draft-ietf-dnsop-svcb-httpssvc-02.txt   draft-ietf-dnsop-svcb-httpssvc-03.txt 
DNSOP Working Group B. Schwartz DNSOP Working Group B. Schwartz
Internet-Draft Google Internet-Draft Google
Intended status: Standards Track M. Bishop Intended status: Standards Track M. Bishop
Expires: September 10, 2020 E. Nygren Expires: 13 December 2020 E. Nygren
Akamai Technologies Akamai Technologies
March 9, 2020 11 June 2020
Service binding and parameter specification via the DNS (DNS SVCB and Service binding and parameter specification via the DNS (DNS SVCB and
HTTPSSVC) HTTPSSVC)
draft-ietf-dnsop-svcb-httpssvc-02 draft-ietf-dnsop-svcb-httpssvc-03
Abstract Abstract
This document specifies the "SVCB" and "HTTPSSVC" DNS resource record This document specifies the "SVCB" and "HTTPSSVC" DNS resource record
types to facilitate the lookup of information needed to make types to facilitate the lookup of information needed to make
connections for origin resources, such as for HTTPS URLs. SVCB connections for origin resources, such as for HTTPS URLs. SVCB
records allow an origin to be served from multiple network locations, records allow an origin to be served from multiple network locations,
each with associated parameters (such as transport protocol each with associated parameters (such as transport protocol
configuration and keying material for encrypting TLS SNI). They also configuration and keys for encrypting the TLS ClientHello). They
enable aliasing of apex domains, which is not possible with CNAME. also enable aliasing of apex domains, which is not possible with
The HTTPSSVC DNS RR is a variation of SVCB for HTTPS and HTTP CNAME. The HTTPSSVC DNS RR is a variation of SVCB for HTTPS and HTTP
origins. By providing more information to the client before it origins. By providing more information to the client before it
attempts to establish a connection, these records offer potential attempts to establish a connection, these records offer potential
benefits to both performance and privacy. benefits to both performance and privacy.
TO BE REMOVED: This proposal is inspired by and based on recent DNS TO BE REMOVED: This proposal is inspired by and based on recent DNS
usage proposals such as ALTSVC, ANAME, and ESNIKEYS (as well as long usage proposals such as ALTSVC, ANAME, and ESNIKEYS (as well as long
standing desires to have SRV or a functional equivalent implemented standing desires to have SRV or a functional equivalent implemented
for HTTP). These proposals each provide an important function but for HTTP). These proposals each provide an important function but
are potentially incompatible with each other, such as when an origin are potentially incompatible with each other, such as when an origin
is load-balanced across multiple hosting providers (multi-CDN). is load-balanced across multiple hosting providers (multi-CDN).
Furthermore, these each add potential cases for adding additional Furthermore, these each add potential cases for adding additional
record lookups in-addition to AAAA/A lookups. This design attempts record lookups in addition to AAAA/A lookups. This design attempts
to provide a unified framework that encompasses the key functionality to provide a unified framework that encompasses the key functionality
of these proposals, as well as providing some extensibility for of these proposals, as well as providing some extensibility for
addressing similar future challenges. addressing similar future challenges.
TO BE REMOVED: The specific name for this RR type is an open topic TO BE REMOVED: The specific name for this RR type is an open topic
for discussion. "SVCB" and "HTTPSSVC" are meant as placeholders as for discussion. "SVCB" and "HTTPSSVC" are meant as placeholders as
they are easy to replace. Other names might include "B", "SRV2", they are easy to replace. Other names might include "B", "SRV2",
"SVCHTTPS", "HTTPS", and "ALTSVC". "SVCHTTPS", "HTTPS", and "ALTSVC".
TO BE REMOVED: This document is being collaborated on in Github at: TO BE REMOVED: This document is being collaborated on in Github at:
https://github.com/MikeBishop/dns-alt-svc [1]. The most recent https://github.com/MikeBishop/dns-alt-svc
working version of the document, open issues, etc. should all be (https://github.com/MikeBishop/dns-alt-svc). The most recent working
available there. The authors (gratefully) accept pull requests. 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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2020. This Internet-Draft will expire on 13 December 2020.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Example: Protocol enhancements . . . . . . . . . . . . . 5 1.1. Goals of the SVCB RR . . . . . . . . . . . . . . . . . . 5
1.2. Example: Apex aliasing . . . . . . . . . . . . . . . . . 5 1.2. Overview of the SVCB RR . . . . . . . . . . . . . . . . . 6
1.3. Example: Parameter binding . . . . . . . . . . . . . . . 6 1.3. Parameter for Encrypted ClientHello . . . . . . . . . . . 7
1.4. Example: Non-HTTPS uses . . . . . . . . . . . . . . . . . 6 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
1.5. Goals of the SVCB RR . . . . . . . . . . . . . . . . . . 7 2. The SVCB record type . . . . . . . . . . . . . . . . . . . . 8
1.6. Overview of the SVCB RR . . . . . . . . . . . . . . . . . 8 2.1. Presentation format . . . . . . . . . . . . . . . . . . . 8
1.7. Parameter for ESNI . . . . . . . . . . . . . . . . . . . 9 2.1.1. Presentation format for SvcFieldValue key=value
1.8. Terminology . . . . . . . . . . . . . . . . . . . . . . . 9 pairs . . . . . . . . . . . . . . . . . . . . . . . . 8
2. The SVCB record type . . . . . . . . . . . . . . . . . . . . 9 2.2. SVCB RDATA Wire Format . . . . . . . . . . . . . . . . . 10
2.1. Presentation format . . . . . . . . . . . . . . . . . . . 10 2.3. SVCB owner names . . . . . . . . . . . . . . . . . . . . 11
2.1.1. Presentation format for SvcFieldValue key=value pairs 10 2.4. SvcRecordType . . . . . . . . . . . . . . . . . . . . . . 12
2.2. SVCB RDATA Wire Format . . . . . . . . . . . . . . . . . 11 2.5. SVCB records: AliasForm . . . . . . . . . . . . . . . . . 12
2.3. SVCB owner names . . . . . . . . . . . . . . . . . . . . 12 2.6. SVCB records: ServiceForm . . . . . . . . . . . . . . . . 13
2.4. SvcRecordType . . . . . . . . . . . . . . . . . . . . . . 13
2.5. SVCB records: AliasForm . . . . . . . . . . . . . . . . . 13
2.6. SVCB records: ServiceForm . . . . . . . . . . . . . . . . 14
2.6.1. Special handling of "." for SvcDomainName in 2.6.1. Special handling of "." for SvcDomainName in
ServiceForm . . . . . . . . . . . . . . . . . . . . . 14 ServiceForm . . . . . . . . . . . . . . . . . . . . . 13
2.6.2. SvcFieldPriority . . . . . . . . . . . . . . . . . . 14 2.6.2. SvcFieldPriority . . . . . . . . . . . . . . . . . . 13
3. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 14 3. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 14
3.1. Handling resolution failures . . . . . . . . . . . . . . 15 3.1. Handling resolution failures . . . . . . . . . . . . . . 15
3.2. Clients using a Proxy . . . . . . . . . . . . . . . . . . 16 3.2. Clients using a Proxy . . . . . . . . . . . . . . . . . . 15
4. DNS Server Behavior . . . . . . . . . . . . . . . . . . . . . 16 4. DNS Server Behavior . . . . . . . . . . . . . . . . . . . . . 16
4.1. Authoritative servers . . . . . . . . . . . . . . . . . . 16 4.1. Authoritative servers . . . . . . . . . . . . . . . . . . 16
4.2. Recursive resolvers . . . . . . . . . . . . . . . . . . . 16 4.2. Recursive resolvers . . . . . . . . . . . . . . . . . . . 16
4.3. General requirements . . . . . . . . . . . . . . . . . . 17 4.3. General requirements . . . . . . . . . . . . . . . . . . 17
5. Performance optimizations . . . . . . . . . . . . . . . . . . 18 5. Performance optimizations . . . . . . . . . . . . . . . . . . 17
5.1. Optimistic pre-connection and connection reuse . . . . . 18 5.1. Optimistic pre-connection and connection reuse . . . . . 17
5.2. Generating and using incomplete responses . . . . . . . . 18 5.2. Generating and using incomplete responses . . . . . . . . 18
5.3. Structuring zones for performance . . . . . . . . . . . . 19 5.3. Structuring zones for performance . . . . . . . . . . . . 18
6. Initial SvcParamKeys . . . . . . . . . . . . . . . . . . . . 19 6. Initial SvcParamKeys . . . . . . . . . . . . . . . . . . . . 18
6.1. "alpn" and "no-default-alpn" . . . . . . . . . . . . . . 19 6.1. "alpn" and "no-default-alpn" . . . . . . . . . . . . . . 19
6.2. "port" . . . . . . . . . . . . . . . . . . . . . . . . . 21 6.2. "port" . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.3. "esniconfig" . . . . . . . . . . . . . . . . . . . . . . 21 6.3. "echconfig" . . . . . . . . . . . . . . . . . . . . . . . 21
6.4. "ipv4hint" and "ipv6hint" . . . . . . . . . . . . . . . . 21 6.4. "ipv4hint" and "ipv6hint" . . . . . . . . . . . . . . . . 21
7. Using SVCB with HTTPS and HTTP . . . . . . . . . . . . . . . 22 7. Using SVCB with HTTPS and HTTP . . . . . . . . . . . . . . . 22
7.1. Owner names for HTTPSSVC records . . . . . . . . . . . . 23 7.1. Owner names for HTTPSSVC records . . . . . . . . . . . . 22
7.2. Relationship to Alt-Svc . . . . . . . . . . . . . . . . . 23 7.2. Relationship to Alt-Svc . . . . . . . . . . . . . . . . . 23
7.2.1. ALPN usage . . . . . . . . . . . . . . . . . . . . . 23 7.2.1. ALPN usage . . . . . . . . . . . . . . . . . . . . . 23
7.2.2. Untrusted channel . . . . . . . . . . . . . . . . . . 24 7.2.2. Untrusted channel . . . . . . . . . . . . . . . . . . 23
7.2.3. TTL and granularity . . . . . . . . . . . . . . . . . 24 7.2.3. TTL and granularity . . . . . . . . . . . . . . . . . 24
7.3. Interaction with Alt-Svc . . . . . . . . . . . . . . . . 24 7.3. Interaction with Alt-Svc . . . . . . . . . . . . . . . . 24
7.4. HTTP Strict Transport Security . . . . . . . . . . . . . 25 7.4. Requiring Server Name Indication . . . . . . . . . . . . 24
8. SVCB/HTTPSSVC parameter for ESNI keys . . . . . . . . . . . . 25 7.5. HTTP Strict Transport Security . . . . . . . . . . . . . 25
7.6. HTTP-based protocols . . . . . . . . . . . . . . . . . . 25
8. SVCB/HTTPSSVC parameter for ECH configuration . . . . . . . . 26
8.1. Client behavior . . . . . . . . . . . . . . . . . . . . . 26 8.1. Client behavior . . . . . . . . . . . . . . . . . . . . . 26
8.2. Deployment considerations . . . . . . . . . . . . . . . . 26 8.2. Deployment considerations . . . . . . . . . . . . . . . . 27
9. Interaction with other standards . . . . . . . . . . . . . . 26 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10. Security Considerations . . . . . . . . . . . . . . . . . . . 27 9.1. Protocol enhancements . . . . . . . . . . . . . . . . . . 27
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 9.2. Apex aliasing . . . . . . . . . . . . . . . . . . . . . . 27
11.1. New registry for Service Parameters . . . . . . . . . . 27 9.3. Parameter binding . . . . . . . . . . . . . . . . . . . . 28
11.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . 27 9.4. Non-HTTPS uses . . . . . . . . . . . . . . . . . . . . . 28
11.1.2. Initial contents . . . . . . . . . . . . . . . . . . 28 10. Interaction with other standards . . . . . . . . . . . . . . 28
11.2. Registry updates . . . . . . . . . . . . . . . . . . . . 28 11. Security Considerations . . . . . . . . . . . . . . . . . . . 29
12. Acknowledgments and Related Proposals . . . . . . . . . . . . 29 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 12.1. New registry for Service Parameters . . . . . . . . . . 29
13.1. Normative References . . . . . . . . . . . . . . . . . . 29 12.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . 29
13.2. Informative References . . . . . . . . . . . . . . . . . 32 12.1.2. Initial contents . . . . . . . . . . . . . . . . . . 30
