DNSOP Working Group B. Schwartz
Internet-Draft Google
Intended status: Standards Track M. Bishop
Expires: January 14, 2021 E. Nygren
Akamai Technologies
July 13, 2020
Service binding and parameter specification via the DNS (DNS SVCB and
HTTPS RRs)
draft-ietf-dnsop-svcb-https-01
Abstract
This document specifies the "SVCB" and "HTTPS" DNS resource record
(RR) types to facilitate the lookup of information needed to make
connections to network services, such as for HTTPS origins. SVCB
records allow a service to be provided from multiple alternative
endpoints, each with associated parameters (such as transport
protocol configuration and keys for encrypting the TLS ClientHello).
They also enable aliasing of apex domains, which is not possible with
CNAME. The HTTPS RR is a variation of SVCB for HTTPS and HTTP
origins. By providing more information to the client before it
attempts to establish a connection, these records offer potential
benefits to both performance and privacy.
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
standing desires to have SRV or a functional equivalent implemented
for HTTP). These proposals each provide an important function but
are potentially incompatible with each other, such as when an origin
is load-balanced across multiple hosting providers (multi-CDN).
Furthermore, these each add potential cases for adding additional
record lookups in addition to AAAA/A lookups. This design attempts
to provide a unified framework that encompasses the key functionality
of these proposals, as well as providing some extensibility for
addressing similar future challenges.
TO BE REMOVED: This document is being collaborated on in Github at:
https://github.com/MikeBishop/dns-alt-svc [1]. The most recent
working version of the document, open issues, etc. should all be
available there. The authors (gratefully) accept pull requests.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Goals of the SVCB RR . . . . . . . . . . . . . . . . . . 5
1.2. Overview of the SVCB RR . . . . . . . . . . . . . . . . . 6
1.3. Parameter for Encrypted ClientHello . . . . . . . . . . . 7
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2. The SVCB record type . . . . . . . . . . . . . . . . . . . . 7
2.1. Zone file presentation format . . . . . . . . . . . . . . 8
2.2. RDATA wire format . . . . . . . . . . . . . . . . . . . . 9
2.3. SVCB owner names . . . . . . . . . . . . . . . . . . . . 10
2.4. Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.1. AliasMode . . . . . . . . . . . . . . . . . . . . . . 11
2.4.2. ServiceMode . . . . . . . . . . . . . . . . . . . . . 12
2.4.3. SvcPriority . . . . . . . . . . . . . . . . . . . . . 12
2.5. Special handling of "." in TargetName . . . . . . . . . . 12
2.5.1. AliasMode . . . . . . . . . . . . . . . . . . . . . . 13
2.5.2. ServiceMode . . . . . . . . . . . . . . . . . . . . . 13
3. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 13
3.1. Handling resolution failures . . . . . . . . . . . . . . 14
3.2. Clients using a Proxy . . . . . . . . . . . . . . . . . . 14
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4. DNS Server Behavior . . . . . . . . . . . . . . . . . . . . . 15
4.1. Authoritative servers . . . . . . . . . . . . . . . . . . 15
4.2. Recursive resolvers . . . . . . . . . . . . . . . . . . . 15
4.3. General requirements . . . . . . . . . . . . . . . . . . 16
5. Performance optimizations . . . . . . . . . . . . . . . . . . 16
5.1. Optimistic pre-connection and connection reuse . . . . . 17
5.2. Generating and using incomplete responses . . . . . . . . 17
5.3. Structuring zones for performance . . . . . . . . . . . . 18
6. Initial SvcParamKeys . . . . . . . . . . . . . . . . . . . . 18
6.1. "alpn" and "no-default-alpn" . . . . . . . . . . . . . . 18
6.2. "port" . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.3. "echconfig" . . . . . . . . . . . . . . . . . . . . . . . 20
6.4. "ipv4hint" and "ipv6hint" . . . . . . . . . . . . . . . . 21
6.5. "mandatory" . . . . . . . . . . . . . . . . . . . . . . . 22
7. Using SVCB with HTTPS and HTTP . . . . . . . . . . . . . . . 22
7.1. Owner names for HTTPS RRs . . . . . . . . . . . . . . . . 23
7.2. Relationship to Alt-Svc . . . . . . . . . . . . . . . . . 24
7.2.1. ALPN usage . . . . . . . . . . . . . . . . . . . . . 24
7.2.2. Untrusted channel . . . . . . . . . . . . . . . . . . 24
7.2.3. TTL and granularity . . . . . . . . . . . . . . . . . 24
7.3. Interaction with Alt-Svc . . . . . . . . . . . . . . . . 25
7.4. Requiring Server Name Indication . . . . . . . . . . . . 25
7.5. HTTP Strict Transport Security . . . . . . . . . . . . . 25
7.6. HTTP-based protocols . . . . . . . . . . . . . . . . . . 26
