draft-ietf-httpbis-alt-svc.xml

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<!DOCTYPE rfc [
  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
  <!ENTITY mdash "&#8212;">
]>

<rfc ipr="trust200902" 
     category="std"
     docName="draft-ietf-httpbis-alt-svc-latest"
     x:maturity-level="proposed"
     xmlns:x="http://purl.org/net/xml2rfc/ext">
  <x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
  <front>
    <title abbrev="Alternative Services">HTTP Alternative Services</title>

    <author initials="M." surname="Nottingham" fullname="Mark Nottingham">
      <organization>Akamai</organization>
      <address>
        <email>mnot@mnot.net</email>
        <uri>http://www.mnot.net/</uri>
      </address>
    </author>

    <author initials="P." surname="McManus" fullname="Patrick McManus">
      <organization>Mozilla</organization>
      <address>
        <email>mcmanus@ducksong.com</email>
        <uri>https://mozillians.org/u/pmcmanus/</uri>
      </address>
    </author>

    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address>
        <email>julian.reschke@greenbytes.de</email>
        <uri>http://greenbytes.de/tech/webdav/</uri>
      </address>
    </author>

    <date year="2014"/>
    <area>Applications</area>
    <workgroup>HTTPbis</workgroup>
    <keyword>HTTP</keyword>

    <abstract>
      <t>
        This document specifies "alternative services" for HTTP, which allow an
        origin's resources to be authoritatively available at a separate network
        location, possibly accessed with a different protocol configuration.</t>
    </abstract>

    <note title="Editorial Note (To be removed by RFC Editor)">
      <t>
        Discussion of this draft takes place on the HTTPBIS working group mailing list
        (ietf-http-wg@w3.org), which is archived at <eref
        target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
      </t>
      <t>
        Working Group information can be found at <eref
        target="http://tools.ietf.org/wg/httpbis/"/>; that specific to HTTP/2 are at <eref
        target="http://http2.github.io/"/>.
      </t>
      <t>
        The changes in this draft are summarized in <xref
        target="change.log"/>.
      </t>
    </note>

  </front>
  <middle>

<section anchor="introduction" title="Introduction">
<t>
   HTTP <xref target="HTTP-p1"/> conflates the identification of
   resources with their location. In other words, "http://" (and "https://") URLs are
   used to both name and find things to interact with.
</t>
<t>
   In some cases, it is desirable to separate these aspects; to be able to keep
   the same identifier for a resource, but interact with it using a different
   location on the network.
</t>
<t>For example:
  <list style="symbols">
    <t>
       An origin server might wish to redirect a client to an alternative when it
       needs to go down for maintenance, or it has found an alternative in a
       location that is more local to the client.
    </t>
    <t>
       An origin server might wish to offer access to its resources using a new
       protocol (such as HTTP/2, see <xref target="HTTP2"/>) or one using improved
       security (such as Transport Layer Security (TLS), see <xref target="RFC5246"/>).
    </t>
    <t>
       An origin server might wish to segment its clients into groups of
       capabilities, such as those supporting Server Name Indication (SNI,
       see <xref target="RFC6066" x:sec="3" x:fmt="of"/>) and those not
       supporting it, for operational purposes.
    </t>
  </list>
</t>
<t>
   This specification defines a new concept in HTTP, "Alternative Services", that
   allows a resource to nominate additional means of interacting with it on the
   network. It defines a general framework for this in <xref target="alternative"/>, along with
   a specific mechanism for discovering them using HTTP header fields in <xref target="alt-svc"/>.
</t>
<t>
   It also introduces a new status code in <xref target="status"/>, so that origin servers (or
   their nominated alternatives) can indicate that they are not authoritative for
   a given origin, in cases where the wrong location is used.
</t>

<section title="Notational Conventions" anchor="notational-conventions">
<t>
  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
  "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
  interpreted as described in <xref target="RFC2119"/>.
</t>
<t>
  This document uses the Augmented BNF defined in <xref target="RFC5234"/>
  along with the "OWS", "delta-seconds", "parameter", "port", "token",
  and "uri-host" rules from <xref target="HTTP-p1"/>, and uses the "#rule"
  extension defined in <xref target="HTTP-p1" x:rel="#abnf.extension" x:fmt="sec"/> of that document.
</t>
</section>