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12.2. Registry updates . . . . . . . . . . . . . . . . . . . . 31
Appendix A. Comparison with alternatives . . . . . . . . . . . . 33 13. Acknowledgments and Related Proposals . . . . . . . . . . . . 32
A.1. Differences from the SRV RR type . . . . . . . . . . . . 33 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
A.2. Differences from the proposed HTTP record . . . . . . . . 33 14.1. Normative References . . . . . . . . . . . . . . . . . . 32
A.3. Differences from the proposed ANAME record . . . . . . . 33 14.2. Informative References . . . . . . . . . . . . . . . . . 35
A.4. Differences from the proposed ESNI record . . . . . . . . 34
Appendix B. Design Considerations and Open Issues . . . . . . . 34 Appendix A. Comparison with alternatives . . . . . . . . . . . . 36
B.1. Record Name . . . . . . . . . . . . . . . . . . . . . . . 34 A.1. Differences from the SRV RR type . . . . . . . . . . . . 36
B.2. Generality . . . . . . . . . . . . . . . . . . . . . . . 34 A.2. Differences from the proposed HTTP record . . . . . . . . 37
B.3. Wire Format . . . . . . . . . . . . . . . . . . . . . . . 34 A.3. Differences from the proposed ANAME record . . . . . . . 37
B.4. Whether to include Weight . . . . . . . . . . . . . . . . 35 A.4. Comparison with separate RR types for AliasForm and
Appendix C. Change history . . . . . . . . . . . . . . . . . . . 35 ServiceForm . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 Appendix B. Design Considerations and Open Issues . . . . . . . 38
B.1. Record Name . . . . . . . . . . . . . . . . . . . . . . . 38
B.2. Generality . . . . . . . . . . . . . . . . . . . . . . . 38
B.3. Wire Format . . . . . . . . . . . . . . . . . . . . . . . 38
B.4. Whether to include Weight . . . . . . . . . . . . . . . . 38
Appendix C. Change history . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
1. Introduction 1. Introduction
The SVCB and HTTPSSVC RRs provide clients with complete instructions The SVCB and HTTPSSVC RRs provide clients with complete instructions
for access to an origin. This information enables improved for access to an origin. This information enables improved
performance and privacy by avoiding transient connections to a sub- performance and privacy by avoiding transient connections to a sub-
optimal default server, negotiating a preferred protocol, and optimal default server, negotiating a preferred protocol, and
providing relevant public keys. providing relevant public keys.
For example, when clients need to make a connection to fetch For example, when clients need to make a connection to fetch
resources associated with an HTTPS URI, they currently resolve only A resources associated with an HTTPS URI, they currently resolve only A
and/or AAAA records for the origin hostname. This is adequate for and/or AAAA records for the origin hostname. This is adequate for
services that use basic HTTPS (fixed port, no QUIC, no [ESNI]). services that use basic HTTPS (fixed port, no QUIC, no [ECH]). Going
Going beyond basic HTTPS confers privacy, performance, and beyond basic HTTPS confers privacy, performance, and operational
operational advantages, but it requires the client to learn advantages, but it requires the client to learn additional
additional information, and it is highly desirable to minimize the information, and it is highly desirable to minimize the number of
number of round-trip and lookups required to learn this additional round-trips and lookups required to learn this additional
information. information.
The SVCB and HTTPSSVC RRs also help when the operator of an origin The SVCB and HTTPSSVC RRs also help when the operator of an origin
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 resource "https://example.com" to a e.g. delegating the origin resource "https://example.com" to a
service operator endpoint at "svc.example.net". While this case can service operator endpoint at "svc.example.net". While this case can
sometimes be handled by a CNAME, that does not cover all use-cases. sometimes be handled by a CNAME, that does not cover all use-cases.
CNAME is also inadequate when the service operator needs to provide a CNAME is also inadequate when the service operator needs to provide a
bound collection of consistent configuration parameters through the bound collection of consistent configuration parameters through the
DNS (such as network location, protocol, and keying information). DNS (such as network location, protocol, and keying information).
skipping to change at page 5, line 23 skipping to change at page 5, line 35
RDATA set. RDATA set.
TO BE REMOVED: If we use this for providing configuration for DNS TO BE REMOVED: If we use this for providing configuration for DNS
authorities, it is likely we'd specify a distinct "NS2" RR type that authorities, it is likely we'd specify a distinct "NS2" RR type that
is an instantiation of SVCB for authoritative nameserver delegation is an instantiation of SVCB for authoritative nameserver delegation
and parameter specification, similar to HTTPSSVC. and parameter specification, similar to HTTPSSVC.
TO BE REMOVED: Another open question is whether SVCB records should TO BE REMOVED: Another open question is whether SVCB records should
be self-descriptive and include the service name (eg, "https") in the be self-descriptive and include the service name (eg, "https") in the
RDATA section to avoid ambiguity. Perhaps this could be included as RDATA section to avoid ambiguity. Perhaps this could be included as
a svc="baz" parameter for protocols that are not the default for the an svc="baz" parameter for protocols that are not the default for the
RR type? Current inclination is to not do so. RR type? Current inclination is to not do so.
1.1. Example: Protocol enhancements 1.1. Goals of the SVCB RR
Consider a simple zone of the form
simple.example. 300 IN A 192.0.2.1
AAAA 2001:db8::1
The domain owner could add a record like
simple.example. 7200 IN HTTPSSVC 1 . alpn=h3 ...
The presence of this record indicates to clients that simple.example
supports HTTPS, and the key=value pairs indicate that it supports
QUIC in addition to HTTPS over TLS (an implicit default). The record
could also include other information (e.g. non-standard port, ESNI
configuration).
1.2. Example: Apex aliasing
Consider a zone that is using CNAME aliasing:
$ORIGIN aliased.example. ; A zone that is using a hosting service
; Subdomain aliased to a high-performance server pool
www 7200 IN CNAME pool.svc.example.
; Apex domain on fixed IPs because CNAME is not allowed at the apex
. 300 IN A 192.0.2.1
IN AAAA 2001:db8::1
With HTTPSSVC, the owner of aliased.example could alias the apex by
adding one additional record:
. 7200 IN HTTPSSVC 0 pool.svc.example.
With this record in place, HTTPSSVC-aware clients will use the same
server pool for aliased.example and www.aliased.example. (They will
also upgrade to HTTPS on aliased.example.) Non-HTTPSSVC-aware
clients will just ignore the new record.
Similar to CNAME, HTTPSSVC has no impact on the origin name. When
connecting, clients will continue to treat the authoritative origins
as "https://www.aliased.example" and "https://aliased.example",
respectively, and will validate TLS server certificates accordingly.
1.3. Example: Parameter binding
Suppose that svc.example's default server pool supports HTTP/2, and
it has deployed HTTP/3 on a new server pool with a different
configuration. This can be expressed in the following form:
$ORIGIN svc.example. ; A hosting provider.
pool 7200 IN HTTPSSVC 1 h3pool alpn=h2,h3 esniconfig="123..."
HTTPSSVC 2 . alpn=h2 esniconfig="abc..."
pool 300 IN A 192.0.2.2
AAAA 2001:db8::2
h3pool 300 IN A 192.0.2.3
AAAA 2001:db8::3
This configuration is entirely compatible with the "Apex aliasing"
example, whether the client supports HTTPSSVC or not. If the client
does support HTTPSSVC, all connections will be upgraded to HTTPS, 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, ESNI
configuration, etc.
1.4. Example: Non-HTTPS uses
For services other than HTTPS, the SVCB RR and an [Attrleaf] label
will be used. For example, to reach an example resource of
"baz://api.example.com:8765", the following Alias Form SVCB record
would be used to delegate to "svc4-baz.example.net." which in-turn
could return AAAA/A records and/or SVCB records in ServiceForm.
_8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
HTTPSSVC records use similar [Attrleaf] labels if the origin contains
a non-default port.
1.5. Goals of the SVCB RR
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:
o Provides service endpoints authoritative for the service, along * Provides service endpoints authoritative for the service, along
with parameters associated with each of these endpoints. with parameters associated with each of these endpoints.
o Does not assume that all alternative service endpoints have the * Does not assume that all alternative service endpoints have the
same parameters or capabilities, or are even operated by the same 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 RRs for the same name. For example, if together multiple RRs 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 CDNs or hosting environments, successive queries for that
name may return records that correspond to different environments. name may return records that correspond to different environments.
o 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 delegation of operational authority for an origin within the DNS
to an alternate name. to an alternate name.
Additional goals specific to HTTPSSVC and the HTTPS use-case include: Additional goals specific to HTTPSSVC and the HTTPS use-case include:
o Connect directly to [HTTP3] (QUIC transport) alternative service * Connect directly to [HTTP3] (QUIC transport) alternative service
endpoints endpoints
o Obtain the [ESNI] keys associated with an alternative service * Obtain the [ECH] keys associated with an alternative service
endpoint endpoint
o Support non-default TCP and UDP ports * Support non-default TCP and UDP ports
o Address a set of long-standing issues due to HTTP(S) clients not * Address a set of long-standing issues due to HTTP(S) clients not
implementing support for SRV records, as well as due to a implementing support for SRV records, as well as due to a
limitation that a DNS name can not have both CNAME and NS RRs (as limitation that a DNS name can not have both CNAME and NS RRs (as
is the case for zone apex names) is the case for zone apex names)
o Provide an HSTS-like indication signaling for the duration of the * Provide an HSTS-like indication signaling for the duration of the
DNS RR TTL that the HTTPS scheme should be used instead of HTTP DNS RR TTL that the HTTPS scheme should be used instead of HTTP
(see Section 7.4). (see Section 7.5).
1.6. Overview of the SVCB RR 1.2. Overview of the SVCB RR
This subsection briefly describes the SVCB RR in a non-normative This subsection briefly describes the SVCB RR in a non-normative
manner. (As mentioned above, this all applies equally to the manner. (As mentioned above, this all applies equally to the
HTTPSSVC RR which shares the same encoding, format, and high-level HTTPSSVC RR which shares the same encoding, format, and high-level
semantics.) semantics.)
The SVCB RR has two forms: AliasForm, which aliases a name to another The SVCB RR has two forms: AliasForm, which aliases a name to another
name, and ServiceForm, which provides connection information bound to name, and ServiceForm, which provides connection information bound to
a service endpoint domain. Placing both forms in a single RR type a service endpoint domain. Placing both forms in a single RR type
allows clients to fetch the relevant information with a single query. allows clients to fetch the relevant information with a single query.