8. SVCB/HTTPS RR parameter for ECH configuration . . . . . . . . 26
8.1. Client behavior . . . . . . . . . . . . . . . . . . . . . 27
8.2. Deployment considerations . . . . . . . . . . . . . . . . 27
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Protocol enhancements . . . . . . . . . . . . . . . . . . 27
9.2. Apex aliasing . . . . . . . . . . . . . . . . . . . . . . 28
9.3. Parameter binding . . . . . . . . . . . . . . . . . . . . 28
9.4. Non-HTTPS uses . . . . . . . . . . . . . . . . . . . . . 29
10. Interaction with other standards . . . . . . . . . . . . . . 29
11. Security Considerations . . . . . . . . . . . . . . . . . . . 29
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
12.1. SVCB RRType . . . . . . . . . . . . . . . . . . . . . . 30
12.2. HTTPS RRType . . . . . . . . . . . . . . . . . . . . . . 30
12.3. New registry for Service Parameters . . . . . . . . . . 31
12.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . 31
12.3.2. Initial contents . . . . . . . . . . . . . . . . . . 31
12.4. Registry updates . . . . . . . . . . . . . . . . . . . . 32
13. Acknowledgments and Related Proposals . . . . . . . . . . . . 33
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
14.1. Normative References . . . . . . . . . . . . . . . . . . 33
14.2. Informative References . . . . . . . . . . . . . . . . . 36
14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Appendix A. Decoding text in zone files . . . . . . . . . . . . 37
A.1. Decoding a value list . . . . . . . . . . . . . . . . . . 37
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Appendix B. Comparison with alternatives . . . . . . . . . . . . 38
B.1. Differences from the SRV RR type . . . . . . . . . . . . 38
B.2. Differences from the proposed HTTP record . . . . . . . . 39
B.3. Differences from the proposed ANAME record . . . . . . . 39
B.4. Comparison with separate RR types for AliasMode and
ServiceMode . . . . . . . . . . . . . . . . . . . . . . . 39
Appendix C. Change history . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction
The SVCB and HTTPS RRs provide clients with complete instructions for
access to a service. This information enables improved performance
and privacy by avoiding transient connections to a sub-optimal
default server, negotiating a preferred protocol, and providing
relevant public keys.
For example, when clients need to make a connection to fetch
resources associated with an HTTPS URI, they currently resolve only A
and/or AAAA records for the origin hostname. This is adequate for
services that use basic HTTPS (fixed port, no QUIC, no [ECH]). Going
beyond basic HTTPS confers privacy, performance, and operational
advantages, but it requires the client to learn additional
information, and it is highly desirable to minimize the number of
round-trips and lookups required to learn this additional
information.
The SVCB and HTTPS RRs also help when the operator of a service
wishes to delegate operational control to one or more other domains,
e.g. delegating the origin "https://example.com" to a service
operator endpoint at "svc.example.net". While this case can
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
bound collection of consistent configuration parameters through the
DNS (such as network location, protocol, and keying information).
This document first describes the SVCB RR as a general-purpose
resource record that can be applied directly and efficiently to a
wide range of services (Section 2). The HTTPS RR is then defined as
a special case of SVCB that improves efficiency and convenience for
use with HTTPS (Section 7) by avoiding the need for an Attrleaf label
[Attrleaf] (Section 7.1). Other protocols with similar needs may
follow the pattern of HTTPS and assign their own SVCB-compatible RR
types.
All behaviors described as applying to the SVCB RR also apply to the
HTTPS RR unless explicitly stated otherwise. Section 7 describes
additional behaviors specific to the HTTPS RR. Apart from Section 7
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and introductory examples, much of this document refers only to the
SVCB RR, but those references should be taken to apply to SVCB,
HTTPS, and any future SVCB-compatible RR types.
The SVCB RR has two modes: 1) "AliasMode" simply delegates
operational control for a resource; 2) "ServiceMode" binds together
configuration information for a service endpoint. ServiceMode
provides additional key=value parameters within each RDATA set.
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
is an instantiation of SVCB for authoritative nameserver delegation
and parameter specification, similar to HTTPS. See [I-D.tapril-ns2]
as one example.