    </section>

<section title="Alternative Services Concepts" anchor="alternative">
<t>
   This specification defines a new concept in HTTP, the "<x:dfn>alternative service</x:dfn>".
   When an origin (see <xref target="RFC6454"/>) has resources that are accessible through a
   different protocol / host / port combination, it is said to have an alternative
   service.
</t>
<t>
   An alternative service can be used to interact with the resources on an origin
   server at a separate location on the network, possibly using a different
   protocol configuration. Alternative services are considered authoritative for
   an origin's resources, in the sense of <xref target="HTTP-p1" x:rel="#establishing.authority" x:fmt=","/>.
</t>
<figure>
  <preamble>For example, an origin:</preamble>
  <artwork type="example">
("http", "www.example.com", "80")
</artwork>
</figure>
<figure>
<preamble>might declare that its resources are also accessible at the alternative service:</preamble>
<artwork type="example">
("h2", "new.example.com", "81")
</artwork>
</figure>
<t>
   By their nature, alternative services are explicitly at the granularity of an
   origin; i.e., they cannot be selectively applied to resources within an origin.
</t>
<t>
   Alternative services do not replace or change the origin for any given resource;
   in general, they are not visible to the software "above" the access mechanism.
   The alternative service is essentially alternative routing information that can
   also be used to reach the origin in the same way that DNS CNAME or SRV records
   define routing information at the name resolution level. Each origin maps to a
   set of these routes &mdash; the default route is derived from origin itself and the
   other routes are introduced based on alternative-protocol information.
</t>
<t>
   Furthermore, it is important to note that the first member of an alternative
   service tuple is different from the "scheme" component of an origin; it is more
   specific, identifying not only the major version of the protocol being used,
   but potentially communication options for that protocol.
</t>
<t>
   This means that clients using an alternative service will change the host, port
   and protocol that they are using to fetch resources, but these changes &MUST-NOT;
   be propagated to the application that is using HTTP; from that standpoint, the
   URI being accessed and all information derived from it (scheme, host, port) are
   the same as before.
</t>
<t>
   Importantly, this includes its security context; in particular, when TLS
   <xref target="RFC5246"/> is in use, the alternative server will need to present a certificate
   for the origin's host name, not that of the alternative. Likewise, the Host
   header field is still derived from the origin, not the alternative service (just as it
   would if a CNAME were being used).
</t>
<t>
  The changes &MAY;, however, be made visible in debugging tools, consoles, etc.
</t>
<t>
  Formally, an alternative service is identified by the combination of:
  <list style="symbols">
    <t>An Application Layer Protocol Negotiation (ALPN) protocol, as per
    <xref target="I-D.ietf-tls-applayerprotoneg"/></t>
    <t>A host, as per <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/></t>
    <t>A port, as per <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/></t>
  </list>
</t>
<t>
   Additionally, each alternative service &MUST; have:
  <list style="symbols">
    <t>A freshness lifetime, expressed in seconds; see <xref target="caching"/></t>
  </list>
</t>
<t>
   There are many ways that a client could discover the alternative service(s)
   associated with an origin.
</t>

<section title="Host Authentication" anchor="host_auth">
<t>
   Clients &MUST-NOT; use alternative services with a host other than the origin's
   without strong server authentication; this mitigates the attack described in
   <xref target="host_security"/>. One way to achieve this is for the alternative to use TLS
   with a certificate that is valid for that origin.
</t>
<t>
   For example, if the origin's host is "www.example.com" and an alternative is
   offered on "other.example.com" with the "h2" protocol, and the certificate
   offered is valid for "www.example.com", the client can use the alternative.
   However, if "other.example.com" is offered with the "h2c" protocol, the client
   cannot use it, because there is no mechanism in that protocol to establish
   strong server authentication.
</t>
<t>
   Furthermore, this means that the HTTP Host header field and the SNI information
   provided in TLS by the client will be that of the origin, not the alternative.
</t>
</section>

