rfc9460.original   rfc9460.txt 
DNSOP Working Group B. Schwartz Internet Engineering Task Force (IETF) B. Schwartz
Internet-Draft Google Request for Comments: 9460 Meta Platforms, Inc.
Intended status: Standards Track M. Bishop Category: Standards Track M. Bishop
Expires: 12 September 2023 E. Nygren ISSN: 2070-1721 E. Nygren
Akamai Technologies Akamai Technologies
11 March 2023 November 2023
Service binding and parameter specification via the DNS (DNS SVCB and Service Binding and Parameter Specification via the DNS (SVCB and HTTPS
HTTPS RRs) Resource Records)
draft-ietf-dnsop-svcb-https-12
Abstract Abstract
This document specifies the "SVCB" and "HTTPS" DNS resource record This document specifies the "SVCB" ("Service Binding") and "HTTPS"
(RR) types to facilitate the lookup of information needed to make DNS resource record (RR) types to facilitate the lookup of
connections to network services, such as for HTTP origins. SVCB information needed to make connections to network services, such as
records allow a service to be provided from multiple alternative for HTTP origins. SVCB records allow a service to be provided from
endpoints, each with associated parameters (such as transport multiple alternative endpoints, each with associated parameters (such
protocol configuration), and are extensible to support future uses as transport protocol configuration), and are extensible to support
(such as keys for encrypting the TLS ClientHello). They also enable future uses (such as keys for encrypting the TLS ClientHello). They
aliasing of apex domains, which is not possible with CNAME. The also enable aliasing of apex domains, which is not possible with
HTTPS RR is a variation of SVCB for use with HTTP [HTTP]. By CNAME. The HTTPS RR is a variation of SVCB for use with HTTP (see
providing more information to the client before it attempts to RFC 9110, "HTTP Semantics"). By providing more information to the
establish a connection, these records offer potential benefits to client before it attempts to establish a connection, these records
both performance and privacy. offer potential benefits to both performance and privacy.
TO BE REMOVED: This document is being collaborated on in Github at:
https://github.com/MikeBishop/dns-alt-svc
(https://github.com/MikeBishop/dns-alt-svc). The most recent working
version of the document, open issues, etc. should all be available
there. The authors (gratefully) accept pull requests.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
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working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at https://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
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time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc9460.
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This Internet-Draft will expire on 12 September 2023.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
1.1. Goals of the SVCB RR . . . . . . . . . . . . . . . . . . 5 1.1. Goals
1.2. Overview of the SVCB RR . . . . . . . . . . . . . . . . . 5 1.2. Overview of the SVCB RR
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.3. Terminology
2. The SVCB record type . . . . . . . . . . . . . . . . . . . . 7 2. The SVCB Record Type
2.1. Zone file presentation format . . . . . . . . . . . . . . 8 2.1. Zone-File Presentation Format
2.2. RDATA wire format . . . . . . . . . . . . . . . . . . . . 9 2.2. RDATA Wire Format
2.3. SVCB query names . . . . . . . . . . . . . . . . . . . . 10 2.3. SVCB Query Names
2.4. Interpretation . . . . . . . . . . . . . . . . . . . . . 10 2.4. Interpretation
2.4.1. SvcPriority . . . . . . . . . . . . . . . . . . . . . 11 2.4.1. SvcPriority
2.4.2. AliasMode . . . . . . . . . . . . . . . . . . . . . . 11 2.4.2. AliasMode
2.4.3. ServiceMode . . . . . . . . . . . . . . . . . . . . . 12 2.4.3. ServiceMode
2.5. Special handling of "." in TargetName . . . . . . . . . . 13 2.5. Special Handling of "." in TargetName
2.5.1. AliasMode . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1. AliasMode
2.5.2. ServiceMode . . . . . . . . . . . . . . . . . . . . . 13 2.5.2. ServiceMode
3. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 13 3. Client Behavior
3.1. Handling resolution failures . . . . . . . . . . . . . . 15 3.1. Handling Resolution Failures
3.2. Clients using a Proxy . . . . . . . . . . . . . . . . . . 15 3.2. Clients Using a Proxy
4. DNS Server Behavior . . . . . . . . . . . . . . . . . . . . . 16 4. DNS Server Behavior
4.1. Authoritative servers . . . . . . . . . . . . . . . . . . 16 4.1. Authoritative Servers
4.2. Recursive resolvers . . . . . . . . . . . . . . . . . . . 17 4.2. Recursive Resolvers
4.2.1. DNS64 . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2.1. DNS64
4.3. General requirements . . . . . . . . . . . . . . . . . . 18 4.3. General Requirements
4.4. EDNS Client Subnet (ECS) . . . . . . . . . . . . . . . . 18 4.4. EDNS Client Subnet (ECS)
5. Performance optimizations . . . . . . . . . . . . . . . . . . 19 5. Performance Optimizations
5.1. Optimistic pre-connection and connection reuse . . . . . 19 5.1. Optimistic Pre-connection and Connection Reuse
5.2. Generating and using incomplete responses . . . . . . . . 20 5.2. Generating and Using Incomplete Responses
6. SVCB-compatible . . . . . . . . . . . . . . . . . . . . . . . 20 6. SVCB-Compatible RR Types
7. Initial SvcParamKeys . . . . . . . . . . . . . . . . . . . . 21 7. Initial SvcParamKeys
7.1. "alpn" and "no-default-alpn" . . . . . . . . . . . . . . 21 7.1. "alpn" and "no-default-alpn"
7.1.1. Representation . . . . . . . . . . . . . . . . . . . 22 7.1.1. Representation
7.1.2. Use . . . . . . . . . . . . . . . . . . . . . . . . . 22 7.1.2. Use
7.2. "port" . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.2. "port"
7.3. "ipv4hint" and "ipv6hint" . . . . . . . . . . . . . . . . 24 7.3. "ipv4hint" and "ipv6hint"
7.4. "mandatory" . . . . . . . . . . . . . . . . . . . . . . . 25 7.4. "mandatory"
8. ServiceMode RR compatibility and mandatory keys . . . . . . . 25 8. ServiceMode RR Compatibility and Mandatory Keys
9. Using Service Bindings with HTTP . . . . . . . . . . . . . . 26 9. Using Service Bindings with HTTP
9.1. Query names for HTTPS RRs . . . . . . . . . . . . . . . . 26 9.1. Query Names for HTTPS RRs
9.2. Comparison with Alt-Svc . . . . . . . . . . . . . . . . . 27 9.2. Comparison with Alt-Svc
9.2.1. ALPN usage . . . . . . . . . . . . . . . . . . . . . 27 9.2.1. ALPN Usage
9.2.2. Untrusted channel . . . . . . . . . . . . . . . . . . 27 9.2.2. Untrusted Channels
9.2.3. Cache lifetime . . . . . . . . . . . . . . . . . . . 27 9.2.3. Cache Lifetime
9.2.4. Granularity . . . . . . . . . . . . . . . . . . . . . 28 9.2.4. Granularity
9.3. Interaction with Alt-Svc . . . . . . . . . . . . . . . . 28 9.3. Interaction with Alt-Svc
9.4. Requiring Server Name Indication . . . . . . . . . . . . 29 9.4. Requiring Server Name Indication
9.5. HTTP Strict Transport Security . . . . . . . . . . . . . 29 9.5. HTTP Strict Transport Security (HSTS)
9.6. Use of HTTPS RRs in other protocols . . . . . . . . . . . 30 9.6. Use of HTTPS RRs in Other Protocols
10. Zone Structures . . . . . . . . . . . . . . . . . . . . . . . 30 10. Zone Structures
10.1. Structuring zones for flexibility . . . . . . . . . . . 31 10.1. Structuring Zones for Flexibility
10.2. Structuring zones for performance . . . . . . . . . . . 31 10.2. Structuring Zones for Performance
10.3. Operational considerations . . . . . . . . . . . . . . . 32 10.3. Operational Considerations
10.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 32 10.4. Examples
10.4.1. Protocol enhancements . . . . . . . . . . . . . . . 32 10.4.1. Protocol Enhancements
10.4.2. Apex aliasing . . . . . . . . . . . . . . . . . . . 32 10.4.2. Apex Aliasing
10.4.3. Parameter binding . . . . . . . . . . . . . . . . . 33 10.4.3. Parameter Binding
10.4.4. Multi-CDN . . . . . . . . . . . . . . . . . . . . . 33 10.4.4. Multi-CDN Configuration
10.4.5. Non-HTTP uses . . . . . . . . . . . . . . . . . . . 35 10.4.5. Non-HTTP Uses
11. Interaction with other standards . . . . . . . . . . . . . . 36 11. Interaction with Other Standards
12. Security Considerations . . . . . . . . . . . . . . . . . . . 36 12. Security Considerations
13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 37 13. Privacy Considerations
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 14. IANA Considerations
14.1. SVCB RRType . . . . . . . . . . . . . . . . . . . . . . 37 14.1. SVCB RR Type
14.2. HTTPS RRType . . . . . . . . . . . . . . . . . . . . . . 37 14.2. HTTPS RR Type
14.3. New registry for Service Parameters . . . . . . . . . . 38 14.3. New Registry for Service Parameters
14.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . 38 14.3.1. Procedure
14.3.2. Initial contents . . . . . . . . . . . . . . . . . . 39 14.3.2. Initial Contents
14.4. Other registry updates . . . . . . . . . . . . . . . . . 41 14.4. Other Registry Updates
15. Acknowledgments and Related Proposals . . . . . . . . . . . . 41 15. References
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 15.1. Normative References
16.1. Normative References . . . . . . . . . . . . . . . . . . 41 15.2. Informative References
16.2. Informative References . . . . . . . . . . . . . . . . . 44 Appendix A. Decoding Text in Zone Files
Appendix A. Decoding text in zone files . . . . . . . . . . . . 45 A.1. Decoding a Comma-Separated List
A.1. Decoding a comma-separated list . . . . . . . . . . . . . 46 Appendix B. HTTP Mapping Summary
Appendix B. HTTP Mapping Summary . . . . . . . . . . . . . . . . 47 Appendix C. Comparison with Alternatives
Appendix C. Comparison with alternatives . . . . . . . . . . . . 48 C.1. Differences from the SRV RR Type
C.1. Differences from the SRV RR type . . . . . . . . . . . . 48 C.2. Differences from the Proposed HTTP Record
C.2. Differences from the proposed HTTP record . . . . . . . . 48 C.3. Differences from the Proposed ANAME Record
C.3. Differences from the proposed ANAME record . . . . . . . 48 C.4. Comparison with Separate RR Types for AliasMode and
C.4. Comparison with separate RR types for AliasMode and ServiceMode
ServiceMode . . . . . . . . . . . . . . . . . . . . . . . 49 Appendix D. Test Vectors
Appendix D. Test vectors . . . . . . . . . . . . . . . . . . . . 49 D.1. AliasMode
D.1. AliasMode . . . . . . . . . . . . . . . . . . . . . . . . 49 D.2. ServiceMode
D.2. ServiceMode . . . . . . . . . . . . . . . . . . . . . . . 49 D.3. Failure Cases
D.3. Failure cases . . . . . . . . . . . . . . . . . . . . . . 54 Acknowledgments and Related Proposals
Appendix E. Change history . . . . . . . . . . . . . . . . . . . 55 Authors' Addresses
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60
1. Introduction 1. Introduction
The SVCB ("Service Binding") and HTTPS RRs provide clients with The SVCB ("Service Binding") and HTTPS resource records (RRs) provide
complete instructions for access to a service. This information clients with complete instructions for access to a service. This
enables improved performance and privacy by avoiding transient information enables improved performance and privacy by avoiding
connections to a suboptimal default server, negotiating a preferred transient connections to a suboptimal default server, negotiating a
protocol, and providing relevant public keys. preferred protocol, and providing relevant public keys.
For example, HTTP clients currently resolve only A and/or AAAA For example, HTTP clients currently resolve only A and/or AAAA
records for the origin hostname, learning only its IP addresses. If records for the origin hostname, learning only its IP addresses. If
an HTTP client learns more about the origin before connecting, it may an HTTP client learns more about the origin before connecting, it may
be able to upgrade "http" URLs to "https", enable HTTP/3 or Encrypted be able to upgrade "http" URLs to "https", enable HTTP/3 or Encrypted
ClientHello [ECH], or switch to an operationally preferable endpoint. ClientHello [ECH], or switch to an operationally preferable endpoint.
It is highly desirable to minimize the number of round-trips and It is highly desirable to minimize the number of round trips and
lookups required to learn this additional information. lookups required to learn this additional information.
The SVCB and HTTPS RRs also help when the operator of a service The SVCB and HTTPS RRs also help when the operator of a service
wishes to delegate operational control to one or more other domains, wishes to delegate operational control to one or more other domains,
e.g. delegating the origin "https://example.com" to a service e.g., aliasing the origin "https://example.com" to a service operator
operator endpoint at "svc.example.net". While this case can endpoint at "svc.example.net". While this case can sometimes be
sometimes be handled by a CNAME, that does not cover all use-cases. handled by a CNAME, that does not cover all use cases. CNAME is also
CNAME is also inadequate when the service operator needs to provide a inadequate when the service operator needs to provide a bound
bound collection of consistent configuration parameters through the collection of consistent configuration parameters through the DNS
DNS (such as network location, protocol, and keying information). (such as network location, protocol, and keying information).
This document first describes the SVCB RR as a general-purpose This document first describes the SVCB RR as a general-purpose RR
resource record that can be applied directly and efficiently to a that can be applied directly and efficiently to a wide range of
wide range of services (Section 2). It also describes the rules for services (Section 2). It also describes the rules for defining other
defining other SVCB-compatible RR types (Section 6), starting with SVCB-compatible RR types (Section 6), starting with the HTTPS RR type
the HTTPS RR type (Section 9), which provides improved efficiency and (Section 9), which provides improved efficiency and convenience with
convenience with HTTP by avoiding the need for an Attrleaf label HTTP by avoiding the need for an Attrleaf label [Attrleaf]
[Attrleaf] (Section 9.1). (Section 9.1).
The SVCB RR has two modes: 1) "AliasMode", which simply delegates The SVCB RR has two modes: 1) "AliasMode", which simply delegates
operational control for a resource; 2) "ServiceMode", which binds operational control for a resource and 2) "ServiceMode", which binds
together configuration information for a service endpoint. together configuration information for a service endpoint.
ServiceMode provides additional key=value parameters within each ServiceMode provides additional key=value parameters within each
RDATA set. RDATA set.
1.1. Goals of the SVCB RR 1.1. Goals
The goal of the SVCB RR is to allow clients to resolve a single The goal of the SVCB RR is to allow clients to resolve a single
additional DNS RR in a way that: additional DNS RR in a way that:
* Provides alternative endpoints that are authoritative for the * Provides alternative endpoints that are authoritative for the
service, along with parameters associated with each of these service, along with parameters associated with each of these
endpoints. endpoints.
* Does not assume that all alternative endpoints have the same * Does not assume that all alternative endpoints have the same
parameters or capabilities, or are even operated by the same parameters or capabilities, or are even operated by the same
entity. This is important, as DNS does not provide any way to tie entity. This is important, as DNS does not provide any way to tie
together multiple RRSets for the same name. For example, if together multiple RRsets for the same name. For example, if
www.example.com is a CNAME alias that switches between one of "www.example.com" is a CNAME alias that switches between one of
three CDNs or hosting environments, successive queries for that three Content Delivery Networks (CDNs) or hosting environments,
name may return records that correspond to different environments. successive queries for that name may return records that
correspond to different environments.
* Enables CNAME-like functionality at a zone apex (such as * Enables CNAME-like functionality at a zone apex (such as
"example.com") for participating protocols, and generally enables "example.com") for participating protocols and generally enables
delegation of operational authority for an origin within the DNS extending operational authority for a service identified by a
to an alternate name. domain name to other instances with alternate names.
Additional goals specific to HTTPS RRs and the HTTP use-cases Additional goals specific to HTTPS RRs and the HTTP use cases
include: include:
* Connect directly to HTTP/3 (QUIC transport) alternative endpoints * Connecting directly to HTTP/3 (QUIC transport) alternative
[HTTP3] endpoints [HTTP/3].
* Support non-default TCP and UDP ports * Supporting non-default TCP and UDP ports.
* Enable SRV-like benefits (e.g. apex delegation, as mentioned * Enabling SRV-like benefits (e.g., apex aliasing, as mentioned
above) for HTTP, where SRV [SRV] has not been widely adopted above) for HTTP, where SRV [SRV] has not been widely adopted.
* Provide an HSTS-like indication [HSTS] signaling that the "https" * Providing an indication signaling that the "https" scheme should
scheme should be used instead of "http" for all HTTP requests to be used instead of "http" for all HTTP requests to this host and
this host and port (see Section 9.5). port, similar to HTTP Strict Transport Security [HSTS] (see
Section 9.5).
* Enable the conveyance of Encrypted ClientHello [ECH] keys * Enabling the conveyance of Encrypted ClientHello keys [ECH]
associated with an alternative endpoint. associated with an alternative endpoint.
1.2. Overview of the SVCB RR 1.2. Overview of the SVCB RR
This subsection briefly describes the SVCB RR with forward references This subsection briefly describes the SVCB RR with forward references
to the full exposition of each component. (As mentioned above, this to the full exposition of each component. (As discussed in
all applies equally to the HTTPS RR which shares the same encoding, Section 6, this all applies equally to the HTTPS RR, which shares the
format, and high-level semantics.) same encoding, format, and high-level semantics.)
The SVCB RR has two modes: AliasMode (Section 2.4.2), which aliases a
name to another name, and ServiceMode (Section 2.4.3), which provides The SVCB RR has two modes: 1) AliasMode (Section 2.4.2), which
connection information bound to a service endpoint domain. Placing aliases a name to another name and 2) ServiceMode (Section 2.4.3),
both forms in a single RR type allows clients to fetch the relevant which provides connection information bound to a service endpoint
information with a single query (Section 2.3). domain. Placing both forms in a single RR type allows clients to
fetch the relevant information with a single query (Section 2.3).
The SVCB RR has two required fields and one optional field. The The SVCB RR has two required fields and one optional field. The
fields are: fields are:
1. SvcPriority (Section 2.4.1): The priority of this record SvcPriority (Section 2.4.1): The priority of this record (relative
(relative to others, with lower values preferred). A value of 0 to others, with lower values preferred). A value of 0 indicates
indicates AliasMode. AliasMode.
2. TargetName: The domain name of either the alias target (for TargetName: The domain name of either the alias target (for
AliasMode) or the alternative endpoint (for ServiceMode). AliasMode) or the alternative endpoint (for ServiceMode).
3. SvcParams (optional): A list of key=value pairs describing the SvcParams (optional): A list of key=value pairs describing the
alternative endpoint at TargetName (only used in ServiceMode and alternative endpoint at TargetName (only used in ServiceMode and
otherwise ignored). Described in Section 2.1. otherwise ignored). SvcParams are described in Section 2.1.
Cooperating DNS recursive resolvers will perform subsequent record Cooperating DNS recursive resolvers will perform subsequent record
resolution (for SVCB, A, and AAAA records) and return them in the resolution (for SVCB, A, and AAAA records) and return them in the
Additional Section of the response (Section 4.2). Clients either use Additional section of the response (Section 4.2). Clients either use
responses included in the additional section returned by the responses included in the Additional section returned by the
recursive resolver or perform necessary SVCB, A, and AAAA record recursive resolver or perform necessary SVCB, A, and AAAA record
resolutions (Section 3). DNS authoritative servers can attach in- resolutions (Section 3). DNS authoritative servers can attach in-
bailiwick SVCB, A, AAAA, and CNAME records in the Additional bailiwick SVCB, A, AAAA, and CNAME records in the Additional section
Section to responses for a SVCB query (Section 4.1). to responses for a SVCB query (Section 4.1).
In ServiceMode, the SvcParams of the SVCB RR provide an extensible In ServiceMode, the SvcParams of the SVCB RR provide an extensible
data model for describing alternative endpoints that are data model for describing alternative endpoints that are
authoritative for a service, along with parameters associated with authoritative for a service, along with parameters associated with
each of these alternative endpoints (Section 7). each of these alternative endpoints (Section 7).
For HTTP use-cases, the HTTPS RR (Section 9) enables many of the For HTTP use cases, the HTTPS RR (Section 9) enables many of the
benefits of Alt-Svc [AltSvc] without waiting for a full HTTP benefits of Alt-Svc [AltSvc] without waiting for a full HTTP
connection initiation (multiple roundtrips) before learning of the connection initiation (multiple round trips) before learning of the
preferred alternative, and without necessarily revealing the user's preferred alternative, and without necessarily revealing the user's
intended destination to all entities along the network path. intended destination to all entities along the network path.
1.3. Terminology 1.3. Terminology
Our terminology is based on the common case where the SVCB record is Terminology in this document is based on the common case where the
used to access a resource identified by a URI whose authority field SVCB record is used to access a resource identified by a URI whose
contains a DNS hostname as the host. authority field contains a DNS hostname as the host.
* The "service" is the information source identified by the * The "service" is the information source identified by the
authority and scheme of the URI, capable of providing access to authority and scheme of the URI, capable of providing access to
the resource. For "https" URIs, the "service" corresponds to an the resource. For "https" URIs, the "service" corresponds to an
"origin" [RFC6454]. "origin" [RFC6454].
* The "service name" is the host portion of the authority. * The "service name" is the host portion of the authority.
* The "authority endpoint" is the authority's hostname and a port * The "authority endpoint" is the authority's hostname and a port
number implied by the scheme or specified in the URI. number implied by the scheme or specified in the URI.
* An "alternative endpoint" is a hostname, port number, and other * An "alternative endpoint" is a hostname, port number, and other
associated instructions to the client on how to reach an instance associated instructions to the client on how to reach an instance
of service. of a service.