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extensible data model for describing network endpoints that are extensible data model for describing network endpoints that are
authoritative for the origin, along with parameters associated with authoritative for the origin, along with parameters associated with
each of these endpoints. each of these endpoints.
For the HTTPS use-case, the HTTPSSVC RR enables many of the benefits For the HTTPS use-case, the HTTPSSVC RR enables many of the benefits
of [AltSvc] without waiting for a full HTTP connection initiation of [AltSvc] without waiting for a full HTTP connection initiation
(multiple roundtrips) before learning of the preferred alternative, (multiple roundtrips) before learning of the preferred alternative,
and without necessarily revealing the user's intended destination to and without necessarily revealing the user's intended destination to
all entities along the network path. all entities along the network path.
1.7. Parameter for ESNI 1.3. Parameter for Encrypted ClientHello
This document also defines a parameter for Encrypted SNI [ESNI] keys. This document also defines a parameter for Encrypted ClientHello
See Section 8. [ECH] keys. See Section 8.
1.8. Terminology 1.4. Terminology
For consistency with [AltSvc], we adopt the following definitions: For consistency with [AltSvc], we adopt the following definitions:
o An "origin" is an information source as in [RFC6454]. For * An "origin" is an information source as in [RFC6454]. For
services other than HTTPS, the exact definition will need to be services other than HTTPS, the exact definition will need to be
provided by the document mapping that service onto the SVCB RR. provided by the document mapping that service onto the SVCB RR.
o The "origin server" is the server that the client would reach when * The "origin server" is the server that the client would reach when
accessing the origin in the absence of the SVCB record or an HTTPS accessing the origin in the absence of the SVCB record or an HTTPS
Alt-Svc. Alt-Svc.
o An "alternative service" is a different server that can serve the * An "alternative service" is a different server that can serve the
origin over a specified protocol. origin over a specified protocol.
For example within HTTPS, the origin consists of a scheme (typically For example within HTTPS, the origin consists of a scheme (typically
"https"), a host name, and a port (typically "443"). "https"), a hostname, and a port (typically "443").
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". HTTPSSVC is a SVCB is a contraction of "service binding". HTTPSSVC is a
contraction of "HTTPS service". SVCB, HTTPSSVC, and future RR types contraction of "HTTPS service". SVCB, HTTPSSVC, and future RR types
that share SVCB's format and registry are collectively known as SVCB- that share SVCB's format and registry are collectively known as SVCB-
compatible RR types. compatible RR types.
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
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records is specified in Section 3. records is specified in Section 3.
2.1. Presentation format 2.1. Presentation format
The presentation format of the record is: The presentation format of the record is:
Name TTL IN SVCB SvcFieldPriority SvcDomainName SvcFieldValue Name TTL IN SVCB SvcFieldPriority SvcDomainName SvcFieldValue
The SVCB record is defined specifically within the Internet ("IN") The SVCB record is defined specifically within the Internet ("IN")
Class ([RFC1035]). SvcFieldPriority is a number in the range Class ([RFC1035]). SvcFieldPriority is a number in the range
0-65535, SvcDomainName is a domain name, and SvcFieldValue is a set 0-65535, SvcDomainName is a domain name (absolute or relative), and
of key=value pairs present for the ServiceForm. Each key SHALL SvcFieldValue is a set of key=value pairs present for the
appear at most once in a SvcFieldValue. The SvcFieldValue is empty ServiceForm. Each key SHALL appear at most once in an SvcFieldValue.
for the AliasForm. The SvcFieldValue is empty for the AliasForm.
2.1.1. Presentation format for SvcFieldValue key=value pairs 2.1.1. Presentation format for SvcFieldValue key=value pairs
In ServiceForm, the SvcFieldValue consists of zero or more elements In ServiceForm, the SvcFieldValue consists of zero or more elements
separated by whitespace. Each element represents a key=value pair. separated by whitespace. Each element represents a key=value pair.
Keys are IANA-registered SvcParamKeys (Section 11.1) with both a Keys are IANA-registered SvcParamKeys (Section 12.1) with both a
case-insensitive string representation and a numeric representation case-insensitive string representation and a numeric representation
in the range 0-65535. Registered key names should only contain in the range 0-65535. Registered key names should only contain
characters from the ranges "a"-"z", "0"-"9", and "-". In ABNF characters from the ranges "a"-"z", "0"-"9", and "-". In ABNF
[RFC5234], [RFC5234],
ALPHA-LC = %x61-7A ; a-z
ALPHA_LC = %x61-7A ; a-z key = 1*(ALPHA-LC / DIGIT / "-")
key = ALPHA_LC / DIGIT / "-" display-key = 1*(ALPHA / DIGIT / "-")
display-key = ALPHA / DIGIT / "-"
Values are in a format specific to the SvcParamKey. Their definition Values are in a format specific to the SvcParamKey. Their definition
should specify both their presentation format and wire encoding should specify both their presentation format and wire encoding
(e.g., domain names, binary data, or numeric values). (e.g., domain names, binary data, or numeric values). The initial
keys and formats are defined in Section 6.
The presentation format for SvcFieldValue is a whitespace-separated The presentation format for SvcFieldValue is a whitespace-separated
list of elements representing a key-value pair, with an absent value list of key=value pairs. When the value is omitted, or both the
or "=" indicating an empty value. Each element is presented in the value and the "=" are omitted, the presentation value is the empty
following form: string.
; basic-visible is VCHAR minus DQUOTE, ";", and "\" ; basic-visible is VCHAR minus DQUOTE, ";", "(", ")", and "\".
basic-visible = %x21 / %x23-3A / %x3C-5B / %x5D-7E basic-visible = %x21 / %x23-27 / %2A-3A / %x3C-5B / %x5D-7E
escaped-char = "\" (VCHAR / WSP) escaped-char = "\" (VCHAR / WSP)
contiguous = *(basic-visible / escaped-char) contiguous = 1*(basic-visible / escaped-char)
quoted-string = DQUOTE *(contiguous / WSP) DQUOTE quoted-string = DQUOTE *(contiguous / WSP) DQUOTE
value = quoted-string / contiguous value = quoted-string / contiguous
pair = display-key "=" value pair = display-key "=" value
element = display-key / pair element = display-key / pair
The value format is intended to match the definition of <character- The value format is intended to match the definition of <character-
string> in [RFC1035] Section 5.1. (Unlike <character-string>, the string> in [RFC1035] Section 5.1. (Unlike <character-string>, the
length of a value is not limited to 255 characters.) length of a value is not limited to 255 characters.)
Unrecognized keys are represented in presentation format as Unrecognized keys are represented in presentation format as
"keyNNNNN" where NNNNN is the numeric value of the key type without "keyNNNNN" where NNNNN is the numeric value of the key type without
leading zeros. In presentation format, values of unrecognized keys leading zeros. In presentation format, values corresponding to
SHALL be represented in wire format, using decimal escape codes (e.g. unrecognized keys SHALL be represented in wire format, using decimal
\255) when necessary. escape codes (e.g. \255) when necessary.
Elements in presentation format MAY appear in any order. When decoding values of unrecognized keys in the presentation format:
* a character other than "\" represents its ASCII value in wire
format.
* the character "\" followed by three decimal digits, up to 255,
represents an octet in the wire format.
* the character "\" followed by any allowed character, except a
decimal digit, represents the subsequent character's ASCII value.
Elements in presentation format MAY appear in any order, but keys
MUST NOT be repeated.
2.2. SVCB RDATA Wire Format 2.2. SVCB RDATA Wire Format
The RDATA for the SVCB RR consists of: The RDATA for the SVCB RR consists of:
o a 2 octet field for SvcFieldPriority as an integer in network byte * a 2 octet field for SvcFieldPriority as an integer in network byte
order. order.
o the uncompressed, fully-qualified SvcDomainName, represented as a * the uncompressed, fully-qualified SvcDomainName, represented as a
sequence of length-prefixed labels as in Section 3.1 of [RFC1035]. sequence of length-prefixed labels as in Section 3.1 of [RFC1035].
o the SvcFieldValue byte string, consuming the remainder of the * the SvcFieldValue byte string, consuming the remainder of the
record (so smaller than 65535 octets and constrained by the RDATA record (so smaller than 65535 octets and constrained by the RDATA
and DNS message sizes). and DNS message sizes).
AliasForm is defined by SvcFieldPriority being 0. AliasForm is defined by SvcFieldPriority being 0.
When SvcFieldValue is non-empty (ServiceForm), it contains a series When SvcFieldValue is non-empty (ServiceForm), it contains a series
of SvcParamKey=SvcParamValue pairs, represented as: of SvcParamKey=SvcParamValue pairs, represented as:
o 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. network byte order. (See Section 12.1.2 for the defined values.)
o a 2 octet field containing the length of the SvcParamValue as an * a 2 octet field containing the length of the SvcParamValue as an
integer between 0 and 65535 in network byte order (but constrained integer between 0 and 65535 in network byte order (but constrained
by the RDATA and DNS message sizes). by the RDATA and DNS message sizes).
o an octet string of the length defined by the previous field. * an octet string of this length whose contents are 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
o the parser reaches the end of the RDATA while parsing a * the parser reaches the end of the RDATA while parsing an
SvcFieldValue. SvcFieldValue.
o SvcParamKeys are not in strictly increasing numeric order. * SvcParamKeys are not in strictly increasing numeric order.
o a SvcParamValue for a known SvcParamKey does not have the expected * the SvcParamValue for an 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.
TODO: decide if we want special handling for any SvcParamKey ranges? TODO: decide if we want special handling for any SvcParamKey ranges?
For example: range for greasing; experimental range; range-of- For example: range for greasing; experimental range; range-of-
mandatory-to-use-the-RR vs range of ignore-just-param-if-unknown. mandatory-to-use-the-RR vs range of ignore-just-param-if-unknown.
2.3. SVCB owner names 2.3. SVCB owner names
When querying the SVCB RR, an origin is typically translated into a When querying the SVCB RR, an origin is translated into a QNAME by
QNAME by prefixing the port and scheme with "_", then concatenating prepending the hostname with a label indicating the scheme, prefixed
them with the host name, resulting in a domain name like with an underscore, resulting in a domain name like
"_8004._examplescheme.api.example.com.". "_examplescheme.api.example.com.".
Protocol mappings for SVCB MAY remove the port or replace it with Protocol mapping documents MAY specify additional underscore-prefixed
other protocol-specific information, but MUST retain the scheme in labels to be prepended. For schemes that specify a port
the QNAME. RR types other than SVCB can define additional behavior (Section 3.2.3 of [URI]), one reasonable possibility is to prepend
for translating origins to QNAMEs. See Section 7.1 for the HTTPSSVC the indicated port number (or the default if no port number is
behavior. specified). We term this behavior "Port Prefix Naming", and use it
in the examples throughout this document.
See Section 7.1 for the HTTPSSVC behavior.
When a prior CNAME or SVCB record has aliased to an SVCB record, each When a prior CNAME or SVCB record has aliased to an SVCB record, each
RR shall be returned under its own owner name. RR shall be returned under its own owner name.
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, clients MUST continue to validate validation purposes. For example, clients MUST continue to validate
TLS certificate hostnames based on the origin host. TLS certificate hostnames based on the origin host.