<section title="Alternative Service Caching" anchor="caching" >
<t>
   Mechanisms for discovering alternative services can associate a freshness
   lifetime with them; for example, the Alt-Svc header field uses the "ma"
   parameter.
</t>
<t>
   Clients &MAY; choose to use an alternative service instead of the origin at any
   time when it is considered fresh; see <xref target="switching"/> for specific
   recommendations.
</t>
<t>
   Clients with existing connections to alternative services are not required to
   fall back to the origin when its freshness lifetime ends; i.e., the caching
   mechanism is intended for limiting how long an alternative service can be used
   for establishing new requests, not limiting the use of existing ones.
</t>
<t>
   To mitigate risks associated with caching compromised values (see
   <xref target="host_security"/> for details), user agents &SHOULD; examine cached alternative
   services when they detect a change in network configuration, and remove any
   that could be compromised (for example, those whose association with the trust
   root is questionable). UAs that do not have a means of detecting network
   changes &SHOULD; place an upper bound on their lifetime.
</t>
</section>

<section title="Requiring Server Name Indication" anchor="requiring-server-name-indication">
<t>
   A client &MUST; only use a TLS-based alternative service if the client also
   supports TLS Server Name Indication (SNI) (<xref target="RFC6066" x:sec="3" x:fmt=","/>).
   This supports the conservation of IP addresses on the alternative service host.
</t>
</section>

<section title="Using Alternative Services" anchor="switching">
<t>
   By their nature, alternative services are optional; clients are not required to
   use them. However, it is advantageous for clients to behave in a predictable
   way when they are used by servers (e.g., for load balancing).
</t>
<t>
   Therefore, if a client becomes aware of an alternative service, the client
   &SHOULD; use that alternative service for all requests to the associated origin
   as soon as it is available, provided that the security properties of the
   alternative service protocol are desirable, as compared to the existing
   connection.
</t>
<t>
   When a client uses an alternate service, it &MUST; emit the Service header field
   (<xref target="service"/>) on every request using that alternate service.
</t>
<t>
   The client is not required to block requests; the origin's connection can be
   used until the alternative connection is established. However, if the security
   properties of the existing connection are weak (e.g. cleartext HTTP/1.1) then
   it might make sense to block until the new connection is fully available in
   order to avoid information leakage.
</t>
<t>
   Furthermore, if the connection to the alternative service fails or is
   unresponsive, the client &MAY; fall back to using the origin. Note, however, that
   this could be the basis of a downgrade attack, thus losing any enhanced
   security properties of the alternative service.
</t>
</section>
</section>

<section title="The Alt-Svc HTTP Header Field" anchor="alt-svc">
<t>
   An HTTP(S) origin server can advertise the availability of alternative services
   to clients by adding an Alt-Svc header field to responses.
</t>
<figure>
  <artwork type="abnf2616">
Alt-Svc     = 1#( alternative *( OWS ";" OWS parameter ) )
alternative = protocol-id "=" port
protocol-id = token ; percent-encoded ALPN protocol identifier
</artwork>
</figure>
<t>
   ALPN protocol names are octet sequences with no
   additional constraints on format.<!-- besides length?-->
   Octets not allowed in tokens (<xref target="HTTP-p1" x:fmt="," x:rel="#field.components"/>)
   &MUST; be percent-encoded as per <xref target="RFC3986" x:fmt="of" x:sec="2.1"/>.
   Consequently, the octet representing the percent character "%" (hex 25) &MUST;
   be percent-encoded as well.
</t>
<t>
   In order to have precisely one way to represent any ALPN protocol name, the following
   additional constraints apply:
   <list style="numbers">
    <t>
      Octets in the ALPN protocol &MUST-NOT; be percent-encoded if they are valid 
      token characters except "%", and
    </t>
    <t>
      When using percent-encoding, uppercase hex digits &MUST; be used.
    </t>
   </list>
</t>
<t>
  With these constraints, recipients can apply simple string comparison to
  match protocol identifiers.
</t>
<figure>
  <preamble>For example:</preamble>
   <artwork type="example">
Alt-Svc: http2=8000
</artwork>
<postamble>
   This indicates that the "http2" protocol on the same host using the
   indicated port (in this case, 8000).
</postamble>
</figure>
<texttable style="all" align="left">
  <preamble>Examples for protocol name escaping:</preamble>
  <ttcol>ALPN protocol name</ttcol>
  <ttcol>protocol-id</ttcol>
  <ttcol>Note</ttcol>
  