Additional DNS terminology intends to be consistent with [DNSTerm]. Additional DNS terminology intends to be consistent with [DNSTerm].
SVCB is a contraction of "service binding". The SVCB RR, HTTPS RR, SVCB is a contraction of "service binding". The SVCB RR, HTTPS RR,
and future RR types that share SVCB's formats and registry are and future RR types that share SVCB's formats and registry are
collectively known as SVCB-compatible RR types. The contraction collectively known as SVCB-compatible RR types. The contraction
"SVCB" is also used to refer to this system as a whole. "SVCB" is also used to refer to this system as a whole.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. The SVCB record type 2. The SVCB Record Type
The SVCB DNS resource record (RR) type (RR type 64) is used to locate The SVCB DNS RR type (RR type 64) is used to locate alternative
alternative endpoints for a service. endpoints for a service.
The algorithm for resolving SVCB records and associated address The algorithm for resolving SVCB records and associated address
records is specified in Section 3. records is specified in Section 3.
Other SVCB-compatible resource record types can also be defined as- Other SVCB-compatible RR types can also be defined as needed (see
needed (see Section 6). In particular, the HTTPS RR (RR type 65) Section 6). In particular, the HTTPS RR (RR type 65) provides
provides special handling for the case of "https" origins as special handling for the case of "https" origins as described in
described in Section 9. Section 9.
SVCB RRs are extensible by a list of SvcParams, which are pairs SVCB RRs are extensible by a list of SvcParams, which are pairs
consisting of a SvcParamKey and a SvcParamValue. Each SvcParamKey consisting of a SvcParamKey and a SvcParamValue. Each SvcParamKey
has a presentation name and a registered number. Values are in a has a presentation name and a registered number. Values are in a
format specific to the SvcParamKey. Each SvcParam has a specified format specific to the SvcParamKey. Each SvcParam has a specified
presentation format (used in zone files) and wire encoding (e.g., presentation format (used in zone files) and wire encoding (e.g.,
domain names, binary data, or numeric values). The initial domain names, binary data, or numeric values). The initial
SvcParamKeys and their formats are defined in Section 7. SvcParamKeys and their formats are defined in Section 7.
2.1. Zone file presentation format 2.1. Zone-File Presentation Format
The presentation format <RDATA> of the record ([RFC1035], The presentation format <RDATA> of the record ([RFC1035],
Section 5.1) has the form: Section 5.1) has the form:
SvcPriority TargetName SvcParams SvcPriority TargetName SvcParams
The SVCB record is defined specifically within the Internet ("IN") The SVCB record is defined specifically within the Internet ("IN")
Class ([RFC1035], Section 3.2.4). Class ([RFC1035], Section 3.2.4).
SvcPriority is a number in the range 0-65535, TargetName is a SvcPriority is a number in the range 0-65535, TargetName is a
<domain-name> ([RFC1035], Section 5.1), and the SvcParams are a <domain-name> ([RFC1035], Section 5.1), and the SvcParams are a
whitespace-separated list, with each SvcParam consisting of a whitespace-separated list with each SvcParam consisting of a
SvcParamKey=SvcParamValue pair or a standalone SvcParamKey. SvcParamKey=SvcParamValue pair or a standalone SvcParamKey.
SvcParamKeys are subject to IANA control (Section 14.3). SvcParamKeys are registered by IANA (Section 14.3).
Each SvcParamKey SHALL appear at most once in the SvcParams. In Each SvcParamKey SHALL appear at most once in the SvcParams. In
presentation format, SvcParamKeys are lower-case alphanumeric presentation format, SvcParamKeys are lowercase alphanumeric strings.
strings. Key names contain 1-63 characters from the ranges "a"-"z", Key names contain 1-63 characters from the ranges "a"-"z", "0"-"9",
"0"-"9", and "-". In ABNF [RFC5234], and "-". In ABNF [RFC5234],
alpha-lc = %x61-7A ; a-z alpha-lc = %x61-7A ; a-z
SvcParamKey = 1*63(alpha-lc / DIGIT / "-") SvcParamKey = 1*63(alpha-lc / DIGIT / "-")
SvcParam = SvcParamKey ["=" SvcParamValue] SvcParam = SvcParamKey ["=" SvcParamValue]
SvcParamValue = char-string ; See Appendix A SvcParamValue = char-string ; See Appendix A.
value = *OCTET ; Value before key-specific parsing value = *OCTET ; Value before key-specific parsing
The SvcParamValue is parsed using the character-string decoding The SvcParamValue is parsed using the character-string decoding
algorithm (Appendix A), producing a value. The value is then algorithm (Appendix A), producing a value. The value is then
validated and converted into wire-format in a manner specific to each validated and converted into wire format in a manner specific to each
key. key.
When the optional "=" and SvcParamValue are omitted, the value is When the optional "=" and SvcParamValue are omitted, the value is
interpreted as empty. interpreted as empty.
Arbitrary keys can be represented using the unknown-key presentation Arbitrary keys can be represented using the unknown-key presentation
format "keyNNNNN" where NNNNN is the numeric value of the key type format "keyNNNNN" where NNNNN is the numeric value of the key type
without leading zeros. A SvcParam in this form SHALL be parsed as without leading zeros. A SvcParam in this form SHALL be parsed as
specified above, and the decoded value SHALL be used as its wire specified above, and the decoded value SHALL be used as its wire-
format encoding. format encoding.
For some SvcParamKeys, the value corresponds to a list or set of For some SvcParamKeys, the value corresponds to a list or set of
items. Presentation formats for such keys SHOULD use a comma- items. Presentation formats for such keys SHOULD use a comma-
separated list (Appendix A.1). separated list (Appendix A.1).
SvcParams in presentation format MAY appear in any order, but keys SvcParams in presentation format MAY appear in any order, but keys
MUST NOT be repeated. MUST NOT be repeated.
2.2. RDATA wire format 2.2. RDATA Wire Format
The RDATA for the SVCB RR consists of: The RDATA for the SVCB RR consists of:
* a 2-octet field for SvcPriority as an integer in network byte * a 2-octet field for SvcPriority as an integer in network byte
order. order.
* the uncompressed, fully-qualified TargetName, represented as a * the uncompressed, fully qualified TargetName, represented as a
sequence of length-prefixed labels as in Section 3.1 of [RFC1035]. sequence of length-prefixed labels per Section 3.1 of [RFC1035].
* the SvcParams, consuming the remainder of the record (so smaller * the SvcParams, consuming the remainder of the record (so smaller
than 65535 octets and constrained by the RDATA and DNS message than 65535 octets and constrained by the RDATA and DNS message
sizes). sizes).
When the list of SvcParams is non-empty, it contains a series of When the list of SvcParams is non-empty, it contains a series of
SvcParamKey=SvcParamValue pairs, represented as: SvcParamKey=SvcParamValue pairs, represented as:
* a 2-octet field containing the SvcParamKey as an integer in * a 2-octet field containing the SvcParamKey as an integer in
network byte order. (See Section 14.3.2 for the defined values.) network byte order. (See Section 14.3.2 for the defined values.)
skipping to change at page 9, line 39 skipping to change at line 408
SvcParamValue in a format determined by the SvcParamKey. SvcParamValue in a format determined by the SvcParamKey.
SvcParamKeys SHALL appear in increasing numeric order. SvcParamKeys SHALL appear in increasing numeric order.
Clients MUST consider an RR malformed if: Clients MUST consider an RR malformed if:
* the end of the RDATA occurs within a SvcParam. * the end of the RDATA occurs within a SvcParam.
* SvcParamKeys are not in strictly increasing numeric order. * SvcParamKeys are not in strictly increasing numeric order.
* the SvcParamValue for an SvcParamKey does not have the expected * the SvcParamValue for a SvcParamKey does not have the expected
format. format.
Note that the second condition implies that there are no duplicate Note that the second condition implies that there are no duplicate
SvcParamKeys. SvcParamKeys.
If any RRs are malformed, the client MUST reject the entire RRSet and If any RRs are malformed, the client MUST reject the entire RRset and
fall back to non-SVCB connection establishment. fall back to non-SVCB connection establishment.
2.3. SVCB query names 2.3. SVCB Query Names
When querying the SVCB RR, a service is translated into a QNAME by When querying the SVCB RR, a service is translated into a QNAME by
prepending the service name with a label indicating the scheme, prepending the service name with a label indicating the scheme,
prefixed with an underscore, resulting in a domain name like prefixed with an underscore, resulting in a domain name like
"_examplescheme.api.example.com.". This follows the Attrleaf naming "_examplescheme.api.example.com.". This follows the Attrleaf naming
pattern [Attrleaf], so the scheme MUST be registered appropriately pattern [Attrleaf], so the scheme MUST be registered appropriately
with IANA (see Section 11). with IANA (see Section 11).
Protocol mapping documents MAY specify additional underscore-prefixed Protocol mapping documents MAY specify additional underscore-prefixed
labels to be prepended. For schemes that specify a port labels to be prepended. For schemes that specify a port
(Section 3.2.3 of [URI]), one reasonable possibility is to prepend (Section 3.2.3 of [URI]), one reasonable possibility is to prepend
the indicated port number if a non-default port number is specified. the indicated port number if a non-default port number is specified.
We term this behavior "Port Prefix Naming", and use it in the This document terms this behavior "Port Prefix Naming" and uses it in
examples throughout this document. the examples throughout.
See Section 9.1 for the HTTPS RR behavior. See Section 9.1 for information regarding HTTPS RR behavior.
When a prior CNAME or SVCB record has aliased to a SVCB record, each When a prior CNAME or SVCB record has aliased to a SVCB record, each
RR SHALL be returned under its own owner name, as in ordinary CNAME RR SHALL be returned under its own owner name, as in ordinary CNAME
processing ([RFC1034], Section 3.6.2). For details, see the processing ([RFC1034], Section 3.6.2). For details, see the
recommendations regarding aliases for clients (Section 3), servers recommendations regarding aliases for clients (Section 3), servers
(Section 4), and zones (Section 10). (Section 4), and zones (Section 10).
Note that none of these forms alter the origin or authority for Note that none of these forms alter the origin or authority for
validation purposes. For example, TLS clients MUST continue to validation purposes. For example, TLS clients MUST continue to
validate TLS certificates for the original service name. validate TLS certificates for the original service name.
As an example, the owner of example.com could publish this record: As an example, the owner of "example.com" could publish this record:
_8443._foo.api.example.com. 7200 IN SVCB 0 svc4.example.net. _8443._foo.api.example.com. 7200 IN SVCB 0 svc4.example.net.
to indicate that "foo://api.example.com:8443" is aliased to This record would indicate that "foo://api.example.com:8443" is
"svc4.example.net". The owner of example.net, in turn, could publish aliased to "svc4.example.net". The owner of "example.net", in turn,
this record: could publish this record:
svc4.example.net. 7200 IN SVCB 3 svc4.example.net. ( svc4.example.net. 7200 IN SVCB 3 svc4.example.net. (
alpn="bar" port="8004" ) alpn="bar" port="8004" )
to indicate that these services are served on port number 8004, which This record would indicate that these services are served on port
supports the protocol "bar" and its associated transport in addition number 8004, which supports the protocol "bar" and its associated
to the default transport protocol for "foo://". transport in addition to the default transport protocol for "foo://".
(Parentheses are used to ignore a line break in DNS zone file (Parentheses are used to ignore a line break in DNS zone-file
presentation format ([RFC1035], Section 5.1).) presentation format, per Section 5.1 of [RFC1035].)
2.4. Interpretation 2.4. Interpretation
2.4.1. SvcPriority 2.4.1. SvcPriority
When SvcPriority is 0 the SVCB record is in AliasMode When SvcPriority is 0, the SVCB record is in AliasMode
(Section 2.4.2). Otherwise, it is in ServiceMode (Section 2.4.3). (Section 2.4.2). Otherwise, it is in ServiceMode (Section 2.4.3).
Within a SVCB RRSet, all RRs SHOULD have the same Mode. If an RRSet Within a SVCB RRset, all RRs SHOULD have the same mode. If an RRset
contains a record in AliasMode, the recipient MUST ignore any contains a record in AliasMode, the recipient MUST ignore any
ServiceMode records in the set. ServiceMode records in the set.
RRSets are explicitly unordered collections, so the SvcPriority field RRsets are explicitly unordered collections, so the SvcPriority field
is used to impose an ordering on SVCB RRs. A smaller SvcPriority is used to impose an ordering on SVCB RRs. A smaller SvcPriority
indicates that the domain owner recommends use of this record over indicates that the domain owner recommends the use of this record
ServiceMode RRs with a larger SvcPriority value. over ServiceMode RRs with a larger SvcPriority value.
When receiving an RRSet containing multiple SVCB records with the When receiving an RRset containing multiple SVCB records with the
same SvcPriority value, clients SHOULD apply a random shuffle within same SvcPriority value, clients SHOULD apply a random shuffle within
a priority level to the records before using them, to ensure uniform a priority level to the records before using them, to ensure uniform
load-balancing. load balancing.
2.4.2. AliasMode 2.4.2. AliasMode
In AliasMode, the SVCB record aliases a service to a TargetName. In AliasMode, the SVCB record aliases a service to a TargetName.
SVCB RRSets SHOULD only have a single resource record in AliasMode. SVCB RRsets SHOULD only have a single RR in AliasMode. If multiple
If multiple are present, clients or recursive resolvers SHOULD pick AliasMode RRs are present, clients or recursive resolvers SHOULD pick
one at random. one at random.
The primary purpose of AliasMode is to allow aliasing at the zone The primary purpose of AliasMode is to allow aliasing at the zone
apex, where CNAME is not allowed (see e.g. [RFC1912], Section 2.4). apex, where CNAME is not allowed (see, for example, [RFC1912],
In AliasMode, the TargetName will be the name of a domain that Section 2.4). In AliasMode, the TargetName will be the name of a
resolves to SVCB, AAAA, and/or A records. (See Section 6 for domain that resolves to SVCB, AAAA, and/or A records. (See Section 6
aliasing of SVCB-compatible RR types.) Unlike CNAME, AliasMode for aliasing of SVCB-compatible RR types.) Unlike CNAME, AliasMode
records do not affect the resolution of other RR types, and apply records do not affect the resolution of other RR types and apply only
only to a specific service, not an entire domain name. to a specific service, not an entire domain name.
The AliasMode TargetName SHOULD NOT be equal to the owner name, as The AliasMode TargetName SHOULD NOT be equal to the owner name, as
this would result in a loop. In AliasMode, recipients MUST ignore this would result in a loop. In AliasMode, recipients MUST ignore
any SvcParams that are present. Zone-file parsers MAY emit a warning any SvcParams that are present. Zone-file parsers MAY emit a warning
if an AliasMode record has SvcParams. The use of SvcParams in if an AliasMode record has SvcParams. The use of SvcParams in
AliasMode records is currently not defined, but a future AliasMode records is currently not defined, but a future
specification could extend AliasMode records to include SvcParams. specification could extend AliasMode records to include SvcParams.
For example, the operator of foo://example.com:8080 could point For example, the operator of "foo://example.com:8080" could point
requests to a service operating at foosvc.example.net by publishing: requests to a service operating at "foosvc.example.net" by
publishing:
_8080._foo.example.com. 3600 IN SVCB 0 foosvc.example.net. _8080._foo.example.com. 3600 IN SVCB 0 foosvc.example.net.
Using AliasMode maintains a separation of concerns: the owner of Using AliasMode maintains a separation of concerns: the owner of
foosvc.example.net can add or remove ServiceMode SVCB records without "foosvc.example.net" can add or remove ServiceMode SVCB records
requiring a corresponding change to example.com. Note that if without requiring a corresponding change to "example.com". Note that
foosvc.example.net promises to always publish a SVCB record, this if "foosvc.example.net" promises to always publish a SVCB record,
AliasMode record can be replaced by a CNAME at the same owner name, this AliasMode record can be replaced by a CNAME at the same owner
which would likely improve performance. name.
AliasMode is especially useful for SVCB-compatible RR types that do AliasMode is especially useful for SVCB-compatible RR types that do
not require an underscore prefix, such as the HTTPS RR type. For not require an underscore prefix, such as the HTTPS RR type. For
example, the operator of https://example.com could point requests to example, the operator of "https://example.com" could point requests
a server at svc.example.net by publishing this record at the zone to a server at "svc.example.net" by publishing this record at the
apex: zone apex:
example.com. 3600 IN HTTPS 0 svc.example.net. example.com. 3600 IN HTTPS 0 svc.example.net.
Note that the SVCB record's owner name MAY be the canonical name of a Note that the SVCB record's owner name MAY be the canonical name of a
CNAME record, and the TargetName MAY be the owner of a CNAME record. CNAME record, and the TargetName MAY be the owner of a CNAME record.
Clients and recursive resolvers MUST follow CNAMEs as normal. Clients and recursive resolvers MUST follow CNAMEs as normal.
To avoid unbounded alias chains, clients and recursive resolvers MUST To avoid unbounded alias chains, clients and recursive resolvers MUST
impose a limit on the total number of SVCB aliases they will follow impose a limit on the total number of SVCB aliases they will follow
for each resolution request. This limit MUST NOT be zero, i.e. for each resolution request. This limit MUST NOT be zero, i.e.,
implementations MUST be able to follow at least one AliasMode record. implementations MUST be able to follow at least one AliasMode record.
The exact value of this limit is left to implementations. The exact value of this limit is left to implementations.
Zones that require following multiple AliasMode records could Zones that require following multiple AliasMode records could
encounter compatibility and performance issues. encounter compatibility and performance issues.
As legacy clients will not know to use this record, service operators As legacy clients will not know to use this record, service operators
will likely need to retain fallback AAAA and A records alongside this will likely need to retain fallback AAAA and A records alongside this
SVCB record, although in a common case the target of the SVCB record SVCB record, although in a common case the target of the SVCB record
might offer better performance, and therefore would be preferable for might offer better performance, and therefore would be preferable for
clients implementing this specification to use. clients implementing this specification to use.
AliasMode records only apply to queries for the specific RR type. AliasMode records only apply to queries for the specific RR type.
For example, a SVCB record cannot alias to an HTTPS record, nor vice- For example, a SVCB record cannot alias to an HTTPS record or vice
versa. versa.
2.4.3. ServiceMode 2.4.3. ServiceMode
In ServiceMode, the TargetName and SvcParams within each resource In ServiceMode, the TargetName and SvcParams within each RR associate
record associate an alternative endpoint for the service with its an alternative endpoint for the service with its connection
connection parameters. parameters.
Each protocol scheme that uses SVCB MUST define a protocol mapping Each protocol scheme that uses SVCB MUST define a protocol mapping
that explains how SvcParams are applied for connections of that that explains how SvcParams are applied for connections of that
scheme. Unless specified otherwise by the protocol mapping, clients scheme. Unless specified otherwise by the protocol mapping, clients
MUST ignore any SvcParam that they do not recognize. MUST ignore any SvcParam that they do not recognize.
Some SvcParams impose requirements on other SvcParams in the RR. A Some SvcParams impose requirements on other SvcParams in the RR. A
ServiceMode RR is called "self-consistent" if its SvcParams all ServiceMode RR is called "self-consistent" if its SvcParams all
comply with each other's requirements. Clients MUST reject any RR comply with each other's requirements. Clients MUST reject any RR
whose recognized SvcParams are not self-consistent, and MAY reject whose recognized SvcParams are not self-consistent and MAY reject the
the entire RRSet. To help zone operators avoid this condition, zone- entire RRset. To help zone operators avoid this condition, zone-file
file implementations SHOULD enforce self-consistency as well. implementations SHOULD enforce self-consistency as well.
2.5. Special handling of "." in TargetName 2.5. Special Handling of "." in TargetName
If TargetName has the value "." (represented in the wire format as a If TargetName has the value "." (represented in the wire format as a
zero-length label), special rules apply. zero-length label), special rules apply.
2.5.1. AliasMode 2.5.1. AliasMode
For AliasMode SVCB RRs, a TargetName of "." indicates that the For AliasMode SVCB RRs, a TargetName of "." indicates that the
service is not available or does not exist. This indication is service is not available or does not exist. This indication is
advisory: clients encountering this indication MAY ignore it and advisory: clients encountering this indication MAY ignore it and
attempt to connect without the use of SVCB. attempt to connect without the use of SVCB.
2.5.2. ServiceMode 2.5.2. ServiceMode
For ServiceMode SVCB RRs, if TargetName has the value ".", then the For ServiceMode SVCB RRs, if TargetName has the value ".", then the
owner name of this record MUST be used as the effective TargetName. owner name of this record MUST be used as the effective TargetName.
If the record has a wildcard owner name in the zone file, the If the record has a wildcard owner name in the zone file, the
recipient SHALL use the response's synthesized owner name as the recipient SHALL use the response's synthesized owner name as the
effective TargetName. effective TargetName.
For example, in the following example "svc2.example.net" is the Here, for example, "svc2.example.net" is the effective TargetName:
effective TargetName:
example.com. 7200 IN HTTPS 0 svc.example.net. example.com. 7200 IN HTTPS 0 svc.example.net.
svc.example.net. 7200 IN CNAME svc2.example.net. svc.example.net. 7200 IN CNAME svc2.example.net.
svc2.example.net. 7200 IN HTTPS 1 . port=8002 svc2.example.net. 7200 IN HTTPS 1 . port=8002
svc2.example.net. 300 IN A 192.0.2.2 svc2.example.net. 300 IN A 192.0.2.2
svc2.example.net. 300 IN AAAA 2001:db8::2 svc2.example.net. 300 IN AAAA 2001:db8::2
3. Client behavior 3. Client Behavior
"SVCB resolution" is the process of enumerating the priority-ordered "SVCB resolution" is the process of enumerating and ordering the
endpoints for a service, as performed by the client. SVCB resolution available endpoints for a service, as performed by the client. SVCB
is implemented as follows: resolution is implemented as follows:
1. Let $QNAME be the service name plus appropriate prefixes for the 1. Let $QNAME be the service name plus appropriate prefixes for the
scheme (see Section 2.3). scheme (see Section 2.3).