As an example: 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
"svc4.example.net". The owner of example.net, in turn, 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" esniconfig="..." ) alpn="bar" port="8004" echconfig="..." )
would indicate that "foo://api.example.com:8443" is aliased to the to indicate that these services are served on port number 8004, which
service endpoints offered at "svc4.example.net" on port number 8004, supports the protocol "bar" and its associated transport in addition
which support the protocol "bar" and its associated transport in to the default transport protocol for "foo://".
addition to the default transport protocol for "foo://".
(Parentheses are used to ignore a line break ([RFC1035] (Parentheses are used to ignore a line break ([RFC1035]
Section 5.1).) Section 5.1).)
2.4. SvcRecordType 2.4. SvcRecordType
The SvcRecordType is indicated by the SvcFieldPriority, and defines The SvcRecordType is indicated by the SvcFieldPriority, and defines
the form of the SVCB RR. When SvcFieldPriority is 0, the SVCB the form of the SVCB RR. When SvcFieldPriority is 0, the SVCB
SvcRecordType is defined to be in AliasForm. Otherwise, the SVCB SvcRecordType is defined to be in AliasForm. Otherwise, the SVCB
SvcRecordType is defined to be in ServiceForm. SvcRecordType is defined to be in ServiceForm.
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are present, clients or recursive resolvers SHOULD pick one at are present, clients or recursive resolvers SHOULD pick one at
random. random.
The AliasForm's primary purpose is to allow aliasing at the zone The AliasForm's primary purpose is to allow aliasing at the zone
apex, where CNAME is not allowed. For example, if an operator of apex, where CNAME is not allowed. For example, if an operator of
https://example.com wanted to point HTTPS requests to a service https://example.com wanted to point HTTPS requests to a service
operating at svc.example.net, they would publish a record such as: operating at svc.example.net, they would publish a record such as:
example.com. 3600 IN SVCB 0 svc.example.net. example.com. 3600 IN SVCB 0 svc.example.net.
The SvcDomainName MUST point to a domain name that contains another In AliasForm, SvcDomainName MUST be the name of a domain that has
SVCB record, address (AAAA and/or A) records, or both address records SVCB, AAAA, or A records. It MUST NOT be equal to the owner name, as
and a ServiceForm SVCB record. this would cause a loop.
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 SvcDomainName MAY be the owner of a CNAME CNAME record, and the SvcDomainName MAY be the owner of a CNAME
record. Clients and recursive resolvers MUST follow CNAMEs as record. Clients and recursive resolvers MUST follow CNAMEs as
normal. normal.
Due to the risk of loops, clients and recursive resolvers MUST To avoid unbounded alias chains, clients and recursive resolvers MUST
implement loop detection. Chains of consecutive SVCB and CNAME impose a limit on the total number of SVCB aliases they will follow
records SHOULD be limited to (8?) prior to reaching terminal address for each resolution request. This limit MUST NOT be zero, i.e.
records. implementations MUST be able to follow at least one AliasForm record.
The exact value of this limit is left to implementations.
For compatibility and performance, zone owners SHOULD NOT configure
their zones to require following multiple AliasForm records.
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.
Note that SVCB AliasForm RRs do not alias to RR types other than Note that SVCB AliasForm RRs do not alias to RR types other than
address records (AAAA and A), CNAMEs, and ServiceForm SVCB records. address records (AAAA and A), CNAMEs, and ServiceForm SVCB records.
For example, an AliasForm SVCB record does not alias to an HTTPSSVC For example, an AliasForm SVCB record does not alias to an HTTPSSVC
record, nor vice-versa. record, nor vice-versa.
2.6. SVCB records: ServiceForm 2.6. SVCB records: ServiceForm
When SvcRecordType is the ServiceForm, the combination of When SvcRecordType is the ServiceForm, the combination of
SvcDomainName and SvcFieldValue parameters within each resource SvcDomainName and SvcFieldValue parameters within each resource
record associates an alternative service location with its connection record associates an alternative service location with its connection
parameters. parameters.
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record associates an alternative service location with its connection record associates an alternative service location with its 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 SvcFieldValues are applied for connections of that that explains how SvcFieldValues 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 SvcFieldValue parameters that they do not recognize. MUST ignore SvcFieldValue parameters that they do not recognize.
2.6.1. Special handling of "." for SvcDomainName in ServiceForm 2.6.1. Special handling of "." for SvcDomainName in ServiceForm
For ServiceForm SVCB RRs, if SvcDomainName has the value ".", then For ServiceForm SVCB RRs, if SvcDomainName has the value "."
the owner name of this record MUST be used as the effective (represented in the wire format as a zero-length label), then the
SvcDomainName. (The SvcDomainName of an SVCB RR in AliasForm MUST owner name of this record MUST be used as the effective
NOT have this value.) SvcDomainName.
For example, in the following example "svc2.example.net" is the For example, in the following example "svc2.example.net" is the
effective SvcDomainName: effective SvcDomainName:
www.example.com. 7200 IN HTTPSSVC svc.example.net. www.example.com. 7200 IN HTTPSSVC 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 HTTPSSVC 1 . port=8002 esniconfig="..." svc2.example.net. 7200 IN HTTPSSVC 1 . port=8002 echconfig="..."
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
2.6.2. SvcFieldPriority 2.6.2. SvcFieldPriority
As RRs within an RRSet are explicitly unordered collections, the As RRs within an RRSet are explicitly unordered collections, the
SvcFieldPriority value serves to indicate priority. SVCB RRs with a SvcFieldPriority value serves to indicate priority. SVCB RRs with a
smaller SvcFieldPriority value SHOULD be given preference over RRs smaller SvcFieldPriority value SHOULD be given preference over RRs
with a larger SvcFieldPriority value. with a larger SvcFieldPriority value.
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An SVCB-aware client resolves an origin HOST by attempting to An SVCB-aware client resolves an origin HOST by attempting to
determine the preferred SvcFieldValue and IP addresses for its determine the preferred SvcFieldValue and IP addresses for its
service, using the following procedure: service, using the following procedure:
1. Issue parallel AAAA/A and SVCB queries for the name HOST. The 1. Issue parallel AAAA/A and SVCB queries for the name HOST. The
answers for these may or may not include CNAME pointers before answers for these may or may not include CNAME pointers before
reaching one or more of these records. reaching one or more of these records.
2. If an SVCB record of AliasForm SvcRecordType is returned for 2. If an SVCB record of AliasForm SvcRecordType is returned for
HOST, clients MUST loop back to step 1 replacing HOST with HOST, clients MUST loop back to step 1 replacing HOST with
SvcDomainName, subject to loop detection heuristics. SvcDomainName, subject to chain length limits and loop detection
heuristics (see Section 3.1).
3. If one or more SVCB records of ServiceForm SvcRecordType are 3. If one or more SVCB records of ServiceForm SvcRecordType are
returned for HOST, clients should select the highest-priority returned for HOST, clients should select the highest-priority
option with acceptable parameters, and resolve AAAA and/or A option with acceptable parameters, and resolve AAAA and/or A
records for its SvcDomainName if they are not already available. records for its SvcDomainName if they are not already available.
These are the preferred SvcFieldValue and IP addresses. If the These are the preferred SvcFieldValue and IP addresses. If the
connection fails, the client MAY try to connect using values from connection fails, the client MAY try to connect using values from
a lower-priority record. If none of the options succeed, the a lower-priority record. If none of the options succeed, the
client SHOULD connect to the origin server directly. client SHOULD connect to the origin server directly.
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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
responses, based on their size or other observable patterns. responses, based on their size or other observable patterns.
Similarly, if the client enforces DNSSEC validation on A/AAAA Similarly, if the client enforces DNSSEC validation on A/AAAA
responses, it MUST NOT fall back to non-SVCB connection establishment responses, it MUST NOT fall back to non-SVCB connection establishment
if the SVCB response fails to validate. if the SVCB response fails to validate.
If the client is unable to complete SVCB resolution due to its chain
length limit, the client SHOULD fall back to non-SVCB connection, as
if the origin'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]) SHOULD disable SVCB ([RFC7231] Section 4.3.6) or SOCKS5 ([RFC1928]) SHOULD disable SVCB
support if performing SVCB queries would violate the client's privacy support if performing SVCB queries would violate the client's privacy
intent. intent.
If the client can safely perform SVCB queries (e.g. via the proxy or If the client can safely perform SVCB queries (e.g. via the proxy or
an affiliated resolver), the client SHOULD follow the standard SVCB an affiliated resolver), the client SHOULD follow the standard SVCB
resolution process, selecting the highest priority option that is resolution process, selecting the highest priority option that is
compatible with the client and the proxy. The client SHOULD provide compatible with the client and the proxy. The client SHOULD provide
the final SvcDomainName and port (if present) to the proxy as the the final SvcDomainName and port to the proxy, which will perform any
destination host and port. required A and AAAA lookups.
Providing the proxy with the final SvcDomainName has several Providing the proxy with the final SvcDomainName has several
benefits: benefits:
o It allows the client to use the SvcFieldValue, if present, which * It allows the client to use the SvcFieldValue, if present, which
is only usable with a specific SvcDomainName. The SvcFieldValue is only usable with a specific SvcDomainName. The SvcFieldValue
may include information that enhances performance (e.g. alpn) and may include information that enhances performance (e.g. alpn) and
privacy (e.g. esniconfig). privacy (e.g. echconfig).
o It allows the origin to delegate the apex domain. * It allows the origin to delegate the apex domain.
o It allows the proxy to select between IPv4 and IPv6 addresses for * It allows the proxy to select between IPv4 and IPv6 addresses for
the server according to its configuration, and receive addresses the server according to its configuration, and receive addresses
based on its network geolocation. based on its network geolocation.
4. DNS Server Behavior 4. DNS Server Behavior
4.1. Authoritative servers 4.1. Authoritative servers
When replying to an SVCB query, authoritative DNS servers SHOULD When replying to an SVCB query, authoritative DNS servers SHOULD
return A, AAAA, and SVCB records (as well as any relevant CNAME or return A, AAAA, and SVCB records (as well as any relevant CNAME or
[DNAME] records) in the Additional Section for any in-bailiwick [DNAME] records) in the Additional Section for any in-bailiwick
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unknown RR type resolution under [RFC3597]). For followup unknown RR type resolution under [RFC3597]). For followup
resolutions performed during this procedure, we define incorporation resolutions performed during this procedure, we define incorporation
as adding all Answer and Additional RRs to the Additional section, as adding all Answer and Additional RRs to the Additional section,
and all Authority RRs to the Authority section, without altering the and all Authority RRs to the Authority section, without altering the
response code. response code.
Upon receiving an SVCB query, recursive resolvers SHOULD start with Upon receiving an SVCB query, recursive resolvers SHOULD start with
the standard resolution procedure, and then follow this procedure to the standard resolution procedure, and then follow this procedure to
construct the full response to the stub resolver: construct the full response to the stub resolver:
1. Incorporate the results of SVCB resolution. 1. Incorporate the results of SVCB resolution. If the chain length
limit has been reached, terminate successfully (i.e. a NOERROR
response).
2. If any of the resolved SVCB records are in AliasForm, choose an 2. If any of the resolved SVCB records are in AliasForm, choose an
AliasForm record at random, and resolve SVCB, A, and AAAA records AliasForm record at random, and resolve SVCB, A, and AAAA records
for its SvcDomainName. for its SvcDomainName.
* If any SVCB records are resolved, go to step 1, subject to * If any SVCB records are resolved, go to step 1.
loop detection heuristics.
