7.3.1. Procedure 7.4.1. Procedure A registration MUST include the following fields: A registration MUST include the following fields: o Parameter Name o Parameter Name o Pointer to specification text o Pointer to specification text Values to be added to this name space require Expert Review (see Values to be added to this name space require Expert Review (see Section 4.1 of [RFC5226]). Section 4.1 of [RFC5226]). 7.3.2. Registrations 7.4.2. Registrations The "Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter Registry" The "Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter Registry" has been populated with the registrations below: has been populated with the registrations below: +-------------------+-------------+ +-------------------+--------------+ | Alt-Svc Parameter | Reference | | Alt-Svc Parameter | Reference | +-------------------+-------------+ +-------------------+--------------+ | ma | Section 3.1 | | ma | Section 3.1 | | | | | | | | persist | Section 3.1 | | persist | Section 3.1 | +-------------------+-------------+ +-------------------+--------------+ 8. Internationalization Considerations 8. Internationalization Considerations An internationalized domain name that appears in either the header An internationalized domain name that appears in either the header field (Section 3) or the HTTP/2 frame (Section 4) MUST be expressed field (Section 3) or the HTTP/2 frame (Section 4) MUST be expressed using A-labels (Section 2.3.2.1 of [RFC5890]). using A-labels (Section 2.3.2.1 of [RFC5890]). 9. Security Considerations 9. Security Considerations 9.1. Changing Ports 9.1. Changing Ports skipping to change at page 17, line 44 ¶ skipping to change at page 18, line 11 ¶ connection to be migrated to a different protocol and port, these connection to be migrated to a different protocol and port, these applications can become confused about the security properties of a applications can become confused about the security properties of a given connection, sending information (for example, cookies and given connection, sending information (for example, cookies and content) that is intended for a secure context (such as an "https://" content) that is intended for a secure context (such as an "https://" URI) to a client that is not treating it as one. URI) to a client that is not treating it as one. This risk can be mitigated in servers by using the URI scheme This risk can be mitigated in servers by using the URI scheme explicitly carried by the protocol (such as ":scheme" in HTTP/2 or explicitly carried by the protocol (such as ":scheme" in HTTP/2 or the "absolute form" of the request target in HTTP/1.1) as an the "absolute form" of the request target in HTTP/1.1) as an indication of security context, instead of other connection indication of security context, instead of other connection properties (Section 8.1.2.3 of [RFC7540] and Section 5.3.2 of properties (Section 8.3.1 of [HTTP2] and Section 3.2.2 of [HTTP11]). [RFC7230]). When the protocol does not explicitly carry the scheme (as is usually When the protocol does not explicitly carry the scheme (as is usually the case for HTTP/1.1 over TLS), servers can mitigate this risk by the case for HTTP/1.1 over TLS), servers can mitigate this risk by either assuming that all requests have an insecure context, or by either assuming that all requests have an insecure context, or by refraining from advertising alternative services for insecure schemes refraining from advertising alternative services for insecure schemes (for example, HTTP). (for example, HTTP). 10. References 10. References 10.1. Normative References 10.1. Normative References [Caching] Fielding, R., Nottingham, M., and J. Reschke, "HTTP Caching", draft-ietf-httpbis-cache-19 (work in progress), September 2021. [HTTP] Fielding, R., Nottingham, M., and J. Reschke, "HTTP Semantics", draft-ietf-httpbis-semantics-19 (work in progress), September 2021. [HTTP11] Fielding, R., Nottingham, M., and J. Reschke, "HTTP/1.1", draft-ietf-httpbis-messaging-19 (work in progress), September 2021. [HTTP2] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer Protocol Version 2 (HTTP/2)", draft-ietf-httpbis-http2-17 (work in progress), February 2015. [HTTP3] Bishop, M., "HTTP/3", draft-ietf-quic-http-34 (work in progress), February 2021. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000, <https://www.rfc-editor.org/info/rfc2818>. <https://www.rfc-editor.org/info/rfc2818>. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform skipping to change at page 18, line 47 ¶ skipping to change at page 19, line 34 ¶ [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, DOI 10.17487/RFC6066, January 2011, <https://www.rfc-editor.org/info/rfc6066>. <https://www.rfc-editor.org/info/rfc6066>. [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, DOI 10.17487/RFC6454, December 2011, DOI 10.17487/RFC6454, December 2011, <https://www.rfc-editor.org/info/rfc6454>. <https://www.rfc-editor.org/info/rfc6454>. [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, <https://www.rfc-editor.org/info/rfc7230>. [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, DOI 10.17487/RFC7234, June 2014, <https://www.rfc-editor.org/info/rfc7234>. [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, July 2014, <https://www.rfc-editor.org/info/rfc7301>. July 2014, <https://www.rfc-editor.org/info/rfc7301>. [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC 7405, DOI 10.17487/RFC7405, December 2014, RFC 7405, DOI 10.17487/RFC7405, December 2014, <https://www.rfc-editor.org/info/rfc7405>. <https://www.rfc-editor.org/info/rfc7405>. [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, <https://www.rfc-editor.org/info/rfc7540>. 10.2. Informative References 10.2. Informative References [BCP90] Consisting of: [RFC3864], [BCP90] Consisting of: [RFC3864], <https://www.rfc-editor.org/info/bcp90>. <https://www.rfc-editor.org/info/bcp90>. [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864, DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004, <https://www.rfc-editor.org/info/rfc3864>. <https://www.rfc-editor.org/info/rfc3864>. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <https://www.rfc-editor.org/info/rfc5246>. [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011, <https://www.rfc-editor.org/info/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>. [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April 2015, <https://www.rfc-editor.org/info/rfc7469>. 2015, <https://www.rfc-editor.org/info/rfc7469>. [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP Alternative Services", RFC 7838, DOI 10.17487/RFC7838, Alternative Services", RFC 7838, DOI 10.17487/RFC7838, April 2016, <https://www.rfc-editor.org/info/rfc7838>. April 2016, <https://www.rfc-editor.org/info/rfc7838>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. Acknowledgments Acknowledgments The previous version of this document was authored by Mark The previous version of this document was authored by Mark Nottingham, Patrick McManus, and Julian F. Reschke. [RFC7838] Nottingham, Patrick McManus, and Julian F. Reschke. [RFC7838] contains a more extensive list of people who contributed to that contains a more extensive list of people who contributed to that document. document. Authors' Addresses Authors' Addresses Mike Bishop (editor) Mike Bishop (editor) End of changes. 53 change blocks. 110 lines changed or deleted 142 lines changed or added
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