  <c>http2</c>
  <c>http2</c>
  <c>No escaping needed</c>
  
  <c>w=x:y#z</c>
  <c>w%3Dx%3Ay#z</c>
  <c>"=" and ":" escaped</c>

  <c>x%y</c>
  <c>x%25y</c>
  <c>"%" needs escaping</c>
</texttable>
<t>
   Alt-Svc &MAY; occur in any HTTP response message, regardless of the status code.
</t>
<t>
   Alt-Svc does not allow advertisement of alternative services on other hosts, to
   protect against various header-based attacks.
</t>
<figure>
  <preamble>It can, however, have multiple values:</preamble>
  <artwork type="example">
Alt-Svc: h2c=8000, h2=443
</artwork>
</figure>
<t>
   The value(s) advertised by Alt-Svc can be used by clients to open a new
   connection to one or more alternative services immediately, or simultaneously
   with subsequent requests on the same connection.
</t>
<t>
   Intermediaries &MUST-NOT; change or append Alt-Svc field values.
</t>

<section title="Caching Alt-Svc Header Field Values" anchor="caching-alt-svc-header-field-values">
<t>
   When an alternative service is advertised using Alt-Svc, it is considered fresh
   for 24 hours from generation of the message. This can be modified with the 'ma'
   (max-age) parameter;
</t>
<figure>
  <artwork type="example">
Alt-Svc: h2=443;ma=3600
</artwork>
</figure>
<t>
   which indicates the number of seconds since the response was generated the
   alternative service is considered fresh for.
</t>
<figure>
  <artwork type="abnf2616">
ma = delta-seconds
</artwork></figure>
<t>
   See <xref target="HTTP-p6" x:rel="#age.calculations" x:fmt="of"/> for details of determining
   response age.
</t>
<figure>
  <preamble>For example, a response:</preamble>
  <artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
HTTP/1.1 200 OK
Content-Type: text/html
Cache-Control: 600
Age: 30
Alt-Svc: h2c=8000; ma=60
</artwork>
<postamble>
   indicates that an alternative service is available and usable for the next 60
   seconds. However, the response has already been cached for 30 seconds (as per
   the Age header field value), so therefore the alternative service is only fresh
   for the 30 seconds from when this response was received, minus estimated
   transit time.
</postamble>
</figure>
<t>
   When an Alt-Svc response header field is received from an origin, its value
   invalidates and replaces all cached alternative services for that origin.
</t>
<t>
   See <xref target="caching"/> for general requirements on caching alternative services.
</t>
<t>
   Note that the freshness lifetime for HTTP caching (here, 600 seconds) does not
   affect caching of Alt-Svc values.
</t>
</section>
</section>

<section title="The Service HTTP Header Field" anchor="service">
<t>
   The Service HTTP header field is used in requests to indicate the identity of the 
   alternate service in use, just as the Host header field identifies the host and port
   of the origin.
</t>
<figure>
<artwork type="abnf2616">
Service = uri-host [ ":" port ]
</artwork>
</figure>
<t>
   Service is intended to allow alternate services to detect loops, differentiate
   traffic for purposes of load balancing, and generally to ensure that it is
   possible to identify the intended destination of traffic, since introducing
   this information after a protocol is in use has proven to be problematic.
</t>
<t>
   When using an Alternate Service, clients &MUST; include a Service header in all 
   requests.
</t>
<figure>
  <preamble>For example:</preamble>
  <artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
GET /thing
Host: origin.example.com
Service: alternate.example.net
User-Agent: Example/1.0
</artwork>
</figure>
</section>