* 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 ServiceForm. Resolve A and 3. All the resolved SVCB records are in ServiceForm. Resolve A and
AAAA queries for each SvcDomainName (or for the owner name if AAAA queries for each SvcDomainName (or for the owner name if
SvcDomainName is "."), incorporate all the results, and SvcDomainName is "."), incorporate all the results, and
terminate. 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]). follow (e.g. CNAME, [DNAME]).
4.3. General requirements 4.3. General requirements
All DNS servers SHOULD treat the SvcParam portion of the SVCB RR as All DNS servers SHOULD treat the SvcFieldValue portion of the SVCB RR
opaque and SHOULD NOT try to alter their behavior based on its as opaque and SHOULD NOT try to alter their behavior based on its
contents. contents.
When responding to a query that includes the DNSSEC OK bit When responding to a query that includes the DNSSEC OK bit
([RFC3225]), DNSSEC-capable recursive and authoritative DNS servers ([RFC3225]), DNSSEC-capable recursive and authoritative DNS servers
MUST accompany each RRSet in the Additional section with the same MUST accompany each RRSet in the Additional section with the same
DNSSEC-related records that they would send when providing that RRSet DNSSEC-related records that they would send when providing that RRSet
as an Answer (e.g. RRSIG, NSEC, NSEC3). as an Answer (e.g. RRSIG, NSEC, NSEC3).
5. Performance optimizations 5. Performance optimizations
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before performing any followup queries. With these optimizations in before performing any followup queries. With these optimizations in
place, and conforming DNS servers, using SVCB does not add network place, and conforming DNS servers, using SVCB does not add network
latency to connection setup. latency to connection setup.
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, a TLS altered by the SVCB response until it arrives. For example, a TLS
ClientHello can be altered by the "esniconfig" value of an SVCB ClientHello can be altered by the "echconfig" value of an SVCB
response (Section 6.3). Clients implementing this optimization response (Section 6.3). Clients implementing this optimization
SHOULD wait for 50 milliseconds before starting optimistic pre- SHOULD wait for 50 milliseconds before starting optimistic pre-
connection, as per the guidance in [HappyEyeballsV2]. connection, as per the guidance in [HappyEyeballsV2].
An SVCB record is consistent with a connection if the client would An 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
an SVCB record is consistent with an active or in-progress connection an 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 (
esniconfig="111..." ipv6hint=2001:db8::1 port=1234 ... ) echconfig="111..." ipv6hint=2001:db8::1 port=1234 ... )
SVCB 2 svc2.example.net ( SVCB 2 svc2.example.net (
esniconfig="222..." ipv6hint=2001:db8::2 port=1234 ... ) echconfig="222..." 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 "[2001:db8::2]:1234", it MAY proceed with TLS on that connection
using "esniconfig="222..."", even though the other record in the using "echconfig="222..."", even though the other record in the RRSet
RRSet has higher priority. 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 must proceed as described in Step 3 of progress connection, clients must proceed as described in Step 3 of
the procedure in Section 3. the procedure 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 might be appropriate when the maximum the associated RRSets. This is REQUIRED when the chain length limit
response size is reached, or when responding before fully chasing is reached (Section 4.2 step 1), but might also be appropriate when
dependencies would improve performance. When omitting certain the maximum response size is reached, or when responding before fully
RRSets, recursive resolvers SHOULD prioritize information from higher chasing dependencies would improve performance. When omitting
priority ServiceForm records over lower priority ServiceForm records. certain RRSets, recursive resolvers SHOULD prioritize information
from higher priority ServiceForm records over lower priority
ServiceForm records.
As discussed in Section 3, clients MUST be able fetch additional As discussed in Section 3, clients MUST be able to fetch additional
information that is required to use an SVCB record, if it is not information that is required to use an 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.
5.3. Structuring zones for performance 5.3. Structuring zones for performance
To avoid a delay for clients using a nonconforming recursive To avoid a delay for clients using a nonconforming recursive
resolver, domain owners SHOULD use a single SVCB record whose resolver, domain owners SHOULD use a single SVCB record whose
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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*255(OCTET) alpn-id = 1*255(OCTET)
The presentation value of "alpn" is a comma-separated list of one or The presentation value of "alpn" is a comma-separated list of one or
more "alpn-id"s. Any commas present in the protocol-id are escaped more "alpn-id"s. Any commas present in the protocol-id are escaped
by a backslash: by a backslash:
escaped-octet = %x00-2b / "\," / %x2d-5b / "\\" / %5d-%FF escaped-octet = %x00-2b / "\," / %x2d-5b / "\\" / %x5D-FF
escaped-id = 1*255(escaped-octet) escaped-id = 1*(escaped-octet)
alpn-value = escaped-id *("," escaped-id) alpn-value = escaped-id *("," escaped-id)
In the wire format for "alpn", each ALPN identifier ("alpn-id") is The wire format value for "alpn" consists of at least one ALPN
prefixed by its length as a single octet, and these length-value identifier ("alpn-id") prefixed by its length as a single octet, and
pairs are concatenated to form the SvcParamValue. These pairs MUST these length-value pairs are concatenated to form the SvcParamValue.
exactly fill the SvcParamValue; otherwise, the SvcParamValue is These pairs MUST exactly fill the SvcParamValue; otherwise, the
malformed. SvcParamValue is 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. be empty.
Each scheme that uses this SvcParamKey defines a "default set" of Each scheme that uses this SvcParamKey defines a "default set" of
supported ALPNs, which SHOULD NOT be empty. To determine the set of supported ALPNs, which SHOULD NOT be empty. To determine the set of
protocol suites supported by an endpoint (the "ALPN set"), the client protocol suites supported by an endpoint (the "ALPN set"), the client
parses the set of ALPN identifiers in the "alpn" parameter, and then parses the set of ALPN identifiers in the "alpn" parameter, and then
adds the default set unless the "no-default-alpn" SvcParamKey is adds the default set unless the "no-default-alpn" SvcParamKey is
present. The presence of a value in the alpn set indicates that this present. The presence of a value in the alpn set indicates that this
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Once the client has formulated the ClientHello, protocol negotiation Once the client has formulated the ClientHello, protocol negotiation
on that connection proceeds as specified in [ALPN], without regard to on that connection proceeds as specified in [ALPN], without regard to
the SVCB ALPN set. To preserve the security guarantees of this the SVCB ALPN set. To preserve the security guarantees of this
process, clients MUST consolidate all compatible ALPN IDs into a process, clients MUST consolidate all compatible ALPN IDs into a
single ProtocolNameList. single ProtocolNameList.
6.2. "port" 6.2. "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 contact this alternative service. used to contact this alternative service. If this key is not
present, clients SHALL use the origin server's port number.
The presentation format of the SvcParamValue is a numeric value The presentation format of the SvcParamValue is a numeric value
between 0 and 65535 inclusive. Any other values (e.g. the empty between 0 and 65535 inclusive. Any other values (e.g. the empty
value) are syntax errors. value) are syntax errors.
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.
6.3. "esniconfig" If a port-restricting firewall is in place between some client and
the service endpoint, changing the port number might cause that
client to lose access to the service, so operators should exercise
caution when using this SvcParamKey to specify a non-default port.
The SvcParamKey for ESNI is "esniconfig". Its value is defined in 6.3. "echconfig"
Section 8. It is applicable to most TLS-based protocols.
When publishing a record containing an "esniconfig" parameter, the The SvcParamKey to enable Encrypted ClientHello (ECH) is "echconfig".
Its value is defined in Section 8. It is applicable to most TLS-
based protocols.
When publishing a record containing an "echconfig" parameter, the
publisher MUST ensure that all IP addresses of SvcDomainName publisher MUST ensure that all IP addresses of SvcDomainName
correspond to servers that have access to the corresponding private correspond to servers that have access to the corresponding private
key or are authoritative for the fallback domain. (See [ESNI] for key or are authoritative for the public name. (See Section 7.2.2 of
more details about the fallback domain.) This yields an anonymity [ECH] for more details about the public name.) This yields an
set of cardinality equal to the number of ESNI-enabled server domains anonymity set of cardinality equal to the number of ECH-enabled
supported by a given client-facing server. Thus, even with SNI server domains supported by a given client-facing server. Thus, even
encryption, an attacker who can enumerate the set of ESNI-enabled with an encrypted ClientHello, an attacker who can enumerate the set
domains supported by a client-facing server can guess the correct SNI of ECH-enabled domains supported by a client-facing server can guess
with probability at least 1/K, where K is the size of this ESNI- the correct SNI with probability at least 1/K, where K is the size of
enabled server anonymity set. This probability may be increased via this ECH-enabled server anonymity set. This probability may be
traffic analysis or other mechanisms. increased via traffic analysis or other mechanisms.
6.4. "ipv4hint" and "ipv6hint" 6.4. "ipv4hint" and "ipv6hint"
The "ipv4hint" and "ipv6hint" keys represent IP address hints for the The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
service. If A and AAAA records for SvcDomainName are locally MAY use to reach the service. If A and AAAA records for
available, the client SHOULD ignore these hints. Otherwise, clients SvcDomainName are locally available, the client SHOULD ignore these
SHOULD perform A and/or AAAA queries for SvcDomainName as in hints. Otherwise, clients SHOULD perform A and/or AAAA queries for
Section 3, and clients SHOULD use the IP address in those responses SvcDomainName as in Section 3, and clients SHOULD use the IP address
for future connections. Clients MAY opt to terminate any connections in those responses for future connections. Clients MAY opt to
using the addresses in hints and instead switch to the addresses in terminate any connections using the addresses in hints and instead
response to the SvcDomainName. Failure to use A and/or AAAA response switch to the addresses in response to the SvcDomainName query.
addresses may negatively impact load balancing or other geo-aware Failure to use A and/or AAAA response addresses could negatively
features and thereby degrade client performance. impact load balancing or other geo-aware features and thereby degrade
client performance.
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. Like an A or AAAA RRSet, the list of addresses network byte order. Like an A or AAAA RRSet, the list of addresses
represents an unordered collection, and clients SHOULD pick addresses represents an unordered collection, and clients SHOULD pick addresses
to use in a random order. An empty list of addresses is invalid. to use in a random order. An empty 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 [HappyEyeballsV2]. When only "ipv4hint" is use an approach such as [HappyEyeballsV2]. When only "ipv4hint" is
present, IPv6-only clients may synthesize IPv6 addresses as specified present, IPv6-only clients may synthesize IPv6 addresses as specified
in [RFC7050] or ignore the "ipv4hint" key and wait for AAAA in [RFC7050] or ignore the "ipv4hint" key and wait for AAAA
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The HTTPSSVC wire format and presentation format are identical to The HTTPSSVC wire format and presentation format are identical to
SVCB, and both share the SvcParamKey registry. SVCB semantics apply SVCB, and both share the SvcParamKey registry. SVCB semantics apply
equally to HTTPSSVC unless specified otherwise. equally to HTTPSSVC unless specified otherwise.
All the SvcParamKeys defined in Section 6 are permitted for use in All the SvcParamKeys defined in Section 6 are permitted for use in
HTTPSSVC. The default set of ALPN IDs is the single value HTTPSSVC. The default set of ALPN IDs is the single value
"http/1.1". "http/1.1".