2. Issue a SVCB query for $QNAME. 2. Issue a SVCB query for $QNAME.
3. If an AliasMode SVCB record is returned for $QNAME (after 3. If an AliasMode SVCB record is returned for $QNAME (after
following CNAMEs as normal), set $QNAME to its TargetName following CNAMEs as normal), set $QNAME to its TargetName
(without additional prefixes) and loop back to step 2, subject to (without additional prefixes) and loop back to Step 2, subject to
chain length limits and loop detection heuristics (see chain length limits and loop detection heuristics (see
Section 3.1). Section 3.1).
4. If one or more "compatible" (Section 8) ServiceMode records are 4. If one or more "compatible" (Section 8) ServiceMode records are
returned, these represent the alternative endpoints. returned, these represent the alternative endpoints. Sort the
records by ascending SvcPriority.
5. Otherwise, SVCB resolution has failed, and the list of known 5. Otherwise, SVCB resolution has failed, and the list of available
endpoints is empty. endpoints is empty.
This procedure does not rely on any recursive or authoritative DNS This procedure does not rely on any recursive or authoritative DNS
server to comply with this specification or have any awareness of server to comply with this specification or have any awareness of
SVCB. SVCB.
A client is called "SVCB-optional" if it can connect without the use A client is called "SVCB-optional" if it can connect without the use
of ServiceMode records, and "SVCB-reliant" otherwise. Clients for of ServiceMode records; otherwise, it is called "SVCB-reliant".
pre-existing protocols (e.g. HTTP) SHALL implement SVCB-optional Clients for pre-existing protocols (e.g., HTTP) SHALL implement SVCB-
behavior (except as noted in Section 3.1 or when modified by future optional behavior (except as noted in Section 3.1 or when modified by
specifications). future specifications).
SVCB-optional clients SHOULD issue in parallel any other DNS queries SVCB-optional clients SHOULD issue in parallel any other DNS queries
that might be needed for connection establishment if the SVCB record that might be needed for connection establishment if the SVCB record
is absent, in order to minimize delay in that case and enable the is absent, in order to minimize delay in that case and enable the
optimizations discussed in Section 5. optimizations discussed in Section 5.
Once SVCB resolution has concluded, whether successful or not, if at Once SVCB resolution has concluded, whether successful or not, if at
least one AliasMode record was processed, SVCB-optional clients SHALL least one AliasMode record was processed, SVCB-optional clients SHALL
append to the priority list an endpoint consisting of the final value append to the list of endpoints an endpoint consisting of the final
of $QNAME, the authority endpoint's port number, and no SvcParams. value of $QNAME, the authority endpoint's port number, and no
(This endpoint will be attempted before falling back to non-SVCB SvcParams. (This endpoint will be attempted before falling back to
connection modes. This ensures that SVCB-optional clients will make non-SVCB connection modes. This ensures that SVCB-optional clients
use of an AliasMode record whose TargetName has A and/or AAAA records will make use of an AliasMode record whose TargetName has A and/or
but no SVCB records.) AAAA records but no SVCB records.)
The client proceeds with connection establishment using the resolved The client proceeds with connection establishment using this list of
list of endpoints. Clients SHOULD try higher-priority alternatives endpoints. Clients SHOULD try higher-priority alternatives first,
first, with fallback to lower-priority alternatives. Clients resolve with fallback to lower-priority alternatives. Clients resolve AAAA
AAAA and/or A records for the selected TargetName, and MAY choose and/or A records for the selected TargetName and MAY choose between
between them using an approach such as Happy Eyeballs them using an approach such as Happy Eyeballs [HappyEyeballsV2].
[HappyEyeballsV2].
If the client is SVCB-optional, and connecting using this list of If the client is SVCB-optional and connecting using this list of
endpoints has failed, the client now attempts to use non-SVCB endpoints has failed, the client now attempts to use non-SVCB
connection modes. connection modes.
Some important optimizations are discussed in Section 5 to avoid Some important optimizations are discussed in Section 5 to avoid
additional latency in comparison to ordinary AAAA/A lookups. additional latency in comparison to ordinary AAAA/A lookups.
3.1. Handling resolution failures 3.1. Handling Resolution Failures
If DNS responses are cryptographically protected (e.g. using DNSSEC If DNS responses are cryptographically protected (e.g., using DNSSEC
or TLS [DoT][DoH]), and SVCB resolution fails due to an or TLS [DoT] [DoH]) and SVCB resolution fails due to an
authentication error, SERVFAIL response, transport error, or timeout, authentication error, SERVFAIL response, transport error, or timeout,
the client SHOULD abandon its attempt to reach the service, even if the client SHOULD abandon its attempt to reach the service, even if
the client is SVCB-optional. Otherwise, an active attacker could the client is SVCB-optional. Otherwise, an active attacker could
mount a downgrade attack by denying the user access to the SvcParams. mount a downgrade attack by denying the user access to the SvcParams.
A SERVFAIL error can occur if the domain is DNSSEC-signed, the A SERVFAIL error can occur if the domain is DNSSEC-signed, the
recursive resolver is DNSSEC-validating, and the attacker is between recursive resolver is DNSSEC-validating, and the attacker is between
the recursive resolver and the authoritative DNS server. A transport the recursive resolver and the authoritative DNS server. A transport
error or timeout can occur if an active attacker between the client error or timeout can occur if an active attacker between the client
and the recursive resolver is selectively dropping SVCB queries or and the recursive resolver is selectively dropping SVCB queries or
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If the client enforces DNSSEC validation on A/AAAA responses, it If the client enforces DNSSEC validation on A/AAAA responses, it
SHOULD apply the same validation policy to SVCB. Otherwise, an SHOULD apply the same validation policy to SVCB. Otherwise, an
attacker could defeat the A/AAAA protection by forging SVCB responses attacker could defeat the A/AAAA protection by forging SVCB responses
that direct the client to other IP addresses. that direct the client to other IP addresses.
If DNS responses are not cryptographically protected, clients MAY If DNS responses are not cryptographically protected, clients MAY
treat SVCB resolution failure as fatal or nonfatal. treat SVCB resolution failure as fatal or nonfatal.
If the client is unable to complete SVCB resolution due to its chain If the client is unable to complete SVCB resolution due to its chain
length limit, the client MUST fall back to the authority endpoint, as length limit, the client MUST fall back to the authority endpoint, as
if the origin's SVCB record did not exist. if the service's SVCB record did not exist.
3.2. Clients using a Proxy 3.2. Clients Using a Proxy
Clients using a domain-oriented transport proxy like HTTP CONNECT Clients using a domain-oriented transport proxy like HTTP CONNECT
([RFC7231], Section 4.3.6) or SOCKS5 ([RFC1928]) have the option to ([RFC7231], Section 4.3.6) or SOCKS5 [RFC1928] have the option of
use named destinations, in which case the client does not perform any using named destinations, in which case the client does not perform
A or AAAA queries for destination domains. If the client is any A or AAAA queries for destination domains. If the client is
configured to use named destinations with a proxy that does not configured to use named destinations with a proxy that does not
provide SVCB query capability (e.g. through an affiliated DNS provide SVCB query capability (e.g., through an affiliated DNS
resolver), the client would have to perform SVCB resolution resolver), the client would have to perform SVCB resolution
separately, likely disclosing the destinations to additional parties separately, likely disclosing the destinations to additional parties
than just the proxy. Clients in this configuration SHOULD arrange and not just the proxy. Clients in this configuration SHOULD arrange
for a separate SVCB resolution procedure with appropriate privacy for a separate SVCB resolution procedure with appropriate privacy
properties. If this is not possible, SVCB-optional clients MUST properties. If this is not possible, SVCB-optional clients MUST
disable SVCB resolution entirely, and SVCB-reliant clients MUST treat disable SVCB resolution entirely, and SVCB-reliant clients MUST treat
the configuration as invalid. the configuration as invalid.
If the client does use SVCB and named destinations, the client SHOULD If the client does use SVCB and named destinations, the client SHOULD
follow the standard SVCB resolution process, selecting the smallest- follow the standard SVCB resolution process, selecting the smallest-
SvcPriority option that is compatible with the client and the proxy. SvcPriority option that is compatible with the client and the proxy.
When connecting using a SVCB record, clients MUST provide the final When connecting using a SVCB record, clients MUST provide the final
TargetName and port to the proxy, which will perform any required A TargetName and port to the proxy, which will perform any required A
and AAAA lookups. and AAAA lookups.
This arrangement has several benefits: This arrangement has several benefits:
* Compared to disabling SVCB: * Compared to disabling SVCB:
- It allows the client to use the SvcParams, if present, which - It allows the client to use the SvcParams, if present, which
are only usable with a specific TargetName. The SvcParams may are only usable with a specific TargetName. The SvcParams may
include information that enhances performance (e.g. alpn) and include information that enhances performance (e.g., supported
privacy. protocols) and privacy.
- It allows the service to delegate the apex domain. - It allows a service on an apex domain to use aliasing.
* Compared to providing the proxy with an IP address: * Compared to providing the proxy with an IP address:
- It allows the proxy to select between IPv4 and IPv6 addresses - It allows the proxy to select between IPv4 and IPv6 addresses
for the server according to its configuration. for the server according to its configuration.
- It ensures that the proxy receives addresses based on its - It ensures that the proxy receives addresses based on its
network geolocation, not the client's. network geolocation, not the client's.
- It enables faster fallback for TCP destinations with multiple - It enables faster fallback for TCP destinations with multiple
addresses of the same family. addresses of the same family.
4. DNS Server Behavior 4. DNS Server Behavior
4.1. Authoritative servers 4.1. Authoritative Servers
When replying to a SVCB query, authoritative DNS servers SHOULD When replying to a SVCB query, authoritative DNS servers SHOULD
return A, AAAA, and SVCB records in the Additional Section for any return A, AAAA, and SVCB records in the Additional section for any
TargetNames that are in the zone. If the zone is signed, the server TargetNames that are in the zone. If the zone is signed, the server
SHOULD also include positive or negative DNSSEC responses for these SHOULD also include DNSSEC records authenticating the existence or
records in the Additional section. nonexistence of these records in the Additional section.
See Section 4.4 for exceptions. See Section 4.4 for exceptions.
4.2. Recursive resolvers 4.2. Recursive Resolvers
Whether the recursive resolver is aware of SVCB or not, the normal Whether the recursive resolver is aware of SVCB or not, the normal
response construction process (i.e. unknown RR type resolution under response construction process used for unknown RR types [RFC3597]
[RFC3597]) generates the Answer section of the response. Recursive generates the Answer section of the response. Recursive resolvers
resolvers that are aware of SVCB SHOULD help the client to execute that are aware of SVCB SHOULD help the client to execute the
the procedure in Section 3 with minimum overall latency by procedure in Section 3 with minimum overall latency by incorporating
incorporating additional useful information into the Additional additional useful information into the Additional section of the
section of the response as follows: response as follows:
1. Incorporate the results of SVCB resolution. If the recursive 1. Incorporate the results of SVCB resolution. If the recursive
resolver's local chain length limit (which may be different from resolver's local chain length limit (which may be different from
the client's limit) has been reached, terminate. the client's limit) has been reached, terminate.
2. If any of the resolved SVCB records are in AliasMode, choose one 2. If any of the resolved SVCB records are in AliasMode, choose one
of them at random, and resolve SVCB, A, and AAAA records for its of them at random, and resolve SVCB, A, and AAAA records for its
TargetName. TargetName.
* If any SVCB records are resolved, go to step 1. * If any SVCB records are resolved, go to Step 1.
* Otherwise, incorporate the results of A and AAAA resolution, * Otherwise, incorporate the results of A and AAAA resolution,
and terminate. and terminate.
3. All the resolved SVCB records are in ServiceMode. Resolve A and 3. All the resolved SVCB records are in ServiceMode. Resolve A and
AAAA queries for each TargetName (or for the owner name if AAAA queries for each TargetName (or for the owner name if
TargetName is "."), incorporate all the results, and terminate. TargetName is "."), incorporate all the results, and terminate.
In this procedure, "resolve" means the resolver's ordinary recursive In this procedure, "resolve" means the resolver's ordinary recursive
resolution procedure, as if processing a query for that RRSet. This resolution procedure, as if processing a query for that RRset. This
includes following any aliases that the resolver would ordinarily includes following any aliases that the resolver would ordinarily
follow (e.g. CNAME, DNAME [DNAME]). Errors or anomalies in follow (e.g., CNAME, DNAME [DNAME]). Errors or anomalies in
obtaining additional records MAY cause this process to terminate, but obtaining additional records MAY cause this process to terminate but
MUST NOT themselves cause the resolver to send a failure response. MUST NOT themselves cause the resolver to send a failure response.
See Section 2.4.2 for additional safeguards for recursive resolvers See Section 2.4.2 for additional safeguards for recursive resolvers
to implement to mitigate loops. to implement to mitigate loops.
See Section 5.2 for possible optimizations of this procedure. See Section 5.2 for possible optimizations of this procedure.
4.2.1. DNS64 4.2.1. DNS64
DNS64 resolvers synthesize responses to AAAA queries for names that DNS64 resolvers synthesize responses to AAAA queries for names that
only have an A record (Section 5.1.7 of [RFC6147]). SVCB-aware DNS64 only have an A record (Section 5.1.7 of [RFC6147]). SVCB-aware DNS64
resolvers SHOULD apply the same synthesis logic when resolving AAAA resolvers SHOULD apply the same synthesis logic when resolving AAAA
records for the TargetName for inclusion as Additionals (Step 2 in records for the TargetName for inclusion in the Additional section
Section 4.2), and MAY omit the Additional A records. (Step 2 in Section 4.2) and MAY omit the A records from this section.
DNS64 resolvers MUST NOT extrapolate the AAAA synthesis logic to the DNS64 resolvers MUST NOT extrapolate the AAAA synthesis logic to the
IP hints in the SvcParams (Section 7.3). Modifying the IP hints IP hints in the SvcParams (Section 7.3). Modifying the IP hints
would break DNSSEC validation for the SVCB record and would not would break DNSSEC validation for the SVCB record and would not
improve performance when the above recommendation is implemented. improve performance when the above recommendation is implemented.
4.3. General requirements 4.3. General Requirements
Recursive resolvers MUST be able to convey SVCB records with Recursive resolvers MUST be able to convey SVCB records with
unrecognized SvcParamKeys, and MAY treat the entire SvcParams portion unrecognized SvcParamKeys. Resolvers MAY accomplish this by treating
of the record as opaque, even if the contents are invalid. the entire SvcParams portion of the record as opaque, even if the
Alternatively, recursive resolvers MAY report an error such as contents are invalid. If a recognized SvcParamKey is followed by a
SERVFAIL to avoid returning a SvcParamValue that is invalid according value that is invalid according to the SvcParam's specification, a
to the SvcParam's specification. For complex value types whose recursive resolver MAY report an error such as SERVFAIL instead of
interpretation might differ between implementations or have returning the record. For complex value types whose interpretation
additional future allowed values added (e.g. URIs or "alpn"), might differ between implementations or have additional future
resolvers SHOULD limit validation to specified constraints. allowed values added (e.g., URIs or "alpn"), resolvers SHOULD limit
validation to specified constraints.
When responding to a query that includes the DNSSEC OK bit When responding to a query that includes the DNSSEC OK bit [RFC3225],
([RFC3225]), DNSSEC-capable recursive and authoritative DNS servers DNSSEC-capable recursive and authoritative DNS servers MUST accompany
MUST accompany each RRSet in the Additional section with the same each RRset in the Additional section with the same DNSSEC-related
DNSSEC-related records that they would send when providing that RRSet records that they would send when providing that RRset as an Answer
as an Answer (e.g. RRSIG, NSEC, NSEC3). (e.g., RRSIG, NSEC, NSEC3).
According to Section 5.4.1 of [RFC2181], "Unauthenticated RRs According to Section 5.4.1 of [RFC2181], "Unauthenticated RRs
received and cached from ... the additional data section ... should received and cached from ... the additional data section ... should
not be cached in such a way that they would ever be returned as not be cached in such a way that they would ever be returned as
answers to a received query. They may be returned as additional answers to a received query. They may be returned as additional
information where appropriate.". Recursive resolvers therefore MAY information where appropriate." Recursive resolvers therefore MAY
cache records from the Additional section for use in populating cache records from the Additional section for use in populating
Additional section responses, and MAY cache them for general use if Additional section responses and MAY cache them for general use if
they are authenticated by DNSSEC. they are authenticated by DNSSEC.
4.4. EDNS Client Subnet (ECS) 4.4. EDNS Client Subnet (ECS)
The EDNS Client Subnet option (ECS, [RFC7871]) allows recursive The EDNS Client Subnet (ECS) option [RFC7871] allows recursive
resolvers to request IP addresses that are suitable for a particular resolvers to request IP addresses that are suitable for a particular
client IP range. SVCB records may contain IP addresses (in ipv*hint client IP range. SVCB records may contain IP addresses (in ipv*hint
SvcParams), or direct users to a subnet-specific TargetName, so SvcParams) or direct users to a subnet-specific TargetName, so
recursive resolvers SHOULD include the same ECS option in SVCB recursive resolvers SHOULD include the same ECS option in SVCB
queries as in A/AAAA queries. queries as in A/AAAA queries.
According to Section 7.3.1 of [RFC7871], "Any records from [the According to Section 7.3.1 of [RFC7871], "Any records from [the
Additional section] MUST NOT be tied to a network". Accordingly, Additional section] MUST NOT be tied to a network." Accordingly,
when processing a response whose QTYPE is SVCB-compatible, resolvers when processing a response whose QTYPE is SVCB-compatible, resolvers
SHOULD treat any records in the Additional section as having SOURCE SHOULD treat any records in the Additional section as having SOURCE
PREFIX-LENGTH zero and SCOPE PREFIX-LENGTH as specified in the ECS PREFIX-LENGTH set to zero and SCOPE PREFIX-LENGTH as specified in the
option. Authoritative servers MUST omit such records if they are not ECS option. Authoritative servers MUST omit such records if they are
suitable for use by any stub resolvers that set SOURCE PREFIX-LENGTH not suitable for use by any stub resolvers that set SOURCE PREFIX-
to zero. This will cause the resolver to perform a follow-up query LENGTH to zero. This will cause the resolver to perform a follow-up
that can receive properly tailored ECS. (This is similar to the query that can receive a properly tailored ECS. (This is similar to
usage of CNAME with ECS discussed in [RFC7871], Section 7.2.1.) the usage of CNAME with the ECS option as discussed in [RFC7871],
Section 7.2.1.)
Authoritative servers that omit Additional records can avoid the Authoritative servers that omit Additional records can avoid the
added latency of a follow-up query by following the advice in added latency of a follow-up query by following the advice in
Section 10.2. Section 10.2.
5. Performance optimizations 5. Performance Optimizations
For optimal performance (i.e. minimum connection setup time), clients For optimal performance (i.e., minimum connection setup time),
SHOULD implement a client-side DNS cache. Responses in the clients SHOULD implement a client-side DNS cache. Responses in the
Additional section of a SVCB response SHOULD be placed in cache Additional section of a SVCB response SHOULD be placed in cache
before performing any follow-up queries. With this behavior, and before performing any follow-up queries. With this behavior, and
conforming DNS servers, using SVCB does not add network latency to with conforming DNS servers, using SVCB does not add network latency
connection setup. to connection setup.
To improve performance when using a non-conforming recursive To improve performance when using a non-conforming recursive
resolver, clients SHOULD issue speculative A and/or AAAA queries in resolver, clients SHOULD issue speculative A and/or AAAA queries in
parallel with each SVCB query, based on a predicted value of parallel with each SVCB query, based on a predicted value of
TargetName (see Section 10.2). TargetName (see Section 10.2).
After a ServiceMode RRSet is received, clients MAY try more than one After a ServiceMode RRset is received, clients MAY try more than one
option in parallel, and MAY prefetch A and AAAA records for multiple option in parallel and MAY prefetch A and AAAA records for multiple
TargetNames. TargetNames.
5.1. Optimistic pre-connection and connection reuse 5.1. Optimistic Pre-connection and Connection Reuse
If an address response arrives before the corresponding SVCB If an address response arrives before the corresponding SVCB
response, the client MAY initiate a connection as if the SVCB query response, the client MAY initiate a connection as if the SVCB query
returned NODATA, but MUST NOT transmit any information that could be returned NODATA but MUST NOT transmit any information that could be
altered by the SVCB response until it arrives. For example, future altered by the SVCB response until it arrives. For example, future
SvcParamKeys could be defined that alter the TLS ClientHello. SvcParamKeys could be defined that alter the TLS ClientHello.
Clients implementing this optimization SHOULD wait for 50 Clients implementing this optimization SHOULD wait for 50
milliseconds before starting optimistic pre-connection, as per the milliseconds before starting optimistic pre-connection, as per the
guidance in [HappyEyeballsV2]. guidance in [HappyEyeballsV2].
A SVCB record is consistent with a connection if the client would A SVCB record is consistent with a connection if the client would
attempt an equivalent connection when making use of that record. If attempt an equivalent connection when making use of that record. If
a SVCB record is consistent with an active or in-progress connection a SVCB record is consistent with an active or in-progress connection
C, the client MAY prefer that record and use C as its connection. C, the client MAY prefer that record and use C as its connection.