<section title="The 421 Not Authoritative HTTP Status Code" anchor="status">
<t>
   The 421 (Not Authoritative) status code indicates that the current origin
   server (usually, but not always an alternative service; see <xref target="alternative"/>) is
   not authoritative for the requested resource, in the sense of
   <xref target="HTTP-p1" x:rel="#establishing.authority" x:fmt=","/>.
</t>
<t>
   Clients receiving 421 (Not Authoritative) from an alternative service &MUST;
   remove the corresponding entry from its alternative service cache (see
   <xref target="caching"/>) for that origin. Regardless of the idempotency of the request
   method, they &MAY; retry the request, either at another alternative server, or at
   the origin.
</t>
<t>
   421 (Not Authoritative) &MAY; carry an Alt-Svc header field.
</t>
<t>
   This status code &MUST-NOT; be generated by proxies.
</t>
<t>
   A 421 response is cacheable by default; i.e., unless otherwise indicated by the
   method definition or explicit cache controls (see <xref target="HTTP-p6" x:rel="#heuristic.freshness" x:fmt="of"/>).
</t>
</section>

<section title="IANA Considerations" anchor="iana-considerations" >

<section anchor="the-alt-svc-message-header-field" title="The Alt-Svc Message Header Field">
<t>
   This document registers Alt-Svc in the Permanent Message Header Registry
   <xref target="RFC3864"/>.
</t>
<t>
  <list style="symbols">
    <t>Header Field Name: Alt-Svc</t>
    <t>Application Protocol: http</t>
    <t>Status: standard</t>
    <t>Author/Change Controller: IETF</t>
    <t>Specification Document: [this document]</t>
    <t>Related Information: </t>
  </list>
</t>
</section>

<section title="The Service Message Header Field" anchor="the-service-message-header-field" >
<t>
   This document registers Alt-Svc in the Permanent Message Header Registry
   <xref target="RFC3864"/>.
</t>
<t>
  <list style="symbols">
    <t>Header Field Name: Service</t>
    <t>Application Protocol: http</t>
    <t>Status: standard</t>
    <t>Author/Change Controller: IETF</t>
    <t>Specification Document: [this document]</t>
    <t>Related Information: </t>
  </list>
</t>
</section>

<section title="The 421 Not Authoritative HTTP Status Code" anchor="status.code.registration">
<t>
   This document registers the 421 (Not Authoritative) HTTP Status code
   in the Hypertext Transfer Protocol (HTTP) Status Code Registry
   (<xref target="HTTP-p2" x:fmt="," x:rel="#status.code.registry"/>).
</t>
<t>
  <list style="empty">
    <t>Status Code: 421</t>
    <t>Short Description: Not Authoritative</t>
    <t>Specification: <xref target="status"/> of this document</t>
  </list>
</t>
</section>

</section>

<section title="Security Considerations" anchor="security-considerations">

<section title="Changing Ports" anchor="changing-ports" >
<t>
   Using an alternative service implies accessing an origin's resources on an
   alternative port, at a minimum. An attacker that can inject alternative services
   and listen at the advertised port is therefore able to hijack an origin.
</t>
<t>
   For example, an attacker that can add HTTP response header fields can redirect
   traffic to a different port on the same host using the Alt-Svc header field; if
   that port is under the attacker's control, they can thus masquerade as the HTTP
   server.
</t>
<t>
   This risk can be mitigated by restricting the ability to advertise alternative
   services, and restricting who can open a port for listening on that host.
</t>
</section>