The presence of an HTTPSSVC record for an origin also indicates that The presence of an HTTPSSVC record for an origin also indicates that
all HTTP resources are available over HTTPS, as discussed in all HTTP resources are available over HTTPS, as discussed in
Section 7.4. This allows HTTPSSVC RRs to apply to pre-existing Section 7.5. This allows HTTPSSVC RRs to apply to pre-existing
"http" scheme URLs, while ensuring that the client uses a secure and "http" scheme URLs, while ensuring that the client uses a secure and
authenticated HTTPS connection. authenticated HTTPS connection.
The HTTPSSVC RR parallels the concepts introduced in the HTTP The HTTPSSVC RR parallels the concepts introduced in the HTTP
Alternative Services proposed standard [AltSvc]. Clients and servers Alternative Services proposed standard [AltSvc]. Clients and servers
that implement HTTPSSVC are NOT REQUIRED to implement Alt-Svc. that implement HTTPSSVC are NOT REQUIRED to implement Alt-Svc.
7.1. Owner names for HTTPSSVC records 7.1. Owner names for HTTPSSVC records
The HTTPSSVC RR extends the behavior for determining a QNAME The HTTPSSVC RR uses Port Prefix Naming (Section 2.3), with one
specified above in Section 2.3. In particular, if the scheme is modification: if the scheme is "https" and the port is 443, then the
"https" with port 443 then the client's original QNAME is equal to client's original QNAME is equal to the origin hostname, without any
the origin host name. prefix labels.
By removing the [Attrleaf] labels used in SVCB, this construction By removing the [Attrleaf] labels used in SVCB, this construction
enables offline DNSSEC signing of wildcard domains, which are enables offline DNSSEC signing of wildcard domains, which are
commonly used with HTTPS. Reusing the origin hostname also allows commonly used with HTTPS. Reusing the origin hostname also allows
the targets of existing CNAME chains (e.g. CDN hosts) to start the targets of existing CNAME chains (e.g. CDN hosts) to start
returning HTTPSSVC responses without requiring origin domains to returning HTTPSSVC responses without requiring origin domains to
configure and maintain an additional delegation. configure and maintain an additional delegation.
For HTTPS origins with ports other than 443, the port and scheme Following of HTTPSSVC AliasForm and CNAME aliases is unchanged from
continue to be prefixed to the hostname as described in Section 2.3. SVCB.
Following of HTTPSSVC AliasForm and CNAME aliases is also unchanged
from SVCB.
Clients always convert "http" URLS to "https" before performing an Clients always convert "http" URLs to "https" before performing an
HTTPSSVC query using the process described in Section 7.4, so domain HTTPSSVC query using the process described in Section 7.5, so domain
owners MUST NOT publish HTTPSSVC records with a prefix of "_http". owners MUST NOT publish HTTPSSVC records 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 host. hostnames based on the origin host.
7.2. Relationship to Alt-Svc 7.2. Relationship to Alt-Svc
Publishing a ServiceForm HTTPSSVC record in DNS is intended to be Publishing a ServiceForm HTTPSSVC record in DNS is intended to be
similar to transmitting an Alt-Svc field value over HTTPS, and similar to transmitting an Alt-Svc field value over HTTPS, and
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configuration. configuration.
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 HTTPSSVC DNS Field Value specifically to the client. When using an HTTPSSVC DNS
record, groups of clients will necessarily receive the same record, groups of clients will necessarily receive the same
SvcFieldValue. Therefore, HTTPSSVC is not suitable for uses that SvcFieldValue. Therefore, HTTPSSVC is not suitable for uses that
require single-client granularity. require single-client granularity.
7.3. Interaction with Alt-Svc 7.3. Interaction with Alt-Svc
Clients that do not implement support for ESNI MAY skip the HTTPSSVC Clients that do not implement support for Encrypted ClientHello MAY
query if a usable Alt-Svc value is available in the local cache. If skip the HTTPSSVC query if a usable Alt-Svc value is available in the
Alt-Svc connection fails, these clients SHOULD fall back to the local cache. If Alt-Svc connection fails, these clients SHOULD fall
HTTPSSVC client connection procedure (Section 3). back to the HTTPSSVC client connection procedure (Section 3).
For clients that implement support for ESNI, the interaction between For clients that implement support for ECH, the interaction between
HTTPSSVC and Alt-Svc is described in Section 8.1. HTTPSSVC and Alt-Svc is described in Section 8.1.
This specification does not alter the DNS queries performed when This specification does not alter the DNS queries performed when
connecting to an Alt-Svc hostname (typically A and/or AAAA only). connecting to an Alt-Svc hostname (typically A and/or AAAA only).
7.4. HTTP Strict Transport Security 7.4. Requiring Server Name Indication
Clients MUST NOT use an HTTPSSVC response unless the client supports
TLS Server Name Indication (SNI) and indicate the origin name when
negotiating TLS. This supports the conservation of IP addresses.
Note that the TLS SNI (and also the HTTP "Host" or ":authority") will
indicate the origin, not the SvcDomainName.
7.5. HTTP Strict Transport Security
By publishing an HTTPSSVC record, the server operator indicates that By publishing an HTTPSSVC record, the server operator indicates that
all useful HTTP resources on that origin are reachable over HTTPS, all useful HTTP resources on that origin are reachable over HTTPS,
similar to HTTP Strict Transport Security [HSTS]. When an HTTPSSVC similar to HTTP Strict Transport Security [HSTS]. When an HTTPSSVC
record is present for an origin, all "http" scheme requests for that record is present for an origin, all "http" scheme requests for that
origin SHOULD logically be redirected to "https". origin SHOULD logically be redirected to "https".
Prior to making an "http" scheme request, the client SHOULD perform a Prior to making an "http" scheme request, the client SHOULD perform a
lookup to determine if an HTTPSSVC record is available for that lookup to determine if any HTTPSSVC records exist for that origin.
origin. To do so, the client SHOULD construct a corresponding To do so, the client SHOULD construct a corresponding "https" URL as
"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], point 5.
If an HTTPSSVC record is present for this "https" URL, the client If an HTTPSSVC query for this "https" URL returns any HTTPSSVC
should treat this as the equivalent of receiving an HTTP "307 records (AliasForm or ServiceForm), the client SHOULD act as if it
Temporary Redirect" redirect to the "https" URL. Because HTTPSSVC is has received an HTTP "307 Temporary Redirect" redirect to this
received over an often insecure channel (DNS), clients MUST NOT place "https" URL. Because HTTPSSVC is received over an often insecure
any more trust in this signal than if they had received a 307 channel (DNS), clients MUST NOT place any more trust in this signal
redirect over cleartext HTTP. than if they had received a 307 redirect over cleartext HTTP.
When making an "https" scheme request to an origin with an HTTPSSVC When making an "https" scheme request to an origin with an HTTPSSVC
record, either directly or via the above redirect, the client SHOULD record, either directly or via the above redirect, the client SHOULD
terminate the connection if there are any errors with the underlying terminate the connection if there are any errors with the underlying
secure transport, such as errors in certificate validation. This secure transport, such as errors in certificate validation. This
aligns with Section 8.4 and Section 12.1 of [HSTS]. aligns with Section 8.4 and Section 12.1 of [HSTS].
8. SVCB/HTTPSSVC parameter for ESNI keys 7.6. HTTP-based protocols
The SVCB "esniconfig" parameter is defined for conveying the ESNI We define an "HTTP-based protocol" as one that involves connecting to
configuration of an alternative service. The value of the parameter an "http:" or "https:" URL. When implementing an HTTP-based
is an ESNIConfig structure [ESNI]. In presentation format, the protocol, clients that use HTTPSSVC for HTTP SHOULD also use it for
structure is encoded in [base64]. The SVCB SvcParamValue wire format this URL. For example, clients that support HTTPSSVC and implement
is the octet string containing the binary ESNIConfig structure. the altered [WebSocket] opening handshake from [FETCH] SHOULD use
HTTPSSVC for the "requestURL".
An HTTP-based protocol MAY define its own SVCB mapping. Such
mappings MAY be defined to take precedence over HTTPSSVC.
8. SVCB/HTTPSSVC parameter for ECH configuration
The SVCB "echconfig" parameter is defined for conveying the ECH
configuration of an alternative service. In wire format, the value
of the parameter is an ECHConfigs vector [ECH], including the
redundant length prefix. In presentation format, the value is
encoded in [base64].
When ECH is in use, the TLS ClientHello is divided into an
unencrypted "outer" and an encrypted "inner" ClientHello. The outer
ClientHello is an implementation detail of ECH, and its contents are
controlled by the ECHConfig in accordance with [ECH]. The inner
ClientHello is used for establishing a connection to the service, so
its contents may be influenced by other SVCB parameters. For
example, the requirements on the ProtocolNameList in Section 6.1
apply only to the inner ClientHello. Similarly, it is the inner
ClientHello whose Server Name Indication identifies the origin.
8.1. Client behavior 8.1. Client behavior
The general client behavior specified in Section 3 permits clients to The general client behavior specified in Section 3 permits clients to
retry connection with a less preferred alternative if the preferred retry connection with a less preferred alternative if the preferred
option fails, including falling back to a direct connection if all option fails, including falling back to a direct connection if all
SVCB options fail. This behavior is not suitable for ESNI, because SVCB options fail. This behavior is not suitable for ECH, because
fallback would negate the privacy benefits of ESNI. Accordingly, fallback would negate the privacy benefits of ECH. Accordingly, ECH-
ESNI-capable clients SHALL implement the following behavior for capable clients SHALL implement the following behavior for connection
connection establishment. establishment.
1. Perform connection establishment using HTTPSSVC as described in 1. Perform connection establishment using HTTPSSVC as described in
Section 3, but do not fall back to the origin's A/AAAA records. Section 3, but do not fall back to the origin's A/AAAA records.
If all the HTTPSSVC RRs have esniconfig, and they all fail, If all the HTTPSSVC RRs have an "echconfig" key, and they all
terminate connection establishment. fail, terminate connection establishment.
2. If the client implements Alt-Svc, try to connect using any 2. If the client implements Alt-Svc, try to connect using any
entries from the Alt-Svc cache. entries from the Alt-Svc cache.
3. Fall back to the origin's A/AAAA records if necessary. 3. Fall back to the origin's A/AAAA records if necessary.
As a latency optimization, clients MAY prefetch DNS records for later As a latency optimization, clients MAY prefetch DNS records for later
steps before they are needed. steps before they are needed.
8.2. Deployment considerations 8.2. Deployment considerations
An HTTPSSVC RRSet containing some RRs with esniconfig and some An HTTPSSVC RRSet containing some RRs with "echconfig" and some
without is vulnerable to a downgrade attack. This configuration is without is vulnerable to a downgrade attack. This configuration is
NOT RECOMMENDED. Zone owners who do use such a mixed configuration NOT RECOMMENDED. Zone owners who do use such a mixed configuration
SHOULD mark the RRs with esniconfig as more preferred (i.e. smaller SHOULD mark the RRs with "echconfig" as more preferred (i.e. smaller
SvcFieldPriority) than those without, in order to maximize the SvcFieldPriority) than those without, in order to maximize the
likelihood that ESNI will be used in the absence of an active likelihood that ECH will be used in the absence of an active
adversary. adversary.
9. Interaction with other standards 9. Examples
9.1. Protocol enhancements
Consider a simple zone of the form
simple.example. 300 IN A 192.0.2.1
AAAA 2001:db8::1
The domain owner could add this record
simple.example. 7200 IN HTTPSSVC 1 . alpn=h3 ...
to indicate that simple.example uses HTTPS, and supports QUIC in
addition to HTTPS over TCP (an implicit default). The record could
also include other information (e.g. non-standard port, ECH
configuration).