For example, suppose the client receives this SVCB RRSet for a For example, suppose the client receives this SVCB RRset for a
protocol that uses TLS over TCP: protocol that uses TLS over TCP:
_1234._bar.example.com. 300 IN SVCB 1 svc1.example.net. ( _1234._bar.example.com. 300 IN SVCB 1 svc1.example.net. (
ipv6hint=2001:db8::1 port=1234 ) ipv6hint=2001:db8::1 port=1234 )
SVCB 2 svc2.example.net. ( SVCB 2 svc2.example.net. (
ipv6hint=2001:db8::2 port=1234 ) ipv6hint=2001:db8::2 port=1234 )
If the client has an in-progress TCP connection to If the client has an in-progress TCP connection to
[2001:db8::2]:1234, it MAY proceed with TLS on that connection, even [2001:db8::2]:1234, it MAY proceed with TLS on that connection, even
though the other record in the RRSet has higher priority. though the other record in the RRset has higher priority.
If none of the SVCB records are consistent with any active or in- If none of the SVCB records are consistent with any active or in-
progress connection, clients proceed with connection establishment as progress connection, clients proceed with connection establishment as
described in Section 3. described in Section 3.
5.2. Generating and using incomplete responses 5.2. Generating and Using Incomplete Responses
When following the procedure in Section 4.2, recursive resolvers MAY When following the procedure in Section 4.2, recursive resolvers MAY
terminate the procedure early and produce a reply that omits some of terminate the procedure early and produce a reply that omits some of
the associated RRSets. This is REQUIRED when the chain length limit the associated RRsets. This is REQUIRED when the chain length limit
is reached (Section 4.2 step 1), but might also be appropriate when is reached (Step 1 in Section 4.2) but might also be appropriate when
the maximum response size is reached, or when responding before fully the maximum response size is reached or when responding before fully
chasing dependencies would improve performance. When omitting chasing dependencies would improve performance. When omitting
certain RRSets, recursive resolvers SHOULD prioritize information for certain RRsets, recursive resolvers SHOULD prioritize information for
smaller-SvcPriority records. smaller-SvcPriority records.
As discussed in Section 3, clients MUST be able to fetch additional As discussed in Section 3, clients MUST be able to fetch additional
information that is required to use a SVCB record, if it is not information that is required to use a SVCB record, if it is not
included in the initial response. As a performance optimization, if included in the initial response. As a performance optimization, if
some of the SVCB records in the response can be used without some of the SVCB records in the response can be used without
requiring additional DNS queries, the client MAY prefer those requiring additional DNS queries, the client MAY prefer those
records, regardless of their priorities. records, regardless of their priorities.
6. SVCB-compatible 6. SVCB-Compatible RR Types
An RR type is called "SVCB-compatible" if it permits an An RR type is called "SVCB-compatible" if it permits an
implementation that is identical to SVCB in its: implementation that is identical to SVCB in its:
* RDATA presentation format * RDATA presentation format
* RDATA wire format * RDATA wire format
* IANA registry used for SvcParamKeys * IANA registry used for SvcParamKeys
* Authoritative server Additional Section processing * Authoritative server Additional section processing
* Recursive resolution process * Recursive resolution process
* Relevant Class (i.e. Internet ("IN") [RFC1035]) * Relevant Class (i.e., Internet ("IN") [RFC1035])
This allows authoritative and recursive DNS servers to apply This allows authoritative and recursive DNS servers to apply
identical processing to all SVCB-compatible RR types. identical processing to all SVCB-compatible RR types.
All other behaviors described as applying to the SVCB RR also apply All other behaviors described as applying to the SVCB RR also apply
to all SVCB-compatible RR types unless explicitly stated otherwise. to all SVCB-compatible RR types unless explicitly stated otherwise.
When following an AliasMode record (Section 2.4.2) of RR type $T , When following an AliasMode record (Section 2.4.2) of RR type $T, the
the followup query to the TargetName MUST also be for type $T. follow-up query to the TargetName MUST also be for type $T.
This document defines one SVCB-compatible RR type (other than SVCB This document defines one SVCB-compatible RR type (other than SVCB
itself): the HTTPS RR type (Section 9), which avoids Attrleaf label itself): the HTTPS RR type (Section 9), which avoids Attrleaf label
prefixes [Attrleaf] in order to improve compatibility with wildcards prefixes [Attrleaf] in order to improve compatibility with wildcards
and CNAMEs, which are widely used with HTTP. and CNAMEs, which are widely used with HTTP.
Standards authors should consider carefully whether to use SVCB or Standards authors should consider carefully whether to use SVCB or
define a new SVCB-compatible RR type, as this choice cannot easily be define a new SVCB-compatible RR type, as this choice cannot easily be
reversed after deployment. reversed after deployment.
skipping to change at page 21, line 35 skipping to change at line 963
applicable to other schemes as well. applicable to other schemes as well.
Each new protocol mapping document MUST specify which keys are Each new protocol mapping document MUST specify which keys are
applicable and safe to use. Protocol mappings MAY alter the applicable and safe to use. Protocol mappings MAY alter the
interpretation of SvcParamKeys but MUST NOT alter their presentation interpretation of SvcParamKeys but MUST NOT alter their presentation
or wire formats. or wire formats.
7.1. "alpn" and "no-default-alpn" 7.1. "alpn" and "no-default-alpn"
The "alpn" and "no-default-alpn" SvcParamKeys together indicate the The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
set of Application Layer Protocol Negotiation (ALPN) protocol set of Application-Layer Protocol Negotiation (ALPN) protocol
identifiers [ALPN] and associated transport protocols supported by identifiers [ALPN] and associated transport protocols supported by
this service endpoint (the "SVCB ALPN set"). this service endpoint (the "SVCB ALPN set").
As with Alt-Svc [AltSvc], each ALPN protocol identifier is used to As with Alt-Svc [AltSvc], each ALPN protocol identifier is used to
identify the application protocol and associated suite of protocols identify the application protocol and associated suite of protocols
supported by the endpoint (the "protocol suite"). The presence of an supported by the endpoint (the "protocol suite"). The presence of an
ALPN protocol identifier in the SVCB ALPN set indicates that this ALPN protocol identifier in the SVCB ALPN set indicates that this
service endpoint, described by TargetName and the other parameters service endpoint, described by TargetName and the other parameters
(e.g. "port") offers service with the protocol suite associated with (e.g., "port"), offers service with the protocol suite associated
this ALPN identifier. with this ALPN identifier.
Clients filter the set of ALPN identifiers to match the protocol Clients filter the set of ALPN identifiers to match the protocol
suites they support, and this informs the underlying transport suites they support, and this informs the underlying transport
protocol used (such as QUIC-over-UDP or TLS-over-TCP). ALPN protocol protocol used (such as QUIC over UDP or TLS over TCP). ALPN protocol
identifiers that do not uniquely identify a protocol suite (e.g. an identifiers that do not uniquely identify a protocol suite (e.g., an
Identification Sequence that can be used with both TLS and DTLS) are Identification Sequence that can be used with both TLS and DTLS) are
not compatible with this SvcParamKey and MUST NOT be included in the not compatible with this SvcParamKey and MUST NOT be included in the
SVCB ALPN set. SVCB ALPN set.
7.1.1. Representation 7.1.1. Representation
ALPNs are identified by their registered "Identification Sequence" ALPNs are identified by their registered "Identification Sequence"
(alpn-id), which is a sequence of 1-255 octets. (alpn-id), which is a sequence of 1-255 octets.
alpn-id = 1*255OCTET alpn-id = 1*255OCTET
For "alpn", the presentation value SHALL be a comma-separated list For "alpn", the presentation value SHALL be a comma-separated list
(Appendix A.1) of one or more alpn-ids. Zone file implementations (Appendix A.1) of one or more alpn-ids. Zone-file implementations
MAY disallow the "," and "\" characters instead of implementing the MAY disallow the "," and "\" characters in ALPN IDs instead of
value-list escaping procedure, relying on the opaque key format (e.g. implementing the value-list escaping procedure, relying on the opaque
key1=\002h2) in the event that these characters are needed. key format (e.g., key1=\002h2) in the event that these characters are
needed.
The wire format value for "alpn" consists of at least one alpn-id The wire-format value for "alpn" consists of at least one alpn-id
prefixed by its length as a single octet, and these length-value prefixed by its length as a single octet, and these length-value
pairs are concatenated to form the SvcParamValue. These pairs MUST pairs are concatenated to form the SvcParamValue. These pairs MUST
exactly fill the SvcParamValue; otherwise, the SvcParamValue is exactly fill the SvcParamValue; otherwise, the SvcParamValue is
malformed. malformed.
For "no-default-alpn", the presentation and wire format values MUST For "no-default-alpn", the presentation and wire-format values MUST
be empty. When "no-default-alpn" is specified in an RR, "alpn" must be empty. When "no-default-alpn" is specified in an RR, "alpn" must
also be specified in order for the RR to be "self-consistent" also be specified in order for the RR to be "self-consistent"
(Section 2.4.3). (Section 2.4.3).
Each scheme that uses this SvcParamKey defines a "default set" of Each scheme that uses this SvcParamKey defines a "default set" of
ALPNs that are supported by nearly all clients and servers, which MAY ALPN IDs that are supported by nearly all clients and servers; this
be empty. To determine the SVCB ALPN set, the client starts with the set MAY be empty. To determine the SVCB ALPN set, the client starts
list of alpn-ids from the "alpn" SvcParamKey, and adds the default with the list of alpn-ids from the "alpn" SvcParamKey, and it adds
set unless the "no-default-alpn" SvcParamKey is present. the default set unless the "no-default-alpn" SvcParamKey is present.
7.1.2. Use 7.1.2. Use
To establish a connection to the endpoint, clients MUST To establish a connection to the endpoint, clients MUST
1. Let SVCB-ALPN-Intersection be the set of protocols in the SVCB 1. Let SVCB-ALPN-Intersection be the set of protocols in the SVCB
ALPN set that the client supports. ALPN set that the client supports.
2. Let Intersection-Transports be the set of transports (e.g. TLS, 2. Let Intersection-Transports be the set of transports (e.g., TLS,
DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection. DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection.
3. For each transport in Intersection-Transports, construct a 3. For each transport in Intersection-Transports, construct a
ProtocolNameList containing the Identification Sequences of all ProtocolNameList containing the Identification Sequences of all
the client's supported ALPN protocols for that transport, without the client's supported ALPN protocols for that transport, without
regard to the SVCB ALPN set. regard to the SVCB ALPN set.
For example, if the SVCB ALPN set is ["http/1.1", "h3"], and the For example, if the SVCB ALPN set is ["http/1.1", "h3"] and the
client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could
attempt to connect using TLS over TCP with a ProtocolNameList of attempt to connect using TLS over TCP with a ProtocolNameList of
["http/1.1", "h2"], and could also attempt a connection using QUIC, ["http/1.1", "h2"] and could also attempt a connection using QUIC
with a ProtocolNameList of ["h3"]. with a ProtocolNameList of ["h3"].
Once the client has constructed a ClientHello, protocol negotiation Once the client has constructed a ClientHello, protocol negotiation
in that handshake proceeds as specified in [ALPN], without regard to in that handshake proceeds as specified in [ALPN], without regard to
the SVCB ALPN set. the SVCB ALPN set.
Clients MAY implement a fallback procedure, using a less-preferred Clients MAY implement a fallback procedure, using a less-preferred
transport if more-preferred transports fail to connect. This transport if more-preferred transports fail to connect. This
fallback behavior is vulnerable to manipulation by a network attacker fallback behavior is vulnerable to manipulation by a network attacker
who blocks the more-preferred transports, but it may be necessary for who blocks the more-preferred transports, but it may be necessary for
compatibility with existing networks. compatibility with existing networks.
With this procedure in place, an attacker who can modify DNS and With this procedure in place, an attacker who can modify DNS and
network traffic can prevent a successful transport connection, but network traffic can prevent a successful transport connection but
cannot otherwise interfere with ALPN protocol selection. This cannot otherwise interfere with ALPN protocol selection. This
procedure also ensures that each ProtocolNameList includes at least procedure also ensures that each ProtocolNameList includes at least
one protocol from the SVCB ALPN set. one protocol from the SVCB ALPN set.
Clients SHOULD NOT attempt connection to a service endpoint whose Clients SHOULD NOT attempt connection to a service endpoint whose
SVCB ALPN set does not contain any supported protocols. SVCB ALPN set does not contain any supported protocols.
To ensure consistency of behavior, clients MAY reject the entire SVCB To ensure consistency of behavior, clients MAY reject the entire SVCB
RRSet and fall back to basic connection establishment if all of the RRset and fall back to basic connection establishment if all of the
compatible RRs indicate "no-default-alpn", even if connection could compatible RRs indicate "no-default-alpn", even if connection could
have succeeded using a non-default alpn. have succeeded using a non-default ALPN protocol.
Zone operators SHOULD ensure that at least one RR in each RRSet Zone operators SHOULD ensure that at least one RR in each RRset
supports the default transports. This enables compatibility with the supports the default transports. This enables compatibility with the
greatest number of clients. greatest number of clients.
7.2. "port" 7.2. "port"
The "port" SvcParamKey defines the TCP or UDP port that should be The "port" SvcParamKey defines the TCP or UDP port that should be
used to reach this alternative endpoint. If this key is not present, used to reach this alternative endpoint. If this key is not present,
clients SHALL use the authority endpoint's port number. clients SHALL use the authority endpoint's port number.
The presentation value of the SvcParamValue is a single decimal The presentation value of the SvcParamValue is a single decimal
integer between 0 and 65535 in ASCII. Any other value (e.g. an empty integer between 0 and 65535 in ASCII. Any other value (e.g., an
value) is a syntax error. To enable simpler parsing, this SvcParam empty value) is a syntax error. To enable simpler parsing, this
MUST NOT contain escape sequences. SvcParamValue MUST NOT contain escape sequences.
The wire format of the SvcParamValue is the corresponding 2 octet The wire format of the SvcParamValue is the corresponding 2-octet
numeric value in network byte order. numeric value in network byte order.
If a port-restricting firewall is in place between some client and If a port-restricting firewall is in place between some client and
the service endpoint, changing the port number might cause that the service endpoint, changing the port number might cause that
client to lose access to the service, so operators should exercise client to lose access to the service, so operators should exercise
caution when using this SvcParamKey to specify a non-default port. caution when using this SvcParamKey to specify a non-default port.
7.3. "ipv4hint" and "ipv6hint" 7.3. "ipv4hint" and "ipv6hint"
The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
MAY use to reach the service. If A and AAAA records for TargetName MAY use to reach the service. If A and AAAA records for TargetName
are locally available, the client SHOULD ignore these hints. are locally available, the client SHOULD ignore these hints.
Otherwise, clients SHOULD perform A and/or AAAA queries for Otherwise, clients SHOULD perform A and/or AAAA queries for
TargetName as in Section 3, and clients SHOULD use the IP address in TargetName per Section 3, and clients SHOULD use the IP address in
those responses for future connections. Clients MAY opt to terminate those responses for future connections. Clients MAY opt to terminate
any connections using the addresses in hints and instead switch to any connections using the addresses in hints and instead switch to
the addresses in response to the TargetName query. Failure to use A the addresses in response to the TargetName query. Failure to use A
and/or AAAA response addresses could negatively impact load balancing and/or AAAA response addresses could negatively impact load balancing
or other geo-aware features and thereby degrade client performance. or other geo-aware features and thereby degrade client performance.
The presentation value SHALL be a comma-separated list (Appendix A.1) The presentation value SHALL be a comma-separated list (Appendix A.1)
of one or more IP addresses of the appropriate family in standard of one or more IP addresses of the appropriate family in standard
textual format [RFC5952][RFC4001]. To enable simpler parsing, this textual format [RFC5952] [RFC4001]. To enable simpler parsing, this
SvcParamValue MUST NOT contain escape sequences. SvcParamValue MUST NOT contain escape sequences.
The wire format for each parameter is a sequence of IP addresses in The wire format for each parameter is a sequence of IP addresses in
network byte order (for the respective address-family). Like an A or network byte order (for the respective address family). Like an A or
AAAA RRSet, the list of addresses represents an unordered collection, AAAA RRset, the list of addresses represents an unordered collection,
and clients SHOULD pick addresses to use in a random order. An empty and clients SHOULD pick addresses to use in a random order. An empty
list of addresses is invalid. list of addresses is invalid.
When selecting between IPv4 and IPv6 addresses to use, clients may When selecting between IPv4 and IPv6 addresses to use, clients may
use an approach such as Happy Eyeballs [HappyEyeballsV2]. When only use an approach such as Happy Eyeballs [HappyEyeballsV2]. When only
"ipv4hint" is present, NAT64 clients may synthesize IPv6 addresses as "ipv4hint" is present, NAT64 clients may synthesize IPv6 addresses as
specified in [RFC7050] or ignore the "ipv4hint" key and wait for AAAA specified in [RFC7050] or ignore the "ipv4hint" key and wait for AAAA
resolution (Section 3). For best performance, server operators resolution (Section 3). For best performance, server operators
SHOULD include an "ipv6hint" parameter whenever they include an SHOULD include an "ipv6hint" parameter whenever they include an
"ipv4hint" parameter. "ipv4hint" parameter.
These parameters are intended to minimize additional connection These parameters are intended to minimize additional connection
latency when a recursive resolver is not compliant with the latency when a recursive resolver is not compliant with the
requirements in Section 4, and SHOULD NOT be included if most clients requirements in Section 4 and SHOULD NOT be included if most clients
are using compliant recursive resolvers. When TargetName is the are using compliant recursive resolvers. When TargetName is the
origin hostname or the owner name (which can be written as "."), service name or the owner name (which can be written as "."), server
server operators SHOULD NOT include these hints, because they are operators SHOULD NOT include these hints, because they are unlikely
unlikely to convey any performance benefit. to convey any performance benefit.
7.4. "mandatory" 7.4. "mandatory"
See Section 8. See Section 8.
8. ServiceMode RR compatibility and mandatory keys 8. ServiceMode RR Compatibility and Mandatory Keys
In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
RR will not function correctly for clients that ignore this RR will not function correctly for clients that ignore this
SvcParamKey. Each SVCB protocol mapping SHOULD specify a set of keys SvcParamKey. Each SVCB protocol mapping SHOULD specify a set of keys
that are "automatically mandatory", i.e. mandatory if they are that are "automatically mandatory", i.e., mandatory if they are
present in an RR. The SvcParamKey "mandatory" is used to indicate present in an RR. The SvcParamKey "mandatory" is used to indicate
any mandatory keys for this RR, in addition to any automatically any mandatory keys for this RR, in addition to any automatically
mandatory keys that are present. mandatory keys that are present.
A ServiceMode RR is considered "compatible" by a client if the client A ServiceMode RR is considered "compatible" by a client if the client
recognizes all the mandatory keys, and their values indicate that recognizes all the mandatory keys and their values indicate that
successful connection establishment is possible. If the SVCB RRSet successful connection establishment is possible. Incompatible RRs
contains no compatible RRs, the client will generally act as if the are ignored (see step 5 of the procedure defined in Section 3).
RRSet is empty.
The presentation value SHALL be a comma-separated list (Appendix A.1) The presentation value SHALL be a comma-separated list (Appendix A.1)
of one or more valid SvcParamKeys, either by their registered name or of one or more valid SvcParamKeys, either by their registered name or
in the unknown-key format (Section 2.1). Keys MAY appear in any in the unknown-key format (Section 2.1). Keys MAY appear in any
order, but MUST NOT appear more than once. For self-consistency order but MUST NOT appear more than once. For self-consistency
(Section 2.4.3), listed keys MUST also appear in the SvcParams. (Section 2.4.3), listed keys MUST also appear in the SvcParams.
To enable simpler parsing, this SvcParamValue MUST NOT contain escape To enable simpler parsing, this SvcParamValue MUST NOT contain escape
sequences. sequences.
For example, the following is a valid list of SvcParams: For example, the following is a valid list of SvcParams:
ipv6hint=... key65333=ex1 key65444=ex2 mandatory=key65444,ipv6hint ipv6hint=... key65333=ex1 key65444=ex2 mandatory=key65444,ipv6hint
In wire format, the keys are represented by their numeric values in In wire format, the keys are represented by their numeric values in
network byte order, concatenated in strictly increasing numeric network byte order, concatenated in strictly increasing numeric
order. order.
This SvcParamKey is always automatically mandatory, and MUST NOT This SvcParamKey is always automatically mandatory and MUST NOT
appear in its own value-list. Other automatically mandatory keys appear in its own value-list. Other automatically mandatory keys
SHOULD NOT appear in the list either. (Including them wastes space SHOULD NOT appear in the list either. (Including them wastes space
and otherwise has no effect.) and otherwise has no effect.)
9. Using Service Bindings with HTTP 9. Using Service Bindings with HTTP
Use of any protocol with SVCB requires a protocol-specific mapping The use of any protocol with SVCB requires a protocol-specific
specification. This section specifies the mapping for the "http" and mapping specification. This section specifies the mapping for the
"https" URI schemes [HTTP]. "http" and "https" URI schemes [HTTP].
To enable special handling for HTTP use-cases, the HTTPS RR type is To enable special handling for HTTP use cases, the HTTPS RR type is
defined as a SVCB-compatible RR type, specific to the "https" and defined as a SVCB-compatible RR type, specific to the "https" and
"http" schemes. Clients MUST NOT perform SVCB queries or accept SVCB "http" schemes. Clients MUST NOT perform SVCB queries or accept SVCB
responses for "https" or "http" schemes. responses for "https" or "http" schemes.