<section title="Changing Hosts" anchor="host_security">
<t>
   When the host is changed due to the use of an alternative service, it presents
   an opportunity for attackers to hijack communication to an origin.
</t>
<t>
   For example, if an attacker can convince a user agent to send all traffic for
   "innocent.example.org" to "evil.example.com" by successfully associating it as
   an alternative service, they can masquerade as that origin. This can be done
   locally (see mitigations above) or remotely (e.g., by an intermediary as a
   man-in-the-middle attack).
</t>
<t>
   This is the reason for the requirement in <xref target="host_auth"/> that any alternative
   service with a host different to the origin's be strongly authenticated with
   the origin's identity; i.e., presenting a certificate for the origin proves
   that the alternative service is authorized to serve traffic for the origin.
</t>
<t>
   However, this authorization is only as strong as the method used to
   authenticate the alternative service. In particular, there are well-known
   exploits to make an attacker's certificate appear as legitimate.
</t>
<t>
   Alternative services could be used to persist such an attack; for example, an
   intermediary could man-in-the-middle TLS-protected communication to a target,
   and then direct all traffic to an alternative service with a large freshness
   lifetime, so that the user agent still directs traffic to the attacker even when
   not using the intermediary.
</t>
<t>
   As a result, there is a requirement in <xref target="caching"/> to examine cached alternative
   services when a network change is detected.
</t>
</section>

<section title="Changing Protocols" anchor="changing-protocols">
<t>
   When the ALPN protocol is changed due to the use of an alternative service, the
   security properties of the new connection to the origin can be different from
   that of the "normal" connection to the origin, because the protocol identifier
   itself implies this.
</t>
<t>
   For example, if a "https://" URI had a protocol advertised that does not use
   some form of end-to-end encryption (most likely, TLS), it violates the
   expectations for security that the URI scheme implies.
</t>
<t>
   Therefore, clients cannot blindly use alternative services, but instead evaluate
   the option(s) presented to assure that security requirements and expectations
   (of specifications, implementations and end users) are met.
</t>
</section>
</section>

<section title="Acknowledgements" anchor="acknowledgements" >
<t>
  Thanks to Eliot Lear, Stephen Farrell, Guy Podjarny, Stephen Ludin, Erik
  Nygren, Paul Hoffman, Adam Langley, Will Chan and Richard Barnes for their
  feedback and suggestions.
</t>
<t>
  The Alt-Svc header field was influenced by the design of the 
  Alternative-Protocol header field in SPDY.
</t>
</section>

  </middle>
  
  <back>

<references title="Normative References">

<reference anchor="RFC2119">
  <front>
    <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
    <author initials="S." surname="Bradner" fullname="Scott Bradner">
      <organization>Harvard University</organization>
    </author>
    <date year="1997" month="March"/>
  </front>
  <seriesInfo name="BCP" value="14"/>
  <seriesInfo name="RFC" value="2119"/>
</reference>

<reference anchor="RFC3986">
  <front>
    <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
    </author>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
      <organization abbrev="Day Software">Day Software</organization>
    </author>
    <author initials="L." surname="Masinter" fullname="Larry Masinter">
      <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
    </author>
    <date year="2005" month="January"/>
  </front>
  <seriesInfo name="STD" value="66"/>
  <seriesInfo name="RFC" value="3986"/>
</reference>

<reference anchor="RFC5234">
  <front>
    <title>Augmented BNF for Syntax Specifications: ABNF</title>
    <author initials="D." surname="Crocker" fullname="D. Crocker"/>
    <author initials="P." surname="Overell" fullname="P. Overell"/>
    <date year="2008" month="January"/>
  </front>
  <seriesInfo name="STD" value="68"/>
  <seriesInfo name="RFC" value="5234"/>
</reference>

<reference anchor="RFC6066">
  <front>
    <title>Transport Layer Security (TLS) Extensions: Extension Definitions</title>
    <author initials="D." surname="Eastlake" fullname="D. Eastlake"/>
    <date year="2011" month="January"/>
  </front>
  <seriesInfo name="RFC" value="6066"/>
</reference>

<reference anchor="RFC6454">
  <front>
    <title>The Web Origin Concept</title>
    <author initials="A." surname="Barth" fullname="A. Barth"/>
    <date year="2011" month="December"/>
  </front>
  <seriesInfo name="RFC" value="6454"/>
</reference>