9.2. Apex aliasing
Consider a zone that is using CNAME aliasing:
$ORIGIN aliased.example. ; A zone that is using a hosting service
; Subdomain aliased to a high-performance server pool
www 7200 IN CNAME pool.svc.example.
; Apex domain on fixed IPs because CNAME is not allowed at the apex
@ 300 IN A 192.0.2.1
IN AAAA 2001:db8::1
With HTTPSSVC, the owner of aliased.example could alias the apex by
adding one additional record:
@ 7200 IN HTTPSSVC 0 pool.svc.example.
With this record in place, HTTPSSVC-aware clients will use the same
server pool for aliased.example and www.aliased.example. (They will
also upgrade to HTTPS on aliased.example.) Non-HTTPSSVC-aware
clients will just ignore the new record.
Similar to CNAME, HTTPSSVC has no impact on the origin name. When
connecting, clients will continue to treat the authoritative origins
as "https://www.aliased.example" and "https://aliased.example",
respectively, and will validate TLS server certificates accordingly.
9.3. Parameter binding
Suppose that svc.example's default server pool supports HTTP/2, and
it has deployed HTTP/3 on a new server pool with a different
configuration. This can be expressed in the following form:
$ORIGIN svc.example. ; A hosting provider.
pool 7200 IN HTTPSSVC 1 h3pool alpn=h2,h3 echconfig="123..."
HTTPSSVC 2 . alpn=h2 echconfig="abc..."
pool 300 IN A 192.0.2.2
AAAA 2001:db8::2
h3pool 300 IN A 192.0.2.3
AAAA 2001:db8::3
This configuration is entirely compatible with the "Apex aliasing"
example, whether the client supports HTTPSSVC or not. If the client
does support HTTPSSVC, all connections will be upgraded to HTTPS, 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, ECH
configuration, etc.
9.4. Non-HTTPS uses
For services other than HTTPS, the SVCB RR and an [Attrleaf] label
will be used. For example, to reach an example resource of
"baz://api.example.com:8765", the following Alias Form SVCB record
would be used to delegate to "svc4-baz.example.net." which in-turn
could return AAAA/A records and/or SVCB records in ServiceForm.
_8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
HTTPSSVC records use similar [Attrleaf] labels if the origin contains
a non-default port.
10. 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 OCSP Stapling [RFC6066], both of
which confer substantial performance and privacy benefits when used which confer substantial performance and privacy benefits when used
in combination with SVCB records. 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
[RFC7858] or DNS over HTTPS [RFC8484]). However, performance [RFC7858] or DNS over HTTPS [RFC8484]). However, performance
improvements, and some modest privacy improvements, are possible improvements, and some modest privacy improvements, are possible
without the use of those standards. without the use of those standards.
Any specification for use of SVCB with a protocol MUST have an entry Any specification for use of SVCB with a protocol MUST have an entry
for its scheme under the SVCB RR type in the IANA DNS Underscore for its scheme under the SVCB RR type in the IANA DNS Underscore
Global Scoped Entry Registry [Attrleaf]. The scheme SHOULD have an Global Scoped Entry Registry [Attrleaf]. The scheme SHOULD have an
entry in the IANA URI Schemes Registry [RFC7595]. The scheme SHOULD entry in the IANA URI Schemes Registry [RFC7595]. The scheme SHOULD
have a defined specification for use with SVCB. have a defined specification for use with SVCB.
10. Security Considerations 11. Security Considerations
SVCB/HTTPSSVC RRs are intended for distribution over untrusted SVCB/HTTPSSVC RRs are intended for distribution over untrusted
channels, and clients are REQUIRED to verify that the alternative channels, and clients are REQUIRED to verify that the alternative
service is authoritative for the origin (similar to Section 2.1 of service is authoritative for the origin (similar to Section 2.1 of
[AltSvc]). Therefore, DNSSEC signing and validation are OPTIONAL for [AltSvc]). Therefore, DNSSEC signing and validation are OPTIONAL for
publishing and using SVCB and HTTPSSVC records. publishing and using SVCB and HTTPSSVC records.
Clients MUST ensure that their DNS cache is partitioned for each Clients MUST ensure that their DNS cache is partitioned for each
local network, or flushed on network changes, to prevent a local local network, or flushed on network changes, to prevent a local
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.
11. IANA Considerations 12. IANA Considerations
11.1. New registry for Service Parameters 12.1. New registry for Service Parameters
The "Service Binding (SVCB) Parameter Registry" defines the name The "Service Binding (SVCB) Parameter Registry" defines the namespace
space for parameters, including string representations and numeric for parameters, including string representations and numeric
SvcParamKey values. This registry is shared with other SVCB- SvcParamKey values. This registry is shared with other SVCB-
compatible RR types, such as HTTPSSVC. compatible RR types, such as HTTPSSVC.
ACTION: create and include a reference to this registry. ACTION: create and include a reference to this registry.
11.1.1. Procedure 12.1.1. Procedure
A registration MUST include the following fields: A registration MUST include the following fields:
o Name: Service parameter key name * Name: Service parameter key name
o SvcParamKey: Service parameter key numeric identifier (range * SvcParamKey: Service parameter key numeric identifier (range
0-65535) 0-65535)
o Meaning: a short description * Meaning: a short description
* Pointer to specification text
o Pointer to specification text SvcParamKey values to be added to this namespace have different
policies ([RFC5226], Section 4.1) based on their range:
Values to be added to this name space require Expert Review (see +-------------+-------------------------+
[RFC5226], Section 4.1). Apart from the initial contents, the name | SvcParamKey | IANA Policy |
MUST NOT start with "key". +=============+=========================+
| 0-255 | Standards Action |
+-------------+-------------------------+
| 256-32767 | Expert Review |
+-------------+-------------------------+
| 32768-65280 | First Come First Served |
+-------------+-------------------------+
| 65280-65534 | Private Use |
+-------------+-------------------------+
| 65535 | Standards Action |
+-------------+-------------------------+
11.1.2. Initial contents Table 1
Apart from the initial contents, the SvcParamKey name MUST NOT start
with "key".
12.1.2. Initial contents
The "Service Binding (SVCB) Parameter Registry" shall initially be The "Service Binding (SVCB) Parameter Registry" shall initially be
populated with the registrations below: populated with the registrations below:
+-------------+-----------------+----------------------+------------+ +-------------+-----------------+---------------------+-----------+
| SvcParamKey | NAME | Meaning | Reference | | SvcParamKey | NAME | Meaning | Reference |
+-------------+-----------------+----------------------+------------+ +=============+=================+=====================+===========+
| 0 | (no name) | Reserved for | (This | | 0 | (no name) | Reserved for | (This |
| | | internal use | document) | | | | internal use | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 1 | alpn | Additional supported | (This | | 1 | alpn | Additional | (This |
| | | protocols | document) | | | | supported protocols | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 2 | no-default-alpn | No support for | (This | | 2 | no-default-alpn | No support for | (This |
| | | default protocol | document) | | | | default protocol | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 3 | port | Port for alternative | (This | | 3 | port | Port for | (This |
| | | service | document) | | | | alternative service | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 4 | ipv4hint | IPv4 address hints | (This | | 4 | ipv4hint | IPv4 address hints | (This |
| | | | document) | | | | | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 5 | esniconfig | Encrypted SNI | (This | | 5 | echconfig | Encrypted | (This |
| | | configuration | document) | | | | ClientHello info | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 6 | ipv6hint | IPv6 address hints | (This | | 6 | ipv6hint | IPv6 address hints | (This |
| | | | document) | | | | | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 65280-65534 | keyNNNNN | Private Use | (This | | 65280-65534 | keyNNNNN | Private Use | (This |
| | | | document) | | | | | document) |
| | | | | +-------------+-----------------+---------------------+-----------+
| 65535 | key65535 | Reserved | (This | | 65535 | key65535 | Reserved | (This |
| | | | document) | | | | | document) |
+-------------+-----------------+----------------------+------------+ +-------------+-----------------+---------------------+-----------+
Table 2
TODO: do we also want to reserve a range for greasing? TODO: do we also want to reserve a range for greasing?
11.2. Registry updates 12.2. Registry updates
Per [RFC6895], please add the following entry to the data type range Per [RFC6895], please add the following entries to the data type
of the Resource Record (RR) TYPEs registry: range of the Resource Record (RR) TYPEs registry:
+----------+----------------------------------------+---------------+ +----------+----------------------------------------+-----------+
| TYPE | Meaning | Reference | | TYPE | Meaning | Reference |
+----------+----------------------------------------+---------------+ +==========+========================================+===========+
| SVCB | Service Location and Parameter Binding | (This | | SVCB | Service Location and Parameter Binding | (This |
| | | document) | | | | document) |
| | | | +----------+----------------------------------------+-----------+
| HTTPSSVC | HTTPS Service Location and Parameter | (This | | HTTPSSVC | HTTPS Service Location and Parameter | (This |
| | Binding | document) | | | Binding | document) |
+----------+----------------------------------------+---------------+ +----------+----------------------------------------+-----------+
Table 3
Per [Attrleaf], please add the following entry to the DNS Underscore Per [Attrleaf], please add the following entry to the DNS Underscore
Global Scoped Entry Registry: Global Scoped Entry Registry:
+----------+------------+-----------------+-----------------+ +----------+------------+-----------------+-----------------+
| RR TYPE | _NODE NAME | Meaning | Reference | | RR TYPE | _NODE NAME | Meaning | Reference |
+----------+------------+-----------------+-----------------+ +==========+============+=================+=================+
| HTTPSSVC | _https | HTTPS SVCB info | (This document) | | HTTPSSVC | _https | HTTPS SVCB info | (This document) |
+----------+------------+-----------------+-----------------+ +----------+------------+-----------------+-----------------+
12. Acknowledgments and Related Proposals Table 4
13. Acknowledgments and Related Proposals
There have been a wide range of proposed solutions over the years to There have been a wide range of proposed solutions over the years to
the "CNAME at the Zone Apex" challenge proposed. These include the "CNAME at the Zone Apex" challenge proposed. These include
[I-D.draft-bellis-dnsop-http-record-00], [I-D.draft-bellis-dnsop-http-record-00],
[I-D.draft-ietf-dnsop-aname-03], and others. [I-D.draft-ietf-dnsop-aname-03], and others.
Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas
Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David
Benjamin, and others for their feedback and suggestions on this Benjamin, and others for their feedback and suggestions on this
draft. draft.
13. References 14. References
13.1. Normative References 14.1. 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/info/rfc7301>. July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[Attrleaf] [Attrleaf] Crocker, D., "DNS Scoped Data Through "Underscore" Naming
Crocker, D., "DNS Scoped Data Through "Underscore" Naming of Attribute Leaves", Work in Progress, Internet-Draft,
of Attribute Leaves", draft-ietf-dnsop-attrleaf-16 (work draft-ietf-dnsop-attrleaf-16, 16 November 2018,
in progress), November 2018. <http://www.ietf.org/internet-drafts/draft-ietf-dnsop-
attrleaf-16.txt>.
[base64] Josefsson, S., "The Base16, Base32, and Base64 Data [base64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>. <https://www.rfc-editor.org/info/rfc4648>.
[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/info/rfc6672>. <https://www.rfc-editor.org/info/rfc6672>.