The presentation format of the record is: The presentation format of the record is:
Name TTL IN HTTPS SvcPriority TargetName SvcParams Name TTL IN HTTPS SvcPriority TargetName SvcParams
All the SvcParamKeys defined in Section 7 are permitted for use in All the SvcParamKeys defined in Section 7 are permitted for use in
HTTPS RRs. The default set of ALPN IDs is the single value HTTPS RRs. The default set of ALPN IDs is the single value
"http/1.1". The "automatically mandatory" keys (Section 8) are "http/1.1". The "automatically mandatory" keys (Section 8) are
"port" and "no-default-alpn". (As described in Section 8, clients "port" and "no-default-alpn". (As described in Section 8, clients
must either implement these keys or ignore any RR in which they must either implement these keys or ignore any RR in which they
appear.) Clients that restrict the destination port in "https" URIs appear.) Clients that restrict the destination port in "https" URIs
(e.g. using the "bad ports" list from [FETCH]) SHOULD apply the same (e.g., using the "bad ports" list from [FETCH]) SHOULD apply the same
restriction to the "port" SvcParam. restriction to the "port" SvcParam.
The presence of an HTTPS RR for an origin also indicates that clients The presence of an HTTPS RR for an origin also indicates that clients
should connect securely and use the "https" scheme, as discussed in should connect securely and use the "https" scheme, as discussed in
Section 9.5. This allows HTTPS RRs to apply to pre-existing "http" Section 9.5. This allows HTTPS RRs to apply to pre-existing "http"
scheme URLs, while ensuring that the client uses a secure and scheme URLs, while ensuring that the client uses a secure and
authenticated connection. authenticated connection.
The HTTPS RR parallels the concepts introduced in the HTTP The HTTPS RR parallels the concepts introduced in "HTTP Alternative
Alternative Services proposed standard [AltSvc]. Clients and servers Services" [AltSvc]. Clients and servers that implement HTTPS RRs are
that implement HTTPS RRs are not required to implement Alt-Svc. not required to implement Alt-Svc.
9.1. Query names for HTTPS RRs 9.1. Query Names for HTTPS RRs
The HTTPS RR uses Port Prefix Naming (Section 2.3), with one The HTTPS RR uses Port Prefix Naming (Section 2.3), with one
modification: if the scheme is "https" and the port is 443, then the modification: if the scheme is "https" and the port is 443, then the
client's original QNAME is equal to the service name (i.e. the client's original QNAME is equal to the service name (i.e., the
origin's hostname), without any prefix labels. origin's hostname), without any prefix labels.
By removing the Attrleaf labels [Attrleaf] used in SVCB, this By removing the Attrleaf labels [Attrleaf] used in SVCB, this
construction enables offline DNSSEC signing of wildcard domains, construction enables offline DNSSEC signing of wildcard domains,
which are commonly used with HTTP. Using the service name as the which are commonly used with HTTP. Using the service name as the
owner name of the HTTPS record, without prefixes, also allows the owner name of the HTTPS record, without prefixes, also allows the
targets of existing CNAME chains (e.g. CDN hosts) to start returning targets of existing CNAME chains (e.g., CDN hosts) to start returning
HTTPS RR responses without requiring origin domains to configure and HTTPS RR responses without requiring origin domains to configure and
maintain an additional delegation. maintain an additional delegation.
Following of HTTPS AliasMode RRs and CNAME aliases is unchanged from The procedure for following HTTPS AliasMode RRs and CNAME aliases is
SVCB. unchanged from SVCB (as described in Sections 2.4.2 and 3).
Clients always convert "http" URLs to "https" before performing an Clients always convert "http" URLs to "https" before performing an
HTTPS RR query using the process described in Section 9.5, so domain HTTPS RR query using the process described in Section 9.5, so domain
owners MUST NOT publish HTTPS RRs with a prefix of "_http". owners MUST NOT publish HTTPS RRs with a prefix of "_http".
Note that none of these forms alter the HTTPS origin or authority. Note that none of these forms alter the HTTPS origin or authority.
For example, clients MUST continue to validate TLS certificate For example, clients MUST continue to validate TLS certificate
hostnames based on the origin. hostnames based on the origin.
9.2. Comparison with Alt-Svc 9.2. Comparison with Alt-Svc
Publishing a ServiceMode HTTPS RR in DNS is intended to be similar to Publishing a ServiceMode HTTPS RR in DNS is intended to be similar to
transmitting an Alt-Svc field value over HTTP, and receiving an HTTPS transmitting an Alt-Svc field value over HTTP, and receiving an HTTPS
RR is intended to be similar to receiving that field value over HTTP. RR is intended to be similar to receiving that field value over HTTP.
However, there are some differences in the intended client and server However, there are some differences in the intended client and server
behavior. behavior.
9.2.1. ALPN usage 9.2.1. ALPN Usage
Unlike Alt-Svc Field Values, HTTPS RRs can contain multiple ALPN IDs. Unlike Alt-Svc field values, HTTPS RRs can contain multiple ALPN IDs.
The meaning and use of these IDs is discussed in Section 7.1.2. The meaning and use of these IDs are discussed in Section 7.1.2.
9.2.2. Untrusted channel 9.2.2. Untrusted Channels
HTTPS records do not require or provide any assurance of HTTPS records do not require or provide any assurance of
authenticity. (DNSSEC signing and verification, which would provide authenticity. (DNSSEC signing and verification, which would provide
such assurance, are OPTIONAL.) The DNS resolution process is modeled such assurance, are OPTIONAL.) The DNS resolution process is modeled
as an untrusted channel that might be controlled by an attacker, so as an untrusted channel that might be controlled by an attacker, so
Alt-Svc parameters that cannot be safely received in this model MUST Alt-Svc parameters that cannot be safely received in this model MUST
NOT have a corresponding defined SvcParamKey. For example, there is NOT have a corresponding defined SvcParamKey. For example, there is
no SvcParamKey corresponding to the Alt-Svc "persist" parameter, no SvcParamKey corresponding to the Alt-Svc "persist" parameter,
because this parameter is not safe to accept over an untrusted because this parameter is not safe to accept over an untrusted
channel. channel.
9.2.3. Cache lifetime 9.2.3. Cache Lifetime
There is no SvcParamKey corresponding to the Alt-Svc "ma" (max age) There is no SvcParamKey corresponding to the Alt-Svc "ma" (max age)
parameter. Instead, server operators encode the expiration time in parameter. Instead, server operators encode the expiration time in
the DNS TTL. the DNS TTL.
The appropriate TTL value might be different from the "ma" value used The appropriate TTL value might be different from the "ma" value used
for Alt-Svc, depending on the desired efficiency and agility. Some for Alt-Svc, depending on the desired efficiency and agility. Some
DNS caches incorrectly extend the lifetime of DNS records beyond the DNS caches incorrectly extend the lifetime of DNS records beyond the
stated TTL, so server operators cannot rely on HTTPS RRs expiring on stated TTL, so server operators cannot rely on HTTPS RRs expiring on
time. Shortening the TTL to compensate for incorrect caching is NOT time. Shortening the TTL to compensate for incorrect caching is NOT
RECOMMENDED, as this practice impairs the performance of correctly RECOMMENDED, as this practice impairs the performance of correctly
functioning caches and does not guarantee faster expiration from functioning caches and does not guarantee faster expiration from
incorrect caches. Instead, server operators SHOULD maintain incorrect caches. Instead, server operators SHOULD maintain
compatibility with expired records until they observe that nearly all compatibility with expired records until they observe that nearly all
connections have migrated to the new configuration. connections have migrated to the new configuration.
9.2.4. Granularity 9.2.4. Granularity
Sending Alt-Svc over HTTP allows the server to tailor the Alt-Svc Sending Alt-Svc over HTTP allows the server to tailor the Alt-Svc
Field Value specifically to the client. When using an HTTPS RR, field value specifically to the client. When using an HTTPS RR,
groups of clients will necessarily receive the same SvcParams. groups of clients will necessarily receive the same SvcParams.
Therefore, HTTPS RRs are not suitable for uses that require single- Therefore, HTTPS RRs are not suitable for uses that require single-
client granularity. client granularity.
9.3. Interaction with Alt-Svc 9.3. Interaction with Alt-Svc
Clients that implement support for both Alt-Svc and HTTPS records and Clients that implement support for both Alt-Svc and HTTPS records and
are making a connection based on a cached Alt-Svc response SHOULD are making a connection based on a cached Alt-Svc response SHOULD
retrieve any HTTPS records for the Alt-Svc alt-authority, and ensure retrieve any HTTPS records for the Alt-Svc alt-authority and ensure
that their connection attempts are consistent with both the Alt-Svc that their connection attempts are consistent with both the Alt-Svc
parameters and any received HTTPS SvcParams. If present, the HTTPS parameters and any received HTTPS SvcParams. If present, the HTTPS
record's TargetName and port are used for connection establishment record's TargetName and port are used for connection establishment
(as in Section 3). For example, suppose that "https://example.com" (per Section 3). For example, suppose that "https://example.com"
sends an Alt-Svc field value of: sends an Alt-Svc field value of:
Alt-Svc: h2="alt.example:443", h2="alt2.example:443", h3=":8443" Alt-Svc: h2="alt.example:443", h2="alt2.example:443", h3=":8443"
The client would retrieve the following HTTPS records: The client would retrieve the following HTTPS records:
alt.example. IN HTTPS 1 . alpn=h2,h3 foo=... alt.example. IN HTTPS 1 . alpn=h2,h3 foo=...
alt2.example. IN HTTPS 1 alt2b.example. alpn=h3 foo=... alt2.example. IN HTTPS 1 alt2b.example. alpn=h3 foo=...
_8443._https.example.com. IN HTTPS 1 alt3.example. ( _8443._https.example.com. IN HTTPS 1 alt3.example. (
port=9443 alpn=h2,h3 foo=... ) port=9443 alpn=h2,h3 foo=... )
skipping to change at page 28, line 50 skipping to change at line 1306
* HTTP/2 to alt.example:443 * HTTP/2 to alt.example:443
* HTTP/3 to alt3.example:9443 * HTTP/3 to alt3.example:9443
* Fallback to the client's non-Alt-Svc connection behavior * Fallback to the client's non-Alt-Svc connection behavior
The following connection attempts would not be allowed: The following connection attempts would not be allowed:
* HTTP/3 to alt.example:443 (not consistent with Alt-Svc) * HTTP/3 to alt.example:443 (not consistent with Alt-Svc)
* Any connection to alt2b.example (no ALPN consistent with both the * Any connection to alt2b.example (no ALPN ID consistent with both
HTTPS record and Alt-Svc) the HTTPS record and Alt-Svc)
* HTTPS over TCP to any port on alt3.example (not consistent with * HTTPS over TCP to any port on alt3.example (not consistent with
Alt-Svc) Alt-Svc)
Suppose that "foo" is a SvcParamKey that renders the client SVCB- Suppose that "foo" is a SvcParamKey that renders the client SVCB-
reliant. The following Alt-Svc-only connection attempts would be reliant. The following Alt-Svc-only connection attempts would be
allowed only if the client does not support "foo", as they rely on allowed only if the client does not support "foo", as they rely on
SVCB-optional fallback behavior: SVCB-optional fallback behavior:
* HTTP/2 to alt2.example:443 * HTTP/2 to alt2.example:443
* HTTP/3 to example.com:8443 * HTTP/3 to example.com:8443
Alt-authorities SHOULD carry the same SvcParams as the origin unless Alt-authorities SHOULD carry the same SvcParams as the origin unless
a deviation is specifically known to be safe. As noted in a deviation is specifically known to be safe. As noted in
Section 2.4 of [AltSvc], clients MAY disallow any Alt-Svc connection Section 2.4 of [AltSvc], clients MAY disallow any Alt-Svc connection
according to their own criteria, e.g. disallowing Alt-Svc connections according to their own criteria, e.g., disallowing Alt-Svc
that lack support for privacy features that are available on the connections that lack support for privacy features that are available
origin endpoint. on the authority endpoint.
9.4. Requiring Server Name Indication 9.4. Requiring Server Name Indication
Clients MUST NOT use an HTTPS RR response unless the client supports Clients MUST NOT use an HTTPS RR response unless the client supports
TLS Server Name Indication (SNI) and indicates the origin name in the the TLS Server Name Indication (SNI) extension and indicates the
TLS ClientHello (which might be encrypted via a future specification origin name in the TLS ClientHello (which might be encrypted via a
such as ECH). This supports the conservation of IP addresses. future specification such as [ECH]). This supports the conservation
of IP addresses.
Note that the TLS SNI (and also the HTTP "Host" or ":authority") will Note that the TLS SNI (and also the HTTP "Host" or ":authority") will
indicate the origin, not the TargetName. indicate the origin, not the TargetName.
9.5. HTTP Strict Transport Security 9.5. HTTP Strict Transport Security (HSTS)
An HTTPS RR directs the client to communicate with this host only An HTTPS RR directs the client to communicate with this host only
over a secure transport, similar to HTTP Strict Transport Security over a secure transport, similar to HSTS [HSTS]. Prior to making an
[HSTS]. Prior to making an "http" scheme request, the client SHOULD "http" scheme request, the client SHOULD perform a lookup to
perform a lookup to determine if any HTTPS RRs exist for that origin. determine if any HTTPS RRs exist for that origin. To do so, the
To do so, the client SHOULD construct a corresponding "https" URL as client SHOULD construct a corresponding "https" URL as follows:
follows:
1. Replace the "http" scheme with "https". 1. Replace the "http" scheme with "https".
2. If the "http" URL explicitly specifies port 80, specify port 443. 2. If the "http" URL explicitly specifies port 80, specify port 443.
3. Do not alter any other aspect of the URL. 3. Do not alter any other aspect of the URL.
This construction is equivalent to Section 8.3 of [HSTS], point 5. This construction is equivalent to Section 8.3 of [HSTS], Step 5.
If an HTTPS RR query for this "https" URL returns any AliasMode HTTPS If an HTTPS RR query for this "https" URL returns any AliasMode HTTPS
RRs, or any compatible ServiceMode HTTPS RRs (see Section 8), the RRs or any compatible ServiceMode HTTPS RRs (see Section 8), the
client SHOULD behave as if it has received an HTTP 307 (Temporary client SHOULD behave as if it has received an HTTP 307 (Temporary
Redirect) status code with this "https" URL in the "Location" field. Redirect) status code with this "https" URL in the "Location" field.
(Receipt of an incompatible ServiceMode RR does not trigger the (Receipt of an incompatible ServiceMode RR does not trigger the
redirect behavior.) Because HTTPS RRs are received over an often- redirect behavior.) Because HTTPS RRs are received over an often-
insecure channel (DNS), clients MUST NOT place any more trust in this insecure channel (DNS), clients MUST NOT place any more trust in this
signal than if they had received a 307 (Temporary Redirect) response signal than if they had received a 307 (Temporary Redirect) response
over cleartext HTTP. over cleartext HTTP.
Publishing an HTTPS RR has the potential to have unexpected results Publishing an HTTPS RR can potentially lead to unexpected results or
or a loss in functionality in cases where the "http" resource neither a loss in functionality in cases where the "http" resource neither
redirects to the "https" resource nor references the same underlying redirects to the "https" resource nor references the same underlying
resource. resource.
When an "https" connection fails due to an error in the underlying When an "https" connection fails due to an error in the underlying
secure transport, such as an error in certificate validation, some secure transport, such as an error in certificate validation, some
clients currently offer a "user recourse" that allows the user to clients currently offer a "user recourse" that allows the user to
bypass the security error and connect anyway. When making an "https" bypass the security error and connect anyway. When making an "https"
scheme request to an origin with an HTTPS RR, either directly or via scheme request to an origin with an HTTPS RR, either directly or via
the above redirect, such a client MAY remove the user recourse the above redirect, such a client MAY remove the user recourse
option. Origins that publish HTTPS RRs therefore MUST NOT rely on option. Origins that publish HTTPS RRs therefore MUST NOT rely on
user recourse for access. For more information, see Section 8.4 and user recourse for access. For more information, see Sections 8.4 and
Section 12.1 of [HSTS]. 12.1 of [HSTS].
9.6. Use of HTTPS RRs in other protocols 9.6. Use of HTTPS RRs in Other Protocols
All HTTP connections to named origins are eligible to use HTTPS RRs, All HTTP connections to named origins are eligible to use HTTPS RRs,
even when HTTP is used as part of another protocol or without an even when HTTP is used as part of another protocol or without an
explicit HTTP URL. For example, clients that support HTTPS RRs and explicit HTTP-related URI scheme (Section 4.2 of [HTTP]). For
implement the altered WebSocket [WebSocket] opening handshake from example, clients that support HTTPS RRs and implement [WebSocket]
the W3C Fetch specification [FETCH] SHOULD use HTTPS RRs for the using the altered opening handshake from [FETCH-WEBSOCKETS] SHOULD
requestURL. use HTTPS RRs for the requestURL.
When HTTP is used in a context where URLs or redirects are not When HTTP is used in a context where URLs or redirects are not
applicable (e.g. connections to an HTTP proxy), clients that find a applicable (e.g., connections to an HTTP proxy), clients that find a
corresponding HTTPS RR SHOULD implement a security upgrade behavior corresponding HTTPS RR SHOULD implement security upgrade behavior
equivalent to the one specified in Section 9.5. equivalent to that specified in Section 9.5.
Such protocols MAY define their own SVCB mappings, which MAY be Such protocols MAY define their own SVCB mappings, which MAY be
defined to take precedence over HTTPS RRs. defined to take precedence over HTTPS RRs.
10. Zone Structures 10. Zone Structures
10.1. Structuring zones for flexibility
Each ServiceMode RRSet can only serve a single scheme. The scheme is 10.1. Structuring Zones for Flexibility
Each ServiceMode RRset can only serve a single scheme. The scheme is
indicated by the owner name and the RR type. For the generic SVCB RR indicated by the owner name and the RR type. For the generic SVCB RR
type, this means that each owner name can only be used for a single type, this means that each owner name can only be used for a single
scheme. The underscore prefixing requirement (Section 2.3) ensures scheme. The underscore prefixing requirement (Section 2.3) ensures
that this is true for the initial query, but it is the responsibility that this is true for the initial query, but it is the responsibility
of zone owners to choose names that satisfy this constraint when of zone owners to choose names that satisfy this constraint when
using aliases, including CNAME and AliasMode records. using aliases, including CNAME and AliasMode records.
When using the generic SVCB RR type with aliasing, zone owners SHOULD When using the generic SVCB RR type with aliasing, zone owners SHOULD
choose alias target names that indicate the scheme in use (e.g. choose alias target names that indicate the scheme in use (e.g.,
foosvc.example.net for foo:// schemes). This will help to avoid "foosvc.example.net" for "foo" schemes). This will help to avoid
confusion when another scheme needs to be added to the configuration. confusion when another scheme needs to be added to the configuration.
When multiple port numbers are in use, it may be helpful to repeat When multiple port numbers are in use, it may be helpful to repeat
the prefix labels in the alias target name (e.g. the prefix labels in the alias target name (e.g.,
_1234._foo.svc.example.net). "_1234._foo.svc.example.net").
10.2. Structuring zones for performance 10.2. Structuring Zones for Performance
To avoid a delay for clients using a nonconforming recursive To avoid a delay for clients using a non-conforming recursive
resolver, domain owners SHOULD minimize the use of AliasMode records, resolver, domain owners SHOULD minimize the use of AliasMode records
and SHOULD choose TargetName according to a predictable convention and SHOULD choose TargetName according to a predictable convention
that is known to the client, so that clients can issue A and/or AAAA that is known to the client, so that clients can issue A and/or AAAA
queries for TargetName in advance (see Section 5). Unless otherwise queries for TargetName in advance (see Section 5). Unless otherwise
specified, the convention is to set TargetName to the service name specified, the convention is to set TargetName to the service name
for an initial ServiceMode record, or to "." if it is reached via an for an initial ServiceMode record, or to "." if it is reached via an
alias. alias.
$ORIGIN example.com. ; Origin $ORIGIN example.com. ; Origin
foo 3600 IN CNAME foosvc.example.net. foo 3600 IN CNAME foosvc.example.net.
_8080._foo.foo 3600 IN CNAME foosvc.example.net. _8080._foo.foo 3600 IN CNAME foosvc.example.net.
bar 300 IN AAAA 2001:db8::2 bar 300 IN AAAA 2001:db8::2
_9090._bar.bar 3600 IN SVCB 1 bar key65444=... _9090._bar.bar 3600 IN SVCB 1 bar key65444=...
$ORIGIN example.net. ; Service provider zone $ORIGIN example.net. ; Service provider zone
foosvc 3600 IN SVCB 1 . key65333=... foosvc 3600 IN SVCB 1 . key65333=...
foosvc 300 IN AAAA 2001:db8::1 foosvc 300 IN AAAA 2001:db8::1
Figure 1: foo://foo.example.com:8080 is delegated to Figure 1: "foo://foo.example.com:8080" Is Available at
foosvc.example.net, but bar://bar.example.com:9090 is served "foosvc.example.net", but "bar://bar.example.com:9090" Is Served
locally. Locally
Domain owners SHOULD avoid using a TargetName that is below a DNAME, Domain owners SHOULD avoid using a TargetName that is below a DNAME,
as this is likely unnecessary and makes responses slower and larger. as this is likely unnecessary and makes responses slower and larger.
Also, zone structures that require following more than 8 aliases Also, zone structures that require following more than eight aliases
(counting both AliasMode and CNAME records) are NOT RECOMMENDED. (counting both AliasMode and CNAME records) are NOT RECOMMENDED.
10.3. Operational considerations 10.3. Operational Considerations
Note that some implementations may not allow A or AAAA records on Some authoritative DNS servers may not allow A or AAAA records on
names starting with an underscore due to various interpretations of names starting with an underscore (e.g., [BIND-CHECK-NAMES]). This
RFCs. This could be an operational issue when the TargetName could create an operational issue when the TargetName contains an
contains an attrleaf label, as well as using an TargetName of "." Attrleaf label, or when using a TargetName of "." if the owner name
when the owner name contains an attrleaf label. contains an Attrleaf label.