<reference anchor="I-D.ietf-tls-applayerprotoneg">
  <front>
    <title>Transport Layer Security (TLS) Application Layer Protocol Negotiation Extension</title>
    <author initials="S." surname="Friedl" fullname="Stephan Friedl"/>
    <author initials="A." surname="Popov" fullname="Andrey Popov"/>
    <author initials="A." surname="Langley" fullname="Adam Langley"/>
    <author initials="S." surname="Emile" fullname="Stephan Emile"/>
    <date month="March" year="2014"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-tls-applayerprotoneg-05"/>
</reference>

<reference anchor="HTTP-p1">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="February" year="2014" />
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-26" />
  <x:source href="refs/draft-ietf-httpbis-p1-messaging-26.xml"
            basename="https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/26/p1-messaging"/>
</reference>

<reference anchor="HTTP-p6">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Caching</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author fullname="Mark Nottingham" initials="M." role="editor" surname="Nottingham">
      <organization>Akamai</organization>
      <address><email>mnot@mnot.net</email></address>
    </author>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="February" year="2014" />
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-26"/>
  <x:source href="refs/draft-ietf-httpbis-p6-cache-26.xml"
            basename="https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/26/p6-cache"/>
</reference>

</references>

<references title="Informative References">

<reference anchor="RFC3864">
  <front>
    <title>Registration Procedures for Message Header Fields</title>
    <author initials="G." surname="Klyne" fullname="G. Klyne"/>
    <author initials="M." surname="Nottingham" fullname="M. Nottingham"/>
    <author initials="J." surname="Mogul" fullname="J. Mogul"/>
    <date year="2004" month="September"/>
  </front>
  <seriesInfo name="BCP" value="90"/>
  <seriesInfo name="RFC" value="3864"/>
</reference>

<reference anchor="RFC5246">
  <front>
    <title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
    <author initials="T." surname="Dierks" fullname="T. Dierks"/>
    <author initials="E." surname="Rescorla" fullname="E. Rescorla"/>
    <date year="2008" month="August"/>
  </front>
  <seriesInfo name="RFC" value="5246"/>
</reference>

<reference anchor="HTTP-p2">
  <front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
      <address><email>fielding@gbiv.com</email></address>
    </author>
    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
      <organization abbrev="greenbytes">greenbytes GmbH</organization>
      <address><email>julian.reschke@greenbytes.de</email></address>
    </author>
    <date month="February" year="2014" />
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-26" />
  <x:source href="refs/draft-ietf-httpbis-p2-semantics-26.xml"
            basename="https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/26/p2-semantics"/>
</reference>

<reference anchor="HTTP2">
  <front>
    <title>Hypertext Transfer Protocol version 2</title>
    <author initials="M." surname="Belshe" fullname="Mike Belshe"/>
    <author initials="R." surname="Peon" fullname="Roberto Peon"/>
    <author initials="M." surname="Thomson" fullname="Martin Thomson" role="editor"/>
    <date month="April" year="2014"/>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-http2-12"/>
</reference>

</references>

<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">

<section title="Since draft-nottingham-httpbis-alt-svc-05" anchor="changes.since.draft-nottingham-httpbis-alt-svc-05">
<t>
  This is the first version after adoption of draft-nottingham-httpbis-alt-svc-05
  as Working Group work item. It only contains editorial changes.
</t>
</section>

<section title="Since draft-ietf-httpbis-alt-svc-00" anchor="changes.since.draft-ietf-httpbis-alt-svc-00">
<t>
  Selected 421 as proposed status code for "Not Authoritative".
</t>
<t>
  Changed header field syntax to use percent-encoding of ALPN protocol names
  (<eref target="https://github.com/http2/http2-spec/issues/446"/>).
</t>
</section>

<section title="Since draft-ietf-httpbis-alt-svc-01" anchor="changes.since.draft-ietf-httpbis-alt-svc-01">
<t>
  None yet.
</t>
</section>

</section>

  </back>
</rfc>