[ESNI] Rescorla, E., Oku, K., Sullivan, N., and C. Wood, [ECH] Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
"Encrypted Server Name Indication for TLS 1.3", draft- Encrypted Client Hello", Work in Progress, Internet-Draft,
ietf-tls-esni-05 (work in progress), November 2019. draft-ietf-tls-esni-07, 1 June 2020, <http://www.ietf.org/
internet-drafts/draft-ietf-tls-esni-07.txt>.
[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/info/rfc8305>. <https://www.rfc-editor.org/info/rfc8305>.
[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/info/rfc6797>. <https://www.rfc-editor.org/info/rfc6797>.
[HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3 [HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", draft-ietf-quic-http-20 (work in progress), (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
April 2019. quic-http-20, 23 April 2019, <http://www.ietf.org/
internet-drafts/draft-ietf-quic-http-20.txt>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P.V., "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/info/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/info/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,
skipping to change at page 32, line 22 skipping to change at page 35, line 27
May 2017, <https://www.rfc-editor.org/info/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/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS [RFC8484] 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/info/rfc8484>. <https://www.rfc-editor.org/info/rfc8484>.
13.2. Informative References [WebSocket]
Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>.
14.2. 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/info/rfc7838>. April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[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/info/rfc8499>. January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[FETCH] "Fetch Living Standard", May 2020,
<https://fetch.spec.whatwg.org/>.
[I-D.draft-bellis-dnsop-http-record-00] [I-D.draft-bellis-dnsop-http-record-00]
Bellis, R., "A DNS Resource Record for HTTP", draft- Bellis, R., "A DNS Resource Record for HTTP", Work in
bellis-dnsop-http-record-00 (work in progress), November Progress, Internet-Draft, draft-bellis-dnsop-http-record-
2018. 00, 3 November 2018, <http://www.ietf.org/internet-drafts/
draft-bellis-dnsop-http-record-00.txt>.
[I-D.draft-ietf-dnsop-aname-03] [I-D.draft-ietf-dnsop-aname-03]
Finch, T., Hunt, E., Dijk, P., Eden, A., and W. Mekking, Finch, T., Hunt, E., Dijk, P., Eden, A., and W. Mekking,
"Address-specific DNS aliases (ANAME)", draft-ietf-dnsop- "Address-specific DNS aliases (ANAME)", Work in Progress,
aname-03 (work in progress), April 2019. Internet-Draft, draft-ietf-dnsop-aname-03, 15 April 2019,
<http://www.ietf.org/internet-drafts/draft-ietf-dnsop-
aname-03.txt>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] 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/info/rfc2782>. <https://www.rfc-editor.org/info/rfc2782>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA [RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <https://www.rfc-editor.org/info/rfc6895>. April 2013, <https://www.rfc-editor.org/info/rfc6895>.
13.3. URIs [URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
[1] https://github.com/MikeBishop/dns-alt-svc RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
Appendix A. Comparison with alternatives Appendix A. Comparison with alternatives
The SVCB and HTTPSSVC record types closely resemble, and are inspired The SVCB and HTTPSSVC record types closely resemble, and are inspired
by, some existing record types and proposals. A complaint with all by, some existing record types and proposals. A complaint with all
of the alternatives is that web clients have seemed unenthusiastic of the alternatives is that web clients have seemed unenthusiastic
about implementing them. The hope here is that by providing an about implementing them. The hope here is that by providing an
extensible solution that solves multiple problems we will overcome extensible solution that solves multiple problems we will overcome
the inertia and have a path to achieve client implementation. the inertia and have a path to achieve client implementation.
A.1. Differences from the SRV RR type A.1. Differences from the SRV RR type
An SRV record [RFC2782] can perform a similar function to the SVCB An SRV record [RFC2782] can perform a similar function to the SVCB
record, informing a client to look in a different location for a record, informing a client to look in a different location for a
service. However, there are several differences: service. However, there are several differences:
o SRV records are typically mandatory, whereas clients will always * SRV records are typically mandatory, whereas clients will always
continue to function correctly without making use of SVCB. continue to function correctly without making use of SVCB.
o 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).
o SRV records are not extensible, whereas SVCB and HTTPSSVC can be * SRV records are not extensible, whereas SVCB and HTTPSSVC can be
extended with new parameters. extended with new parameters.
A.2. Differences from the proposed HTTP record A.2. Differences from the proposed HTTP record
Unlike [I-D.draft-bellis-dnsop-http-record-00], this approach is Unlike [I-D.draft-bellis-dnsop-http-record-00], this approach is
extensible to cover Alt-Svc and ESNI use-cases. Like that proposal, extensible to cover Alt-Svc and Encrypted ClientHello use-cases.
this addresses the zone apex CNAME challenge. Like that proposal, this 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.
A.3. Differences from the proposed ANAME record A.3. Differences from the proposed ANAME record
Unlike [I-D.draft-ietf-dnsop-aname-03], this approach is extensible Unlike [I-D.draft-ietf-dnsop-aname-03], this approach is extensible
to cover Alt-Svc and ESNI use-cases. This approach also does not to cover Alt-Svc and ECH use-cases. This approach also does not
require any changes or special handling on either authoritative or require any changes or special handling on either authoritative or
master servers, beyond optionally returning in-bailiwick additional master servers, beyond optionally returning in-bailiwick additional
records. 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.
A.4. Differences from the proposed ESNI record A.4. Comparison with separate RR types for AliasForm and ServiceForm
Unlike [ESNI], this approach is extensible and covers the Alt-Svc
case as well as addresses the zone apex CNAME challenge.
By mirroring the Alt-Svc model we also provide a way to solve the
ESNI multi-CDN challenges in a general case.
Unlike ESNI, SVCB allows specifying different ESNI configurations for Abstractly, functions of AliasForm and ServiceForm are independent,
different protocols and ports, rather than applying a single so it might be tempting to specify them as separate RR types.
configuration to all ports on a domain. However, this would result in a serious performance impairment,
because clients cannot rely on their recursive resolver to follow
SVCB aliases (unlike CNAME). Thus, clients would have to issue
queries for both RR types in parallel, potentially at each step of
the alias chain. Recursive resolvers that implement the
specification would, upon receipt of a ServiceForm query, emit both a
ServiceForm and an AliasForm query to the authoritative. Thus,
splitting the RR type would double, or in some cases triple, the load
on clients and servers, and would not reduce implementation
complexity.
Appendix B. Design Considerations and Open Issues Appendix B. Design Considerations and Open Issues
This draft is intended to be a work-in-progress for discussion. Many This draft is intended to be a work-in-progress for discussion. Many
details are expected to change with subsequent refinement. Some details are expected to change with subsequent refinement. Some
known issues or topics for discussion are listed below. known issues or topics for discussion are listed below.
B.1. Record Name B.1. Record Name
Naming is hard. "SVCB" and "HTTPSSVC" are proposed as placeholders Naming is hard. "SVCB" and "HTTPSSVC" are proposed as placeholders
that are easy to search for and replace when a final name is chosen. that are easy to search for and replace when a final name is chosen.
Other names for this record might include B, ALTSVC, HTTPS, HTTPSSRV, Other names for this record might include B, ALTSVC, HTTPS, HTTPSSRV,
HTTPSSVC, SVCHTTPS, or something else. HTTPSSVC, SVCHTTPS, or something else.
B.2. Generality B.2. Generality
The SVCB record was designed as a generalization of HTTPSSVC, based The SVCB record was designed as a generalization of HTTPSSVC, based
on feedback requesting a solution that applied to protocols pther on feedback requesting a solution that applied to protocols other
than HTTP. Past efforts to over-generalize have not met with broad than HTTP. Past efforts to over-generalize have not met with broad
success, but we hope that HTTPSSVC and SVCB have struck an acceptable success, but we hope that HTTPSSVC and SVCB have struck an acceptable
balance between generality and focus. balance between generality and focus.
B.3. Wire Format B.3. Wire Format
Advice from experts in DNS wire format best practices would be Advice from experts in DNS wire format best practices would be
greatly appreciated to refine the proposed details, overall. greatly appreciated to refine the proposed details, overall.
B.4. Whether to include Weight B.4. Whether to include Weight
Some other similar mechanisms such as SRV have a weight in-addition Some other similar mechanisms such as SRV have a weight in addition
to priority. That is excluded here for simplicity. It could always to priority. That is excluded here for simplicity. It could always
be added as an optional SVCB parameter. be added as an optional SVCB parameter.
Appendix C. Change history Appendix C. Change history
o draft-ietf-dnsop-svcb-httpssvc-01 * draft-ietf-dnsop-svcb-httpssvc-03
* Reduce the emphasis on conversion between HTTPSSVC and Alt-Svc - Revised chain length limit requirements
* Make the "untrusted channel" concept more precise. - Revised IANA registry rules for SvcParamKeys
* Make SvcFieldPriority = 0 the definition of AliasForm, instead - 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. of a requirement.
o draft-ietf-dnsop-svcb-httpssvc-00 * draft-ietf-dnsop-svcb-httpssvc-00
* Document an optimization for optimistic pre-connection. (Chris - Document an optimization for optimistic pre-connection. (Chris
Wood) Wood)
* Relax IP hint handling requirements. (Eric Rescorla) - Relax IP hint handling requirements. (Eric Rescorla)
o draft-nygren-dnsop-svcb-httpssvc-00 * draft-nygren-dnsop-svcb-httpssvc-00
* Generalize to an SVCB record, with special-case handling for - Generalize to an SVCB record, with special-case handling for
Alt-Svc and HTTPS separated out to dedicated sections. Alt-Svc and HTTPS separated out to dedicated sections.
* Split out a separate HTTPSSVC record for the HTTPS use-case. - Split out a separate HTTPSSVC record for the HTTPS use-case.
* Remove the explicit SvcRecordType=0/1 and instead make the - Remove the explicit SvcRecordType=0/1 and instead make the
AliasForm vs ServiceForm be implicit. This was based on AliasForm vs ServiceForm be implicit. This was based on
feedback recommending against subtyping RR type. feedback recommending against subtyping RR type.
* Remove one optimization. - Remove one optimization.
o draft-nygren-httpbis-httpssvc-03 * draft-nygren-httpbis-httpssvc-03
* Change redirect type for HSTS-style behavior from 302 to 307 to - Change redirect type for HSTS-style behavior from 302 to 307 to
reduce ambiguities. reduce ambiguities.
o draft-nygren-httpbis-httpssvc-02 * draft-nygren-httpbis-httpssvc-02
* Remove the redundant length fields from the wire format. - Remove the redundant length fields from the wire format.
* Define a SvcDomainName of "." for SvcRecordType=1 as being the - Define a SvcDomainName of "." for SvcRecordType=1 as being the
HTTPSSVC RRNAME. HTTPSSVC RRNAME.
* Replace "hq" with "h3". - Replace "hq" with "h3".
o draft-nygren-httpbis-httpssvc-01 * draft-nygren-httpbis-httpssvc-01
* Fixes of record name. Replace references to "HTTPSVC" with - Fixes of record name. Replace references to "HTTPSVC" with
"HTTPSSVC". "HTTPSSVC".
o draft-nygren-httpbis-httpssvc-00 * draft-nygren-httpbis-httpssvc-00
* Initial version - Initial version
Authors' Addresses Authors' Addresses
Ben Schwartz Ben Schwartz
Google Google
Email: bemasc@google.com Email: bemasc@google.com
Mike Bishop Mike Bishop
Akamai Technologies Akamai Technologies
 End of changes. 171 change blocks. 
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