10.4. Examples 10.4. Examples
10.4.1. Protocol enhancements 10.4.1. Protocol Enhancements
Consider a simple zone of the form: Consider a simple zone of the form:
$ORIGIN simple.example. ; Simple example zone $ORIGIN simple.example. ; Simple example zone
@ 300 IN A 192.0.2.1 @ 300 IN A 192.0.2.1
AAAA 2001:db8::1 AAAA 2001:db8::1
The domain owner could add this record: The domain owner could add this record:
@ 7200 IN HTTPS 1 . alpn=h3 @ 7200 IN HTTPS 1 . alpn=h3
to indicate that https://simple.example supports QUIC in addition to This record would indicate that "https://simple.example" supports
HTTP/1.1 over TLS over TCP (the implicit default). The record could QUIC in addition to HTTP/1.1 over TLS over TCP (the implicit
also include other information (e.g. non-standard port). For default). The record could also include other information (e.g., a
https://simple.example:8443, the record would be: non-standard port). For "https://simple.example:8443", the record
would be:
_8443._https 7200 IN HTTPS 1 . alpn=h3 _8443._https 7200 IN HTTPS 1 . alpn=h3
These records also respectively tell clients to replace the scheme These records also respectively tell clients to replace the scheme
with "https" when loading http://simple.example or with "https" when loading "http://simple.example" or
http://simple.example:8443. "http://simple.example:8443".
10.4.2. Apex aliasing 10.4.2. Apex Aliasing
Consider a zone that is using CNAME aliasing: Consider a zone that is using CNAME aliasing:
$ORIGIN aliased.example. ; A zone that is using a hosting service $ORIGIN aliased.example. ; A zone that is using a hosting service
; Subdomain aliased to a high-performance server pool ; Subdomain aliased to a high-performance server pool
www 7200 IN CNAME pool.svc.example. www 7200 IN CNAME pool.svc.example.
; Apex domain on fixed IPs because CNAME is not allowed at the apex ; Apex domain on fixed IPs because CNAME is not allowed at the apex
@ 300 IN A 192.0.2.1 @ 300 IN A 192.0.2.1
IN AAAA 2001:db8::1 IN AAAA 2001:db8::1
skipping to change at page 33, line 15 skipping to change at line 1507
With this record in place, HTTPS-RR-aware clients will use the same With this record in place, HTTPS-RR-aware clients will use the same
server pool for aliased.example and www.aliased.example. (They will server pool for aliased.example and www.aliased.example. (They will
also upgrade "http://aliased.example/..." to "https".) Non-HTTPS-RR- also upgrade "http://aliased.example/..." to "https".) Non-HTTPS-RR-
aware clients will just ignore the new record. aware clients will just ignore the new record.
Similar to CNAME, HTTPS RRs have no impact on the origin name. When Similar to CNAME, HTTPS RRs have no impact on the origin name. When
connecting, clients will continue to treat the authoritative origins connecting, clients will continue to treat the authoritative origins
as "https://www.aliased.example" and "https://aliased.example", as "https://www.aliased.example" and "https://aliased.example",
respectively, and will validate TLS server certificates accordingly. respectively, and will validate TLS server certificates accordingly.
10.4.3. Parameter binding 10.4.3. Parameter Binding
Suppose that svc.example's primary server pool supports HTTP/3, but Suppose that svc.example's primary server pool supports HTTP/3 but
its backup server pool does not. This can be expressed in the its backup server pool does not. This can be expressed in the
following form: following form:
$ORIGIN svc.example. ; A hosting provider. $ORIGIN svc.example. ; A hosting provider
pool 7200 IN HTTPS 1 . alpn=h2,h3 pool 7200 IN HTTPS 1 . alpn=h2,h3
HTTPS 2 backup alpn=h2 port=8443 HTTPS 2 backup alpn=h2 port=8443
pool 300 IN A 192.0.2.2 pool 300 IN A 192.0.2.2
AAAA 2001:db8::2 AAAA 2001:db8::2
backup 300 IN A 192.0.2.3 backup 300 IN A 192.0.2.3
AAAA 2001:db8::3 AAAA 2001:db8::3
This configuration is entirely compatible with the "Apex aliasing" This configuration is entirely compatible with the "apex aliasing"
example, whether the client supports HTTPS RRs or not. If the client example, whether the client supports HTTPS RRs or not. If the client
does support HTTPS RRs, all connections will be upgraded to HTTPS, does support HTTPS RRs, all connections will be upgraded to HTTPS,
and clients will use HTTP/3 if they can. Parameters are "bound" to and clients will use HTTP/3 if they can. Parameters are "bound" to
each server pool, so each server pool can have its own protocol, port each server pool, so each server pool can have its own protocol, port
number, etc. number, etc.
10.4.4. Multi-CDN 10.4.4. Multi-CDN Configuration
The HTTPS RR is intended to support HTTPS services operated by The HTTPS RR is intended to support HTTPS services operated by
multiple independent entities, such as different Content Delivery multiple independent entities, such as different CDNs or different
Networks (CDNs) or different hosting providers. This includes the hosting providers. This includes the case where a service is
case where a service is migrated from one operator to another, as migrated from one operator to another, as well as the case where the
well as the case where the service is multiplexed between multiple service is multiplexed between multiple operators for performance,
operators for performance, redundancy, etc. redundancy, etc.
This example shows such a configuration, with www.customer.example This example shows such a configuration, with www.customer.example
having different DNS responses to different queries, either over time having different DNS responses to different queries, either over time
or due to logic within the authoritative DNS server: or due to logic within the authoritative DNS server:
; This zone contains/returns different CNAME records ; This zone contains/returns different CNAME records
; at different points-in-time. The RRset for "www" can ; at different points in time. The RRset for "www" can
; only ever contain a single CNAME. ; only ever contain a single CNAME.
; Sometimes the zone has: ; Sometimes the zone has:
$ORIGIN customer.example. ; A Multi-CDN customer domain $ORIGIN customer.example. ; A multi-CDN customer domain
www 900 IN CNAME cdn1.svc1.example. www 900 IN CNAME cdn1.svc1.example.
; and other times it contains: ; and other times it contains:
$ORIGIN customer.example. $ORIGIN customer.example.
www 900 IN CNAME customer.svc2.example. www 900 IN CNAME customer.svc2.example.
; and yet other times it contains: ; and yet other times it contains:
$ORIGIN customer.example. $ORIGIN customer.example.
www 900 IN CNAME cdn3.svc3.example. www 900 IN CNAME cdn3.svc3.example.
; With the following remaining constant and always included: ; With the following remaining constant and always included:
$ORIGIN customer.example. ; A Multi-CDN customer domain $ORIGIN customer.example. ; A multi-CDN customer domain
; The apex is also aliased to www to match its configuration ; The apex is also aliased to www to match its configuration.
@ 7200 IN HTTPS 0 www @ 7200 IN HTTPS 0 www
; Non-HTTPS-aware clients use non-CDN IPs ; Non-HTTPS-aware clients use non-CDN IPs.
A 203.0.113.82 A 203.0.113.82
AAAA 2001:db8:203::2 AAAA 2001:db8:203::2
; Resolutions following the cdn1.svc1.example ; Resolutions following the cdn1.svc1.example
; path use these records. ; path use these records.
; This CDN uses a different alternative service for HTTP/3. ; This CDN uses a different alternative service for HTTP/3.
$ORIGIN svc1.example. ; domain for CDN 1 $ORIGIN svc1.example. ; domain for CDN 1
cdn1 1800 IN HTTPS 1 h3pool alpn=h3 cdn1 1800 IN HTTPS 1 h3pool alpn=h3
HTTPS 2 . alpn=h2 HTTPS 2 . alpn=h2
A 192.0.2.2 A 192.0.2.2
skipping to change at page 35, line 4 skipping to change at line 1589
$ORIGIN svc2.example. ; domain operated by CDN 2 $ORIGIN svc2.example. ; domain operated by CDN 2
customer 300 IN HTTPS 1 . alpn=h2 customer 300 IN HTTPS 1 . alpn=h2
60 IN A 198.51.100.2 60 IN A 198.51.100.2
A 198.51.100.3 A 198.51.100.3
A 198.51.100.4 A 198.51.100.4
AAAA 2001:db8:198::7 AAAA 2001:db8:198::7
AAAA 2001:db8:198::12 AAAA 2001:db8:198::12
; Resolutions following the cdn3.svc3.example ; Resolutions following the cdn3.svc3.example
; path use these records. ; path use these records.
; Note that this CDN has no HTTPS records. ; Note that this CDN has no HTTPS records.
$ORIGIN svc3.example. ; domain operated by CDN 3 $ORIGIN svc3.example. ; domain operated by CDN 3
cdn3 60 IN A 203.0.113.8 cdn3 60 IN A 203.0.113.8
AAAA 2001:db8:113::8 AAAA 2001:db8:113::8
Note that in the above example, the different CDNs have different Note that in the above example, the different CDNs have different
configurations and different capabilities, but clients will use HTTPS configurations and different capabilities, but clients will use HTTPS
RRs as a bound-together unit. RRs as a bound-together unit.
Domain owners should be cautious when using a multi-CDN Domain owners should be cautious when using a multi-CDN
configuration, as it introduces a number of complexities highlighted configuration, as it introduces a number of complexities highlighted
by this example: by this example:
* If CDN 1 supports a desired protocol or feature, and CDN 2 does * If CDN 1 supports a desired protocol or feature and CDN 2 does
not, the client is vulnerable to downgrade by a network adversary not, the client is vulnerable to downgrade by a network adversary
who forces clients to get CDN 2 records. who forces clients to get CDN 2 records.
* Aliasing the apex to its subdomain simplifies the zone file but * Aliasing the apex to its subdomain simplifies the zone file but
likely increases resolution latency, especially when using a non- likely increases resolution latency, especially when using a non-
HTTPS-aware recursive resolver. An alternative would be to alias HTTPS-aware recursive resolver. An alternative would be to alias
the zone apex directly to a name managed by a CDN. the zone apex directly to a name managed by a CDN.
* The A, AAAA, and HTTPS resolutions are independent lookups, so * The A, AAAA, and HTTPS resolutions are independent lookups, so
resolvers may observe and follow different CNAMEs to different resolvers may observe and follow different CNAMEs to different
CDNs. Clients may thus find that the A and AAAA responses do not CDNs. Clients may thus find that the A and AAAA responses do not
correspond to the TargetName in the HTTPS response, and will need correspond to the TargetName in the HTTPS response; these clients
to perform additional queries to retrieve the correct IP will need to perform additional queries to retrieve the correct IP
addresses. Including ipv6hint and ipv4hint will reduce the addresses. Including ipv6hint and ipv4hint will reduce the
performance impact of this case. performance impact of this case.
* If not all CDNs publish HTTPS records, clients will sometimes * If not all CDNs publish HTTPS records, clients will sometimes
receive NODATA for HTTPS queries (as with cdn3.svc3.example receive NODATA for HTTPS queries (as with cdn3.svc3.example above)
above), but could receive A/AAAA records from a different CDN. but could receive A/AAAA records from a different CDN. Clients
Clients will attempt to connect to this CDN without the benefit of will attempt to connect to this CDN without the benefit of its
its HTTPS records. HTTPS records.
10.4.5. Non-HTTP uses 10.4.5. Non-HTTP Uses
For protocols other than HTTP, the SVCB RR and an Attrleaf label For protocols other than HTTP, the SVCB RR and an Attrleaf label
[Attrleaf] will be used. For example, to reach an example resource [Attrleaf] will be used. For example, to reach an example resource
of "baz://api.example.com:8765", the following SVCB record would be of "baz://api.example.com:8765", the following SVCB record would be
used to alias it to "svc4-baz.example.net." which in-turn could used to alias it to "svc4-baz.example.net.", which in turn could
return AAAA/A records and/or SVCB records in ServiceMode: return AAAA/A records and/or SVCB records in ServiceMode:
_8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net. _8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
HTTPS RRs use similar Attrleaf labels if the origin contains a non- HTTPS RRs use similar Attrleaf labels if the origin contains a non-
default port. default port.
11. Interaction with other standards 11. Interaction with Other Standards
This standard is intended to reduce connection latency and improve This standard is intended to reduce connection latency and improve
user privacy. Server operators implementing this standard SHOULD user privacy. Server operators implementing this standard SHOULD
also implement TLS 1.3 [RFC8446] and OCSP Stapling [RFC6066], both of also implement TLS 1.3 [RFC8446] and Online Certificate Status
which confer substantial performance and privacy benefits when used Protocol (OCSP) Stapling (i.e., Certificate Status Request in
in combination with SVCB records. Section 8 of [RFC6066]), both of which confer substantial performance
and privacy benefits when used in combination with SVCB records.
To realize the greatest privacy benefits, this proposal is intended To realize the greatest privacy benefits, this proposal is intended
for use over a privacy-preserving DNS transport (like DNS over TLS for use over a privacy-preserving DNS transport (like DNS over TLS
[DoT] or DNS over HTTPS [DoH]). However, performance improvements, [DoT] or DNS over HTTPS [DoH]). However, performance improvements,
and some modest privacy improvements, are possible without the use of and some modest privacy improvements, are possible without the use of
those standards. those standards.
Any specification for use of SVCB with a protocol MUST have an entry Any specification for the use of SVCB with a protocol MUST have an
for its scheme under the SVCB RR type in the IANA DNS Underscore entry for its scheme under the SVCB RR type in the IANA DNS
Global Scoped Entry Registry [Attrleaf]. The scheme MUST have an "Underscored and Globally Scoped DNS Node Names" registry [Attrleaf].
entry in the IANA URI Schemes Registry [RFC7595], and MUST have a The scheme MUST have an entry in the "Uniform Resource Identifier
defined specification for use with SVCB. (URI) Schemes" registry [RFC7595] and MUST have a defined
specification for use with SVCB.
12. Security Considerations 12. Security Considerations
SVCB/HTTPS RRs permit distribution over untrusted channels, and SVCB/HTTPS RRs permit distribution over untrusted channels, and
clients are REQUIRED to verify that the alternative endpoint is clients are REQUIRED to verify that the alternative endpoint is
authoritative for the service (similar to Section 2.1 of [AltSvc]). authoritative for the service (similar to Section 2.1 of [AltSvc]).
Therefore, DNSSEC signing and validation are OPTIONAL for publishing Therefore, DNSSEC signing and validation are OPTIONAL for publishing
and using SVCB and HTTPS RRs. and using SVCB and HTTPS RRs.
Clients MUST ensure that their DNS cache is partitioned for each Clients MUST ensure that their DNS cache is partitioned for each
skipping to change at page 36, line 45 skipping to change at line 1680
adversary in one network from implanting a forged DNS record that adversary in one network from implanting a forged DNS record that
allows them to track users or hinder their connections after they allows them to track users or hinder their connections after they
leave that network. leave that network.
An attacker who can prevent SVCB resolution can deny clients any An attacker who can prevent SVCB resolution can deny clients any
associated security benefits. A hostile recursive resolver can associated security benefits. A hostile recursive resolver can
always deny service to SVCB queries, but network intermediaries can always deny service to SVCB queries, but network intermediaries can
often prevent resolution as well, even when the client and recursive often prevent resolution as well, even when the client and recursive
resolver validate DNSSEC and use a secure transport. These downgrade resolver validate DNSSEC and use a secure transport. These downgrade
attacks can prevent the "https" upgrade provided by the HTTPS RR attacks can prevent the "https" upgrade provided by the HTTPS RR
(Section 9.5), and disable any other protections coordinated via (Section 9.5) and can disable any other protections coordinated via
SvcParams. To prevent downgrades, Section 3.1 recommends that SvcParams. To prevent downgrades, Section 3.1 recommends that
clients abandon the connection attempt when such an attack is clients abandon the connection attempt when such an attack is
detected. detected.
A hostile DNS intermediary might forge AliasMode "." records A hostile DNS intermediary might forge AliasMode "." records
(Section 2.5.1) as a way to block clients from accessing particular (Section 2.5.1) as a way to block clients from accessing particular
services. Such an adversary could already block entire domains by services. Such an adversary could already block entire domains by
forging erroneous responses, but this mechanism allows them to target forging erroneous responses, but this mechanism allows them to target
particular protocols or ports within a domain. Clients that might be particular protocols or ports within a domain. Clients that might be
subject to such attacks SHOULD ignore AliasMode "." records. subject to such attacks SHOULD ignore AliasMode "." records.
A hostile DNS intermediary or origin can return SVCB records A hostile DNS intermediary or authoritative server can return SVCB
indicating any IP address and port number, including IP addresses records indicating any IP address and port number, including IP
inside the local network and port numbers assigned to internal addresses inside the local network and port numbers assigned to
services. If the attacker can influence the client's payload (e.g. internal services. If the attacker can influence the client's
TLS session ticket contents), and an internal service has a payload (e.g., TLS session ticket contents) and an internal service
sufficiently lax parser, it's possible that the attacker could gain has a sufficiently lax parser, the attacker could gain access to the
unintended access. (The same concerns apply to SRV records, HTTP internal service. (The same concerns apply to SRV records, HTTP Alt-
Alt-Svc, and HTTP redirects.) As a mitigation, SVCB mapping Svc, and HTTP redirects.) As a mitigation, SVCB mapping documents
documents SHOULD indicate any port number restrictions that are SHOULD indicate any port number restrictions that are appropriate for
appropriate for the supported transports. the supported transports.
13. Privacy Considerations 13. Privacy Considerations
Standard address queries reveal the user's intent to access a Standard address queries reveal the user's intent to access a
particular domain. This information is visible to the recursive particular domain. This information is visible to the recursive
resolver, and to many other parties when plaintext DNS transport is resolver, and to many other parties when plaintext DNS transport is
used. SVCB queries, like queries for SRV records and other specific used. SVCB queries, like queries for SRV records and other specific
RR types, additionally reveal the user's intent to use a particular RR types, additionally reveal the user's intent to use a particular
protocol. This is not normally sensitive information, but it should protocol. This is not normally sensitive information, but it should
be considered when adding SVCB support in a new context. be considered when adding SVCB support in a new context.
14. IANA Considerations 14. IANA Considerations
14.1. SVCB RRType 14.1. SVCB RR Type
This document defines a new DNS RR type, SVCB, whose value 64 has
been allocated by IANA from the "Resource Record (RR) TYPEs" registry
on the "Domain Name System (DNS) Parameters" page:
* Type: SVCB
* Value: 64
* Meaning: General Purpose Service Binding
* Reference: This document
14.2. HTTPS RRType IANA has registered the following new DNS RR type in the "Resource
Record (RR) TYPEs" registry on the "Domain Name System (DNS)
Parameters" page:
This document defines a new DNS RR type, "HTTPS", whose value 65 has Type: SVCB
been allocated by IANA from the "Resource Record (RR) TYPEs" registry Value: 64
on the "Domain Name System (DNS) Parameters" page: Meaning: General-purpose service binding
Reference: RFC 9460
* Type: HTTPS 14.2. HTTPS RR Type
* Value: 65
* Meaning: Service Binding type for use with HTTP IANA has registered the following new DNS RR type in the "Resource
Record (RR) TYPEs" registry on the "Domain Name System (DNS)
Parameters" page:
* Reference: This document Type: HTTPS
Value: 65
Meaning: SVCB-compatible type for use with HTTP
Reference: RFC 9460
14.3. New registry for Service Parameters 14.3. New Registry for Service Parameters
IANA is requested to create a new registry, entitled "Service IANA has created the "Service Parameter Keys (SvcParamKeys)" registry
Parameter Keys (SvcParamKeys)". This registry defines the namespace in the "Domain Name System (DNS) Parameters" category on a new page
for parameters, including string representations and numeric entitled "DNS Service Bindings (SVCB)". This registry defines the
SvcParamKey values. This registry is shared with other SVCB- namespace for parameters, including string representations and
numeric SvcParamKey values. This registry is shared with other SVCB-
compatible RR types, such as the HTTPS RR. compatible RR types, such as the HTTPS RR.
ACTION: create this registry, on a new page entitled "DNS Service
Bindings (SVCB)" under the "Domain Name System (DNS) Parameters"
category.
14.3.1. Procedure 14.3.1. Procedure
A registration MUST include the following fields: A registration MUST include the following fields:
* Number: wire format numeric identifier (range 0-65535) Number: Wire-format numeric identifier (range 0-65535)
Name: Unique presentation name
* Name: unique presentation name Meaning: A short description
Reference: Location of specification or registration source
* Meaning: a short description Change Controller: Person or entity, with contact information if
appropriate
* Format Reference: pointer to specification text
* Change Controller: Person or entity, with contact information if
appropriate.
The characters in the registered Name MUST be lower-case alphanumeric The characters in the registered Name field entry MUST be lowercase
or "-" (Section 2.1). The name MUST NOT start with "key" or alphanumeric or "-" (Section 2.1). The name MUST NOT start with
"invalid". "key" or "invalid".
New entries in this registry are subject to an Expert Review The registration policy for new entries is Expert Review ([RFC8126],
registration policy ([RFC8126], Section 4.5). The designated expert Section 4.5). The designated expert MUST ensure that the reference
MUST ensure that the Format Reference is stable and publicly is stable and publicly available and that it specifies how to convert
available, and that it specifies how to convert the SvcParamValue's the SvcParamValue's presentation format to wire format. The
presentation format to wire format. The Format Reference MAY be any reference MAY be any individual's Internet-Draft or a document from
individual's Internet-Draft, or a document from any other source with any other source with similar assurances of stability and
similar assurances of stability and availability. An entry MAY availability. An entry MAY specify a reference of the form "Same as
specify a Format Reference of the form "Same as (other key Name)" if (other key name)" if it uses the same presentation and wire formats
it uses the same presentation and wire formats as an existing key. as an existing key.