1.1. Goals of the SVCB RR
The goal of the SVCB RR is to allow clients to resolve a single
additional DNS RR in a way that:
o Provides alternative endpoints that are authoritative for the
service, along with parameters associated with each of these
endpoints.
o Does not assume that all alternative endpoints have the same
parameters or capabilities, or are even operated by the same
entity. This is important as DNS does not provide any way to tie
together multiple RRs for the same name. For example, if
www.example.com is a CNAME alias that switches between one of
three CDNs or hosting environments, successive queries for that
name may return records that correspond to different environments.
o Enables CNAME-like functionality at a zone apex (such as
"example.com") for participating protocols, and generally enables
delegation of operational authority for an origin within the DNS
to an alternate name.
Additional goals specific to HTTPS RRs and the HTTPS use-case
include:
o Connect directly to HTTP3 (QUIC transport) alternative endpoints
[HTTP3]
o Obtain the Encrypted ClientHello [ECH] keys associated with an
alternative endpoint
o Support non-default TCP and UDP ports
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o Enable SRV-like benefits (e.g. apex delegation, as mentioned
above) for HTTP(S), where SRV [SRV] has not been widely adopted
o Provide an HSTS-like indication [HSTS] signaling that the HTTPS
scheme should be used instead of HTTP for this request (see
Section 7.5).
1.2. Overview of the SVCB RR
This subsection briefly describes the SVCB RR in a non-normative
manner. (As mentioned above, this all applies equally to the HTTPS
RR which shares the same encoding, format, and high-level semantics.)
The SVCB RR has two modes: AliasMode, which aliases a name to another
name, and ServiceMode, which provides connection information bound to
a service endpoint domain. Placing both forms in a single RR type
allows clients to fetch the relevant information with a single query.
The SVCB RR has two mandatory fields and one optional. The fields
are:
1. SvcPriority: The priority of this record (relative to others,
with lower values preferred). A value of 0 indicates AliasMode.
(Described in Section 2.4.3.)
2. TargetName: The domain name of either the alias target (for
AliasMode) or the alternative endpoint (for ServiceMode).
3. SvcParams (optional): A list of key=value pairs describing the
alternative endpoint at TargetName (only used in ServiceMode and
otherwise ignored). Described in Section 2.1.
Cooperating DNS recursive resolvers will perform subsequent record
resolution (for SVCB, A, and AAAA records) and return them in the
Additional Section of the response. Clients either use responses
included in the additional section returned by the recursive resolver
or perform necessary SVCB, A, and AAAA record resolutions. DNS
authoritative servers can attach in-bailiwick SVCB, A, AAAA, and
CNAME records in the Additional Section to responses for a SVCB
query.
In ServiceMode, the SvcParams of the SVCB RR provide an extensible
data model for describing alternative endpoints that are
authoritative for the origin, along with parameters associated with
each of these alternative endpoints.
For the HTTPS use-case, the HTTPS RR enables many of the benefits of
Alt-Svc [AltSvc] without waiting for a full HTTP connection
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initiation (multiple roundtrips) before learning of the preferred
alternative, and without necessarily revealing the user's intended
destination to all entities along the network path.
1.3. Parameter for Encrypted ClientHello
This document also defines a parameter for Encrypted ClientHello
[ECH] keys. See Section 8.
1.4. Terminology
Our terminology is based on the common case where the SVCB record is
used to access a resource identified by a URI whose "authority" field
contains a DNS hostname as the "host".
o The "service" is the information source identified by the
"authority" and "scheme" of the URI, capable of providing access
to the resource. For HTTPS URIs, the "service" corresponds to an
HTTPS "origin" [RFC6454].
o The "service name" is the "host" portion of the authority.
o The "authority endpoint" is the authority's hostname and a port
number implied by the scheme or specified in the URI.
o An "alternative endpoint" is a hostname, port number, and other
associated instructions to the client on how to reach an instance
of service.
Additional DNS terminology intends to be consistent with [DNSTerm].
SVCB is a contraction of "service binding". The SVCB RR, HTTPS RR,
and future RR types that share SVCB's format and registry are
collectively known as SVCB-compatible RR types.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. The SVCB record type
The SVCB DNS resource record (RR) type (RR type 64) is used to locate
alternative endpoints for a service.
The algorithm for resolving SVCB records and associated address
records is specified in Section 3.
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Other SVCB-compatible resource record types can also be defined as-
needed. In particular, the HTTPS RR (RR type 65) provides special
handling for the case of "https" origins as described in Section 7.
SVCB RRs are extensible by a list of SvcParams, which are pairs
consisting of a SvcParamKey and a SvcParamValue. Each SvcParamKey
has a presentation name and a registered number. Values are in a
format specific to the SvcParamKey. Their definition should specify
both their presentation format and wire encoding (e.g., domain names,
binary data, or numeric values). The initial SvcParamKeys and
formats are defined in Section 6.