This arrangement supports the development of new parameters while This arrangement supports the development of new parameters while
ensuring that zone files can be made interoperable. ensuring that zone files can be made interoperable.
14.3.2. Initial contents 14.3.2. Initial Contents
The "Service Binding (SVCB) Parameter Registry" shall initially be The "Service Parameter Keys (SvcParamKeys)" registry has been
populated with the registrations below: populated with the following initial registrations:
+=============+=================+=============+=========+==========+ +===========+=================+================+=========+==========+
| Number | Name | Meaning |Format |Change | |Number | Name | Meaning |Reference|Change |
| | | |Reference|Controller| | | | | |Controller|
+=============+=================+=============+=========+==========+ +===========+=================+================+=========+==========+
| 0 | mandatory | Mandatory |(This |IETF | |0 | mandatory | Mandatory |RFC 9460,|IETF |
| | | keys in |document)| | | | | keys in this |Section 8| |
| | | this RR |Section 8| | | | | RR | | |
+-------------+-----------------+-------------+---------+----------+ +-----------+-----------------+----------------+---------+----------+
| 1 | alpn | Additional |(This |IETF | |1 | alpn | Additional |RFC 9460,|IETF |
| | | supported |document)| | | | | supported |Section | |
| | | protocols |Section | | | | | protocols |7.1 | |
| | | |7.1 | | +-----------+-----------------+----------------+---------+----------+
+-------------+-----------------+-------------+---------+----------+ |2 | no-default-alpn | No support |RFC 9460,|IETF |
| 2 | no-default-alpn | No support |(This |IETF | | | | for default |Section | |
| | | for default |document)| | | | | protocol |7.1 | |
| | | protocol |Section | | +-----------+-----------------+----------------+---------+----------+
| | | |7.1 | | |3 | port | Port for |RFC 9460,|IETF |
+-------------+-----------------+-------------+---------+----------+ | | | alternative |Section | |
| 3 | port | Port for |(This |IETF | | | | endpoint |7.2 | |
| | | alternative |document)| | +-----------+-----------------+----------------+---------+----------+
| | | endpoint |Section | | |4 | ipv4hint | IPv4 address |RFC 9460,|IETF |
| | | |7.2 | | | | | hints |Section | |
+-------------+-----------------+-------------+---------+----------+ | | | |7.3 | |
| 4 | ipv4hint | IPv4 |(This |IETF | +-----------+-----------------+----------------+---------+----------+
| | | address |document)| | |5 | ech | RESERVED |N/A |IETF |
| | | hints |Section | | | | | (held for | | |
| | | |7.3 | | | | | Encrypted | | |
+-------------+-----------------+-------------+---------+----------+ | | | ClientHello) | | |
| 5 | ech | RESERVED |N/A |IETF | +-----------+-----------------+----------------+---------+----------+
| | | (will be | | | |6 | ipv6hint | IPv6 address |RFC 9460,|IETF |
| | | used for | | | | | | hints |Section | |
| | | ECH) | | | | | | |7.3 | |
+-------------+-----------------+-------------+---------+----------+ +-----------+-----------------+----------------+---------+----------+
| 6 | ipv6hint | IPv6 |(This |IETF | |65280-65534| N/A | Reserved for |RFC 9460 |IETF |
| | | address |document)| | | | | Private Use | | |
| | | hints |Section | | +-----------+-----------------+----------------+---------+----------+
| | | |7.3 | | |65535 | N/A | Reserved |RFC 9460 |IETF |
+-------------+-----------------+-------------+---------+----------+ | | | ("Invalid | | |
| 65280-65534 | N/A | Private Use |(This |IETF | | | | key") | | |
| | | |document)| | +-----------+-----------------+----------------+---------+----------+
+-------------+-----------------+-------------+---------+----------+
| 65535 | N/A | Reserved |(This |IETF |
| | | ("Invalid |document)| |
| | | key") | | |
+-------------+-----------------+-------------+---------+----------+
Table 1 Table 1
14.4. Other registry updates 14.4. Other Registry Updates
Per [Attrleaf], please add the following entry to the DNS Underscore Per [Attrleaf], the following entry has been added to the DNS
Global Scoped Entry Registry: "Underscored and Globally Scoped DNS Node Names" registry:
+=========+============+=================+=================+ +=========+============+===========+
| RR TYPE | _NODE NAME | Meaning | Reference | | RR Type | _NODE NAME | Reference |
+=========+============+=================+=================+ +=========+============+===========+
| HTTPS | _https | HTTPS SVCB info | (This document) | | HTTPS | _https | RFC 9460 |
+---------+------------+-----------------+-----------------+ +---------+------------+-----------+
Table 2 Table 2
15. Acknowledgments and Related Proposals 15. References
There have been a wide range of proposed solutions over the years to
the "CNAME at the Zone Apex" challenge proposed. These include
[I-D.bellis-dnsop-http-record], [I-D.ietf-dnsop-aname], and others.
Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas
Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David
Benjamin, Mark Andrews, Emily Stark, Eric Orth, Kyle Rose, Craig
Taylor, Dan McArdle, Brian Dickson, Willem Toorop, Pieter Lexis,
Puneet Sood, Olivier Poitrey, Mashooq Muhaimen, Tom Carpay, and many
others for their feedback and suggestions on this draft.
16. References
16.1. Normative References 15.1. Normative References
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [ALPN] 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/rfc/rfc7301>. July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[Attrleaf] Crocker, D., "Scoped Interpretation of DNS Resource [Attrleaf] Crocker, D., "Scoped Interpretation of DNS Resource
Records through "Underscored" Naming of Attribute Leaves", Records through "Underscored" Naming of Attribute Leaves",
BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019, BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
<https://www.rfc-editor.org/rfc/rfc8552>. <https://www.rfc-editor.org/info/rfc8552>.
[DoH] Hoffman, P. and P. McManus, "DNS Queries over HTTPS [DoH] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>. <https://www.rfc-editor.org/info/rfc8484>.
[DoT] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., [DoT] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>. 2016, <https://www.rfc-editor.org/info/rfc7858>.
[HappyEyeballsV2] [HappyEyeballsV2]
Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305, Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017, DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/rfc/rfc8305>. <https://www.rfc-editor.org/info/rfc8305>.
[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Semantics", Work in Progress, Internet-Draft, draft-ietf- Ed., "HTTP Semantics", STD 97, RFC 9110,
httpbis-semantics-19, 12 September 2021, DOI 10.17487/RFC9110, June 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis- <https://www.rfc-editor.org/info/rfc9110>.
semantics-19>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/rfc/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and [RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928, L. Jones, "SOCKS Protocol Version 5", RFC 1928,
DOI 10.17487/RFC1928, March 1996, DOI 10.17487/RFC1928, March 1996,
<https://www.rfc-editor.org/rfc/rfc1928>. <https://www.rfc-editor.org/info/rfc1928>.
[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/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997, Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/rfc/rfc2181>. <https://www.rfc-editor.org/info/rfc2181>.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, DOI 10.17487/RFC3225, December 2001, RFC 3225, DOI 10.17487/RFC3225, December 2001,
<https://www.rfc-editor.org/rfc/rfc3225>. <https://www.rfc-editor.org/info/rfc3225>.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, DOI 10.17487/RFC3597, September (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
2003, <https://www.rfc-editor.org/rfc/rfc3597>. 2003, <https://www.rfc-editor.org/info/rfc3597>.
[RFC4001] Daniele, M., Haberman, B., Routhier, S., and J. [RFC4001] Daniele, M., Haberman, B., Routhier, S., and J.
Schoenwaelder, "Textual Conventions for Internet Network Schoenwaelder, "Textual Conventions for Internet Network
Addresses", RFC 4001, DOI 10.17487/RFC4001, February 2005, Addresses", RFC 4001, DOI 10.17487/RFC4001, February 2005,
<https://www.rfc-editor.org/rfc/rfc4001>. <https://www.rfc-editor.org/info/rfc4001>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010, DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/rfc/rfc5952>. <https://www.rfc-editor.org/info/rfc5952>.
[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/rfc/rfc6066>. <https://www.rfc-editor.org/info/rfc6066>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van [RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147, Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011, DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/rfc/rfc6147>. <https://www.rfc-editor.org/info/rfc6147>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of [RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis", the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013, RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/rfc/rfc7050>. <https://www.rfc-editor.org/info/rfc7050>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/rfc/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines [RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35, and Registration Procedures for URI Schemes", BCP 35,
RFC 7595, DOI 10.17487/RFC7595, June 2015, RFC 7595, DOI 10.17487/RFC7595, June 2015,
<https://www.rfc-editor.org/rfc/rfc7595>. <https://www.rfc-editor.org/info/rfc7595>.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W. [RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871, Kumari, "Client Subnet in DNS Queries", RFC 7871,
DOI 10.17487/RFC7871, May 2016, DOI 10.17487/RFC7871, May 2016,
<https://www.rfc-editor.org/rfc/rfc7871>. <https://www.rfc-editor.org/info/rfc7871>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[WebSocket] [WebSocket]
Fette, I. and A. Melnikov, "The WebSocket Protocol", Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011, RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/rfc/rfc6455>. <https://www.rfc-editor.org/info/rfc6455>.
16.2. Informative References 15.2. Informative References
[AltSvc] Nottingham, M., McManus, P., and J. Reschke, "HTTP [AltSvc] 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/rfc/rfc7838>. April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[ANAME-DNS-RR]
Finch, T., Hunt, E., van Dijk, P., Eden, A., and W.
Mekking, "Address-specific DNS aliases (ANAME)", Work in
Progress, Internet-Draft, draft-ietf-dnsop-aname-04, 8
July 2019, <https://datatracker.ietf.org/doc/html/draft-
ietf-dnsop-aname-04>.
[BIND-CHECK-NAMES]
Internet Systems Consortium, "BIND v9.19.11 Configuration
Reference: "check-names"", September 2023,
<https://bind9.readthedocs.io/en/v9.19.11/
reference.html#namedconf-statement-check-names>.
[DNAME] Rose, S. and W. Wijngaards, "DNAME Redirection in the [DNAME] Rose, S. and W. Wijngaards, "DNAME Redirection in the
DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012, DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
<https://www.rfc-editor.org/rfc/rfc6672>. <https://www.rfc-editor.org/info/rfc6672>.
[DNSTerm] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [DNSTerm] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/rfc/rfc8499>. January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[ECH] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS [ECH] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft, Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-15, 3 October 2022, draft-ietf-tls-esni-17, 9 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls- <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
esni-15>. esni-17>.
[FETCH] "Fetch Living Standard", May 2020, [FETCH] WHATWG, "Fetch Living Standard", October 2023,
<https://fetch.spec.whatwg.org/>. <https://fetch.spec.whatwg.org/>.
[FETCH-WEBSOCKETS]
WHATWG, "WebSockets Living Standard", September 2023,
<https://websockets.spec.whatwg.org/>.
[HSTS] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict [HSTS] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797, Transport Security (HSTS)", RFC 6797,
DOI 10.17487/RFC6797, November 2012, DOI 10.17487/RFC6797, November 2012,
<https://www.rfc-editor.org/rfc/rfc6797>. <https://www.rfc-editor.org/info/rfc6797>.
[HTTP3] Bishop, M., "HTTP/3", Work in Progress, Internet-Draft,
draft-ietf-quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
[I-D.bellis-dnsop-http-record] [HTTP-DNS-RR]
Bellis, R., "A DNS Resource Record for HTTP", Work in Bellis, R., "A DNS Resource Record for HTTP", Work in
Progress, Internet-Draft, draft-bellis-dnsop-http-record- Progress, Internet-Draft, draft-bellis-dnsop-http-record-
00, 3 November 2018, 00, 3 November 2018,
<https://datatracker.ietf.org/doc/html/draft-bellis-dnsop- <https://datatracker.ietf.org/doc/html/draft-bellis-dnsop-
http-record-00>. http-record-00>.
[I-D.ietf-dnsop-aname] [HTTP/3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
Finch, T., Hunt, E., van Dijk, P., Eden, A., and W. M. June 2022, <https://www.rfc-editor.org/info/rfc9114>.
Mekking, "Address-specific DNS aliases (ANAME)", Work in
Progress, Internet-Draft, draft-ietf-dnsop-aname-04, 8
July 2019, <https://datatracker.ietf.org/doc/html/draft-
ietf-dnsop-aname-04>.
[RFC1912] Barr, D., "Common DNS Operational and Configuration [RFC1912] Barr, D., "Common DNS Operational and Configuration
Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996, Errors", RFC 1912, DOI 10.17487/RFC1912, February 1996,
<https://www.rfc-editor.org/rfc/rfc1912>. <https://www.rfc-editor.org/info/rfc1912>.
[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/rfc/rfc6454>. <https://www.rfc-editor.org/info/rfc6454>.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000, DOI 10.17487/RFC2782, February 2000,
<https://www.rfc-editor.org/rfc/rfc2782>. <https://www.rfc-editor.org/info/rfc2782>.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
Appendix A. Decoding text in zone files Appendix A. Decoding Text in Zone Files
DNS zone files are capable of representing arbitrary octet sequences DNS zone files are capable of representing arbitrary octet sequences
in basic ASCII text, using various delimiters and encodings. The in basic ASCII text, using various delimiters and encodings,
algorithm for decoding these character-strings is defined in according to an algorithm defined in Section 5.1 of [RFC1035]. The
Section 5.1 of [RFC1035]. Here we summarize the allowed input to following summarizes some allowed inputs to that algorithm, using
that algorithm, using ABNF: ABNF:
; non-special is VCHAR minus DQUOTE, ";", "(", ")", and "\". ; non-special is VCHAR minus DQUOTE, ";", "(", ")", and "\".
non-special = %x21 / %x23-27 / %x2A-3A / %x3C-5B / %x5D-7E non-special = %x21 / %x23-27 / %x2A-3A / %x3C-5B / %x5D-7E
; non-digit is VCHAR minus DIGIT ; non-digit is VCHAR minus DIGIT.
non-digit = %x21-2F / %x3A-7E non-digit = %x21-2F / %x3A-7E
; dec-octet is a number 0-255 as a three-digit decimal number. ; dec-octet is a number 0-255 as a three-digit decimal number.
dec-octet = ( "0" / "1" ) 2DIGIT / dec-octet = ( "0" / "1" ) 2DIGIT /
"2" ( ( %x30-34 DIGIT ) / ( "5" %x30-35 ) ) "2" ( ( %x30-34 DIGIT ) / ( "5" %x30-35 ) )
escaped = "\" ( non-digit / dec-octet ) escaped = "\" ( non-digit / dec-octet )
contiguous = 1*( non-special / escaped ) contiguous = 1*( non-special / escaped )
quoted = DQUOTE *( contiguous / ( ["\"] WSP ) ) DQUOTE quoted = DQUOTE *( contiguous / ( ["\"] WSP ) ) DQUOTE
char-string = contiguous / quoted char-string = contiguous / quoted
The decoding algorithm allows char-string to represent any *OCTET, The decoding algorithm allows char-string to represent any *OCTET,
using quoting to group values (e.g., those with internal whitespace), using quoting to group values (e.g., those with internal whitespace),
and escaping to represent each non-printable octet as a single and escaping to represent each non-printable octet as a single
escaped sequence. In this document, this algorithm is referred to as escaped sequence. In this document, this algorithm is referred to as
"character-string decoding". The algorithm is the same as used by "character-string decoding", because Section 5.1 of [RFC1035] uses
<character-string> in RFC 1035, although the output length in this this algorithm to produce a <character-string>. Note that while the
document is not limited to 255 octets. length of a <character-string> is limited to 255 octets, the
character-string decoding algorithm can produce output of any length.
A.1. Decoding a comma-separated list A.1. Decoding a Comma-Separated List
In order to represent lists of items in zone files, this In order to represent lists of items in zone files, this
specification uses comma-separated lists. When the allowed items in specification uses comma-separated lists. When the allowed items in
the list cannot contain "," or "\", this is trivial. (For the list cannot contain "," or "\", this is trivial. (For
simplicity, empty items are not allowed.) A value-list parser that simplicity, empty items are not allowed.) A value-list parser that
splits on "," and prohibits items containing "\" is sufficient to splits on "," and prohibits items containing "\" is sufficient to
comply with all requirements in this document. This corresponds to comply with all requirements in this document. This corresponds to
the simple-comma-separated syntax: the simple-comma-separated syntax:
; item-allowed is OCTET minus "," and "\". ; item-allowed is OCTET minus "," and "\".
skipping to change at page 47, line 4 skipping to change at line 2092
item = 1*OCTET item = 1*OCTET
escaped-item = 1*(item-allowed / "\," / "\\") escaped-item = 1*(item-allowed / "\," / "\\")
comma-separated = [escaped-item *("," escaped-item)] comma-separated = [escaped-item *("," escaped-item)]
Decoding of value-lists happens after character-string decoding. For Decoding of value-lists happens after character-string decoding. For
example, consider these char-string SvcParamValues: example, consider these char-string SvcParamValues:
"part1,part2,part3\\,part4\\\\" "part1,part2,part3\\,part4\\\\"
part1\,\p\a\r\t2\044part3\092,part4\092\\ part1\,\p\a\r\t2\044part3\092,part4\092\\
These inputs are equivalent: character-string decoding either of them These inputs are equivalent: character-string decoding either of them
would produce the same value: would produce the same value:
part1,part2,part3\,part4\\ part1,part2,part3\,part4\\
Applying comma-separated list decoding to this value would produce a Applying comma-separated list decoding to this value would produce a
list of three items: list of three items:
part1 part1
part2 part2
part3,part4\ part3,part4\
Appendix B. HTTP Mapping Summary Appendix B. HTTP Mapping Summary
This table serves as a non-normative summary of the HTTP mapping for This table serves as a non-normative summary of the HTTP mapping for
SVCB (Section 9). Future protocol mappings may provide a similar SVCB (Section 9). Future protocol mappings may provide a similar
summary table. summary table.
+==========================+======================+ +--------------------------+----------------------+
+==========================+======================+
| *Mapped scheme* | "https" | | *Mapped scheme* | "https" |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *Other affected schemes* | "http", "wss", "ws", | | *Other affected schemes* | "http", "wss", "ws", |
| | (other HTTP-based) | | | (other HTTP-based) |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *RR type* | HTTPS (65) | | *RR type* | HTTPS (65) |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *Name prefix* | None for port 443, | | *Name prefix* | None for port 443, |
| | else _$PORT._https | | | else _$PORT._https |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *Automatically Mandatory | port, no-default- | | *Automatically mandatory | port, no-default- |
| Keys* | alpn | | keys* | alpn |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *SvcParam defaults* | alpn: ["http/1.1"] | | *SvcParam defaults* | alpn: ["http/1.1"] |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *Special behaviors* | HTTP to HTTPS | | *Special behaviors* | Upgrade from HTTP to |
| | upgrade | | | HTTPS |
+--------------------------+----------------------+ +--------------------------+----------------------+
| *Keys that records must | None | | *Keys that records must | None |
| include* | | | include* | |
+--------------------------+----------------------+ +--------------------------+----------------------+
Table 3 Table 3
Appendix C. Comparison with alternatives Appendix C. Comparison with Alternatives
The SVCB and HTTPS RR types closely resemble, and are inspired by, The SVCB and HTTPS RR types closely resemble, and are inspired by,
some existing record types and proposals. A complaint with all of some existing record types and proposals. One complaint regarding
the alternatives is that web clients have seemed unenthusiastic about all of the alternatives is that web clients have seemed
implementing them. The hope here is that by providing an extensible unenthusiastic about implementing them. The hope here is that an
solution that solves multiple problems we will overcome the inertia extensible solution that solves multiple problems will overcome this
and have a path to achieve client implementation. inertia and have a path to achieve client implementation.
C.1. Differences from the SRV RR type C.1. Differences from the SRV RR Type
An SRV record [SRV] can perform a similar function to the SVCB An SRV record [SRV] can perform a function similar to that of the
record, informing a client to look in a different location for a SVCB record, informing a client to look in a different location for a
service. However, there are several differences: service. However, there are several differences:
* SRV records are typically mandatory, whereas SVCB is intended to * SRV records are typically mandatory, whereas SVCB is intended to
be optional when used with pre-existing protocols. be optional when used with pre-existing protocols.
* SRV records cannot instruct the client to switch or upgrade * SRV records cannot instruct the client to switch or upgrade
protocols, whereas SVCB can signal such an upgrade (e.g. to protocols, whereas SVCB can signal such an upgrade (e.g., to
HTTP/2). HTTP/2).
* SRV records are not extensible, whereas SVCB and HTTPS RRs can be * SRV records are not extensible, whereas SVCB and HTTPS RRs can be
extended with new parameters. extended with new parameters.
* SRV records specify a "weight" for unbalanced randomized load- * SRV records specify a "weight" for unbalanced randomized load
balancing. SVCB only supports balanced randomized load-balancing, balancing. SVCB only supports balanced randomized load balancing,
although weights could be added via a future SvcParam. although weights could be added via a future SvcParam.
C.2. Differences from the proposed HTTP record C.2. Differences from the Proposed HTTP Record
Unlike [I-D.bellis-dnsop-http-record], this approach is extensible to Unlike [HTTP-DNS-RR], this approach is extensible to cover Alt-Svc
cover Alt-Svc and Encrypted ClientHello use-cases. Like that and Encrypted ClientHello use cases. Like that proposal, this
proposal, this addresses the zone apex CNAME challenge. addresses the zone-apex CNAME challenge.
Like that proposal, it remains necessary to continue to include Like that proposal, it remains necessary to continue to include
address records at the zone apex for legacy clients. address records at the zone apex for legacy clients.
C.3. Differences from the proposed ANAME record C.3. Differences from the Proposed ANAME Record
Unlike [I-D.ietf-dnsop-aname], this approach is extensible to cover Unlike [ANAME-DNS-RR], this approach is extensible to cover Alt-Svc
Alt-Svc and ECH use-cases. This approach also does not require any and Encrypted ClientHello use cases. This approach also does not
changes or special handling on either authoritative or primary require any changes or special handling on either authoritative or
servers, beyond optionally returning in-bailiwick additional records. primary servers, beyond optionally returning in-bailiwick additional
records.
Like that proposal, this addresses the zone apex CNAME challenge for Like that proposal, this addresses the zone-apex CNAME challenge for
clients that implement this. clients that implement this.
However, with this SVCB proposal, it remains necessary to continue to However, with this SVCB proposal, it remains necessary to continue to
include address records at the zone apex for legacy clients. If include address records at the zone apex for legacy clients. If
deployment of this standard is successful, the number of legacy deployment of this standard is successful, the number of legacy
clients will fall over time. As the number of legacy clients clients will fall over time. As the number of legacy clients
declines, the operational effort required to serve these users declines, the operational effort required to serve these users
without the benefit of SVCB indirection should fall. Server without the benefit of SVCB indirection should fall. Server
operators can easily observe how much traffic reaches this legacy operators can easily observe how much traffic reaches this legacy
endpoint, and may remove the apex's address records if the observed endpoint and may remove the apex's address records if the observed
legacy traffic has fallen to negligible levels. legacy traffic has fallen to negligible levels.
C.4. Comparison with separate RR types for AliasMode and ServiceMode C.4. Comparison with Separate RR Types for AliasMode and ServiceMode
Abstractly, functions of AliasMode and ServiceMode are independent, Abstractly, functions of AliasMode and ServiceMode are independent,
so it might be tempting to specify them as separate RR types. so it might be tempting to specify them as separate RR types.
However, this would result in a serious performance impairment, However, this would result in serious performance impairment, because
because clients cannot rely on their recursive resolver to follow clients cannot rely on their recursive resolver to follow SVCB
SVCB aliases (unlike CNAME). Thus, clients would have to issue aliases (unlike CNAME). Thus, clients would have to issue queries
queries for both RR types in parallel, potentially at each step of for both RR types in parallel, potentially at each step of the alias
the alias chain. Recursive resolvers that implement the chain. Recursive resolvers that implement the specification would,
specification would, upon receipt of a ServiceMode query, emit both a upon receipt of a ServiceMode query, emit both a ServiceMode query
ServiceMode and an AliasMode query to the authoritative. Thus, and an AliasMode query to the authoritative DNS server. Thus,
splitting the RR type would double, or in some cases triple, the load splitting the RR type would double, or in some cases triple, the load
on clients and servers, and would not reduce implementation on clients and servers, and would not reduce implementation
complexity. complexity.
Appendix D. Test vectors Appendix D. Test Vectors
These test vectors only contain the RDATA portion of SVCB/HTTPS These test vectors only contain the RDATA portion of SVCB/HTTPS
records in presentation format, generic format ([RFC3597]) and wire records in presentation format, generic format [RFC3597], and wire
format. The wire format uses hexadecimal (\xNN) for each non-ascii format. The wire format uses hexadecimal (\xNN) for each non-ASCII
byte. As the wireformat is long, it is broken into several lines. byte. As the wire format is long, it is broken into several lines.
D.1. AliasMode D.1. AliasMode
example.com. HTTPS 0 foo.example.com. example.com. HTTPS 0 foo.example.com.
\# 19 ( \# 19 (
00 00 ; priority 00 00 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
) )
skipping to change at page 50, line 4 skipping to change at line 2232
00 00 ; priority 00 00 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
) )
\x00\x00 # priority \x00\x00 # priority
\x03foo\x07example\x03com\x00 # target \x03foo\x07example\x03com\x00 # target
Figure 2: AliasMode Figure 2: AliasMode
D.2. ServiceMode D.2. ServiceMode
example.com. SVCB 1 . example.com. SVCB 1 .
\# 3 ( \# 3 (
00 01 ; priority 00 01 ; priority
00 ; target (root label) 00 ; target (root label)
) )
\x00\x01 # priority \x00\x01 # priority
\x00 # target, root label \x00 # target (root label)
Figure 3: TargetName is "." Figure 3: TargetName Is "."
example.com. SVCB 16 foo.example.com. port=53 example.com. SVCB 16 foo.example.com. port=53
\# 25 ( \# 25 (
00 10 ; priority 00 10 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
00 03 ; key 3 00 03 ; key 3
00 02 ; length 2 00 02 ; length 2
00 35 ; value 00 35 ; value
) )
\x00\x10 # priority \x00\x10 # priority
\x03foo\x07example\x03com\x00 # target \x03foo\x07example\x03com\x00 # target
\x00\x03 # key 3 \x00\x03 # key 3
\x00\x02 # length: 2 bytes \x00\x02 # length 2
\x00\x35 # value \x00\x35 # value
Figure 4: Specifies a port Figure 4: Specifies a Port
example.com. SVCB 1 foo.example.com. key667=hello example.com. SVCB 1 foo.example.com. key667=hello
\# 28 ( \# 28 (
00 01 ; priority 00 01 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
02 9b ; key 667 02 9b ; key 667
00 05 ; length 5 00 05 ; length 5
68 65 6c 6c 6f ; value 68 65 6c 6c 6f ; value
) )
\x00\x01 # priority \x00\x01 # priority
\x03foo\x07example\x03com\x00 # target \x03foo\x07example\x03com\x00 # target
\x02\x9b # key 667 \x02\x9b # key 667
\x00\x05 # length 5 \x00\x05 # length 5
hello # value hello # value
Figure 5: A generic key and unquoted value Figure 5: A Generic Key and Unquoted Value
example.com. SVCB 1 foo.example.com. key667="hello\210qoo" example.com. SVCB 1 foo.example.com. key667="hello\210qoo"
\# 32 ( \# 32 (
00 01 ; priority 00 01 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
02 9b ; key 667 02 9b ; key 667
00 09 ; length 9 00 09 ; length 9
68 65 6c 6c 6f d2 71 6f 6f ; value 68 65 6c 6c 6f d2 71 6f 6f ; value
) )
\x00\x01 # priority \x00\x01 # priority
\x03foo\x07example\x03com\x00 # target \x03foo\x07example\x03com\x00 # target
\x02\x9b # key 667 \x02\x9b # key 667
\x00\x09 # length 9 \x00\x09 # length 9
hello\xd2qoo # value hello\xd2qoo # value
Figure 6: A generic key and quoted value with a decimal escape Figure 6: A Generic Key and Quoted Value with a Decimal Escape
example.com. SVCB 1 foo.example.com. ( example.com. SVCB 1 foo.example.com. (
ipv6hint="2001:db8::1,2001:db8::53:1" ipv6hint="2001:db8::1,2001:db8::53:1"
) )
\# 55 ( \# 55 (
00 01 ; priority 00 01 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
00 06 ; key 6 00 06 ; key 6
00 20 ; length 32 00 20 ; length 32
skipping to change at page 51, line 45 skipping to change at line 2321
\x00\x01 # priority \x00\x01 # priority
\x03foo\x07example\x03com\x00 # target \x03foo\x07example\x03com\x00 # target
\x00\x06 # key 6 \x00\x06 # key 6
\x00\x20 # length 32 \x00\x20 # length 32
\x20\x01\x0d\xb8\x00\x00\x00\x00 \x20\x01\x0d\xb8\x00\x00\x00\x00
\x00\x00\x00\x00\x00\x00\x00\x01 # first address \x00\x00\x00\x00\x00\x00\x00\x01 # first address
\x20\x01\x0d\xb8\x00\x00\x00\x00 \x20\x01\x0d\xb8\x00\x00\x00\x00
\x00\x00\x00\x00\x00\x53\x00\x01 # second address \x00\x00\x00\x00\x00\x53\x00\x01 # second address
Figure 7: Two quoted IPv6 hints Figure 7: Two Quoted IPv6 Hints
example.com. SVCB 1 example.com. ipv6hint="2001:db8:122:344::192.0.2.33"
\# 35 ( example.com. SVCB 1 example.com. (
00 01 ; priority ipv6hint="2001:db8:122:344::192.0.2.33"
07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target )
00 06 ; key 6 \# 35 (
00 10 ; length 16 00 01 ; priority
20 01 0d b8 01 22 03 44 00 00 00 00 c0 00 02 21 ; address 07 65 78 61 6d 70 6c 65 03 63 6f 6d 00 ; target
) 00 06 ; key 6
00 10 ; length 16
20 01 0d b8 01 22 03 44 00 00 00 00 c0 00 02 21 ; address
)
\x00\x01 # priority \x00\x01 # priority
\x07example\x03com\x00 # target \x07example\x03com\x00 # target
\x00\x06 # key 6 \x00\x06 # key 6
\x00\x10 # length 16 \x00\x10 # length 16
\x20\x01\x0d\xb8\x01\x22\x03\x44 \x20\x01\x0d\xb8\x01\x22\x03\x44
\x00\x00\x00\x00\xc0\x00\x02\x21 # address \x00\x00\x00\x00\xc0\x00\x02\x21 # address
Figure 8: An IPv6 hint using the embedded IPv4 syntax Figure 8: An IPv6 Hint Using the Embedded IPv4 Syntax
example.com. SVCB 16 foo.example.org. ( example.com. SVCB 16 foo.example.org. (
alpn=h2,h3-19 mandatory=ipv4hint,alpn alpn=h2,h3-19 mandatory=ipv4hint,alpn
ipv4hint=192.0.2.1 ipv4hint=192.0.2.1
) )
\# 48 ( \# 48 (
00 10 ; priority 00 10 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 ; target
00 00 ; key 0 00 00 ; key 0
skipping to change at page 53, line 44 skipping to change at line 2382
\x00\x01 # key 1 \x00\x01 # key 1
\x00\x09 # param length 9 \x00\x09 # param length 9
\x02 # alpn length 2 \x02 # alpn length 2
h2 # alpn value h2 # alpn value
\x05 # alpn length 5 \x05 # alpn length 5
h3-19 # alpn value h3-19 # alpn value
\x00\x04 # key 4 \x00\x04 # key 4
\x00\x04 # param length 4 \x00\x04 # param length 4
\xc0\x00\x02\x01 # param value \xc0\x00\x02\x01 # param value
Figure 9: SvcParamKey ordering is arbitrary in presentation Figure 9: SvcParamKey Ordering Is Arbitrary in Presentation
format but sorted in wire format Format but Sorted in Wire Format
example.com. SVCB 16 foo.example.org. alpn="f\\\\oo\\,bar,h2" example.com. SVCB 16 foo.example.org. alpn="f\\\\oo\\,bar,h2"
example.com. SVCB 16 foo.example.org. alpn=f\\\092oo\092,bar,h2 example.com. SVCB 16 foo.example.org. alpn=f\\\092oo\092,bar,h2
\# 35 ( \# 35 (
00 10 ; priority 00 10 ; priority
03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 ; target 03 66 6f 6f 07 65 78 61 6d 70 6c 65 03 6f 72 67 00 ; target
00 01 ; key 1 00 01 ; key 1
00 0c ; param length 12 00 0c ; param length 12
08 ; alpn length 8 08 ; alpn length 8
skipping to change at page 54, line 28 skipping to change at line 2408
\x00\x10 # priority \x00\x10 # priority
\x03foo\x07example\x03org\x00 # target \x03foo\x07example\x03org\x00 # target
\x00\x01 # key 1 \x00\x01 # key 1
\x00\x0c # param length 12 \x00\x0c # param length 12
\x08 # alpn length 8 \x08 # alpn length 8
f\oo,bar # alpn value f\oo,bar # alpn value
\x02 # alpn length 2 \x02 # alpn length 2
h2 # alpn value h2 # alpn value
Figure 10: An alpn value with an escaped comma and an escaped Figure 10: An "alpn" Value with an Escaped Comma and an Escaped
backslash in two presentation formats Backslash in Two Presentation Formats
D.3. Failure cases D.3. Failure Cases
This subsection contains test vectors which are not compliant with This subsection contains test vectors that are not compliant with
this document. The various reasons for non-compliance are explained this document. The various reasons for non-compliance are explained
with each example. with each example.
example.com. SVCB 1 foo.example.com. ( example.com. SVCB 1 foo.example.com. (
key123=abc key123=def key123=abc key123=def
) )
Figure 11: Multiple instances of the same SvcParamKey Figure 11: Multiple Instances of the Same SvcParamKey
example.com. SVCB 1 foo.example.com. mandatory example.com. SVCB 1 foo.example.com. mandatory
example.com. SVCB 1 foo.example.com. alpn example.com. SVCB 1 foo.example.com. alpn
example.com. SVCB 1 foo.example.com. port example.com. SVCB 1 foo.example.com. port
example.com. SVCB 1 foo.example.com. ipv4hint example.com. SVCB 1 foo.example.com. ipv4hint
example.com. SVCB 1 foo.example.com. ipv6hint example.com. SVCB 1 foo.example.com. ipv6hint
Figure 12: Missing SvcParamValues that must be nonempty Figure 12: Missing SvcParamValues That Must Be Non-Empty
example.com. SVCB 1 foo.example.com. no-default-alpn=abc example.com. SVCB 1 foo.example.com. no-default-alpn=abc
Figure 13: The "no-default-alpn" SvcParamKey value must be empty
Figure 13: The "no-default-alpn" SvcParamKey Value Must Be Empty
example.com. SVCB 1 foo.example.com. mandatory=key123 example.com. SVCB 1 foo.example.com. mandatory=key123
Figure 14: A mandatory SvcParam is missing Figure 14: A Mandatory SvcParam Is Missing
example.com. SVCB 1 foo.example.com. mandatory=mandatory example.com. SVCB 1 foo.example.com. mandatory=mandatory
Figure 15: The "mandatory" SvcParamKey must not be included in Figure 15: The "mandatory" SvcParamKey Must Not Be Included in
the mandatory list the Mandatory List
example.com. SVCB 1 foo.example.com. ( example.com. SVCB 1 foo.example.com. (
mandatory=key123,key123 key123=abc mandatory=key123,key123 key123=abc
) )
Figure 16: Multiple instances of the same SvcParamKey in the Figure 16: Multiple Instances of the Same SvcParamKey in the
mandatory list Mandatory List
Appendix E. Change history
(This section to be removed by the RFC editor.)
* draft-ietf-dnsop-svcb-https-12
- Split out Encrypted Client Hello (ECH) to a separate draft and
convert all remaining references to informative.
* draft-ietf-dnsop-svcb-https-11
- Narrow set of post-IESG clarifications:
o Clarify that that the fallback addition of the QNAME was for
the AliasMode case
o Note that some implementations may not allow A/AAAA records
on names starting with an underscore
* draft-ietf-dnsop-svcb-https-10
- Clarify rationale for two recommendations
* draft-ietf-dnsop-svcb-https-09
- Extensive adjustments based on IESG reviews, including:
o IANA registry changed to Expert Review policy
o Adjustments to the use of normative language
o Revised and expanded description of HSTS behavior
o Expanded discussion of CNAME handling
o Discussion of SvcParams in AliasMode records
o Restructured ABNF for comma-separated lists
o Additional references and many other minor clarifications
- Other changes include:
o New section on interaction with DNS64
o New text on the interpretation of wildcard owner names
o Adjusted guidance on default ALPN enforcement
o Removed mention of IPv4-mapped IPv6
* draft-ietf-dnsop-svcb-https-08
- Extensive structural and editorial adjustments based on area
reviews, including:
o A new section on SVCB-compatible record types
o Reorganized description of client behavior
o Test vectors are now in titled figures
o Adjusted mapping summary
o Improve description of rules for resolver handling of
invalid SvcParamValues.
- New text on cross-transport fallback (e.g. QUIC vs. TCP)
- Improved explanation of use with domain-oriented transport
proxies
- HTTP terminology adjusted to match draft-ietf-httpbis-semantics
- Improved and corrected IANA instructions
* draft-ietf-dnsop-svcb-https-07
- Editorial improvements following AD review.
* draft-ietf-dnsop-svcb-https-06
- Add requirements for HTTPS origins that also use Alt-Svc
- Remove requirement for comma-escaping related to unusual ALPN
values
- Allow resolvers to reject invalid SvcParamValues, with
additional guidance
* draft-ietf-dnsop-svcb-https-05
- Specify interaction with EDNS Client Subnet and Additional
section caching
- Rename "echconfig" to "ech"
- Add a suite of test vectors (both valid and invalid) and more
examples
- Clarify requirements for resolvers' (non-)use of SvcParams
- Clarify guidance regarding default ALPN values
* draft-ietf-dnsop-svcb-https-04
- Simplify the IANA instructions (pure First Come First Served)
- Recommend against publishing chains of >8 aliases
- Clarify requirements for using SVCB with a transport proxy
- Adjust guidance for Port Prefix Naming
- Minor editorial updates
* draft-ietf-dnsop-svcb-https-03
- Simplified escaping of comma-separated values
- Reorganized client requirements
- Added a warning about port filtering for cross-protocol attacks
- Clarified self-consistency rules for SvcParams
- Added a non-normative mapping summary table for HTTPS
* draft-ietf-dnsop-svcb-https-02
- Added a Privacy Considerations section
- Adjusted resolution fallback description
- Clarified status of SvcParams in AliasMode
- Improved advice on zone structuring and use with Alt-Svc
- Improved examples, including a new Multi-CDN example
- Reorganized text on value-list parsing and SvcPriority
- Improved phrasing and other editorial improvements throughout
* draft-ietf-dnsop-svcb-https-01
- Added a "mandatory" SvcParamKey
- Added the ability to indicate that a service does not exist
- Adjusted resolution and ALPN algorithms
- Major terminology revisions for "origin" and CamelCase names
- Revised ABNF
- Include allocated RR type numbers
- Various corrections, explanations, and recommendations
* draft-ietf-dnsop-svcb-https-00
- Rename HTTPSSVC RR to HTTPS RR
- Rename "an SVCB" to "a SVCB"
- Removed "design considerations and open issues" section and
some other "to be removed" text
* draft-ietf-dnsop-svcb-httpssvc-03
- Revised chain length limit requirements
- Revised IANA registry rules for SvcParamKeys
- Require HTTPS clients to implement SNI
- Update terminology for Encrypted ClientHello
- Clarifications: non-default ports, transport proxies, HSTS
procedure, WebSocket behavior, wire format, IP hints, inner/
outer ClientHello with ECH
- Various textual and ABNF corrections
* draft-ietf-dnsop-svcb-httpssvc-02
- All changes to Alt-Svc have been removed
- Expanded and reorganized examples
- Priority zero is now the definition of AliasForm
- Repeated SvcParamKeys are no longer allowed
- The "=" sign may be omitted in a key=value pair if the value is
also empty
- In the wire format, SvcParamKeys must be in sorted order
- New text regarding how to handle resolution timeouts
- Expanded description of recursive resolver behavior
- Much more precise description of the intended ALPN behavior
- Match the HSTS specification's language on HTTPS enforcement
- Removed 'esniconfig=""' mechanism and simplified ESNI
connection logic
* draft-ietf-dnsop-svcb-httpssvc-01
- Reduce the emphasis on conversion between HTTPSSVC and Alt-Svc
- Make the "untrusted channel" concept more precise.
- Make SvcFieldPriority = 0 the definition of AliasForm, instead
of a requirement.
* draft-ietf-dnsop-svcb-httpssvc-00
- Document an optimization for optimistic pre-connection. (Chris
Wood)
- Relax IP hint handling requirements. (Eric Rescorla)
* draft-nygren-dnsop-svcb-httpssvc-00
- Generalize to an SVCB record, with special-case handling for
Alt-Svc and HTTPS separated out to dedicated sections.
- Split out a separate HTTPSSVC record for the HTTPS use-case.
- Remove the explicit SvcRecordType=0/1 and instead make the
AliasForm vs ServiceForm be implicit. This was based on
feedback recommending against subtyping RR type.
- Remove one optimization.
* draft-nygren-httpbis-httpssvc-03
- Change redirect type for HSTS-style behavior from 302 to 307 to
reduce ambiguities.
* draft-nygren-httpbis-httpssvc-02
- Remove the redundant length fields from the wire format.
- Define a SvcDomainName of "." for SvcRecordType=1 as being the
HTTPSSVC RRNAME.
- Replace "hq" with "h3".
* draft-nygren-httpbis-httpssvc-01
- Fixes of record name. Replace references to "HTTPSVC" with Acknowledgments and Related Proposals
"HTTPSSVC".
* draft-nygren-httpbis-httpssvc-00 Over the years, IETF participants have proposed a wide range of
solutions to the "CNAME at the zone apex" challenge, including
[HTTP-DNS-RR], [ANAME-DNS-RR], and others. The authors are grateful
for their work to elucidate the problem and identify promising
strategies to address it, some of which are reflected in this
document.
- Initial version Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas
Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David
Benjamin, Mark Andrews, Emily Stark, Eric Orth, Kyle Rose, Craig
Taylor, Dan McArdle, Brian Dickson, Willem Toorop, Pieter Lexis,
Puneet Sood, Olivier Poitrey, Mashooq Muhaimen, Tom Carpay, and many
others for their feedback and suggestions on this document.
Authors' Addresses Authors' Addresses
Ben Schwartz Ben Schwartz
Google Meta Platforms, Inc.
Email: ietf@bemasc.net Email: ietf@bemasc.net
Mike Bishop Mike Bishop
Akamai Technologies Akamai Technologies
Email: mbishop@evequefou.be Email: mbishop@evequefou.be
Erik Nygren Erik Nygren
Akamai Technologies Akamai Technologies
Email: erik+ietf@nygren.org Email: erik+ietf@nygren.org
 End of changes. 326 change blocks. 
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