2.1. Zone file presentation format
The presentation format of the record is:
Name TTL IN SVCB SvcPriority TargetName SvcParams
The SVCB record is defined specifically within the Internet ("IN")
Class ([RFC1035]).
SvcPriority is a number in the range 0-65535, TargetName is a domain
name, and the SvcParams are a whitespace-separated list, with each
SvcParam consisting of a SvcParamKey=SvcParamValue pair or a
standalone SvcParamKey. SvcParamKeys are subject to IANA control
(Section 12.3).
Each SvcParamKey SHALL appear at most once in the SvcParams. In
presentation format, SvcParamKeys are lower-case alphanumeric
strings. Key names should contain 1-63 characters from the ranges
"a"-"z", "0"-"9", and "-". In ABNF [RFC5234],
alpha-lc = %x61-7A ; a-z
SvcParamKey = 1*63(alpha-lc / DIGIT / "-")
SvcParam = SvcParamKey ["=" SvcParamValue]
SvcParamValue = char-string
value = *OCTET
The definition of each SvcParamKey indicates that its SvcParamValue
is empty, single-valued, or multi-valued. To parse a single-valued
SvcParam, the parser applies the character-string decoding algorithm
(Appendix A), producing a "value", and then performs key-specific
processing to validate the input and produce the wire-format
encoding. To parse a multi-valued SvcParam, the parser applies the
value-list decoding algorithm to the "char-string" (Appendix A.1),
splitting on unescaped commas to produce a list of zero or more
values.
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When the "=" is omitted, the "value" or value list is interpreted as
empty.
Unrecognized keys are represented in presentation format as
"keyNNNNN" where NNNNN is the numeric value of the key type without
leading zeros. SvcParams in this form are always treated as single-
valued, and the decoded "value" SHALL be used as its wire format
encoding.
SvcParams in presentation format MAY appear in any order, but keys
MUST NOT be repeated.
2.2. RDATA wire format
The RDATA for the SVCB RR consists of:
o a 2 octet field for SvcPriority as an integer in network byte
order.
o the uncompressed, fully-qualified TargetName, represented as a
sequence of length-prefixed labels as in Section 3.1 of [RFC1035].
o the SvcParams, consuming the remainder of the record (so smaller
than 65535 octets and constrained by the RDATA and DNS message
sizes).
When the list of SvcParams is non-empty (ServiceMode), it contains a
series of SvcParamKey=SvcParamValue pairs, represented as:
o a 2 octet field containing the SvcParamKey as an integer in
network byte order. (See Section 12.3.2 for the defined values.)
o a 2 octet field containing the length of the SvcParamValue as an
integer between 0 and 65535 in network byte order (but constrained
by the RDATA and DNS message sizes).
o an octet string of this length whose contents are in a format
determined by the SvcParamKey.
SvcParamKeys SHALL appear in increasing numeric order.
Clients MUST consider an RR malformed if:
o the parser reaches the end of the RDATA while parsing the
SvcParams.
o SvcParamKeys are not in strictly increasing numeric order.
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o the SvcParamValue for an SvcParamKey does not have the expected
format.
Note that the second condition implies that there are no duplicate
SvcParamKeys.
If any RRs are malformed, the client MUST reject the entire RRSet and
fall back to non-SVCB connection establishment.
2.3. SVCB owner names
When querying the SVCB RR, a service is translated into a QNAME by
prepending the service name with a label indicating the scheme,
prefixed with an underscore, resulting in a domain name like
"_examplescheme.api.example.com.".
Protocol mapping documents MAY specify additional underscore-prefixed
labels to be prepended. For schemes that specify a port
(Section 3.2.3 of [URI]), one reasonable possibility is to prepend
the indicated port number (or the default if no port number is
specified). We term this behavior "Port Prefix Naming", and use it
in the examples throughout this document.
See Section 7.1 for the HTTPS RR behavior.
When a prior CNAME or SVCB record has aliased to a SVCB record, each
RR shall be returned under its own owner name.
Note that none of these forms alter the origin or authority for
validation purposes. For example, TLS clients MUST continue to
validate TLS certificates for the original service name.
As an example, the owner of example.com could publish this record:
_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. (
alpn="bar" port="8004" echconfig="..." )
to indicate that these services are served on port number 8004, which
supports the protocol "bar" and its associated transport in addition
to the default transport protocol for "foo://".
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(Parentheses are used to ignore a line break ([RFC1035]
Section 5.1).)
2.4. Modes
When SvcPriority is 0 the SVCB record is in AliasMode. Otherwise, it
is in ServiceMode.
Within a SVCB RRSet, all RRs SHOULD have the same Mode. If an RRSet
contains a record in AliasMode, the recipient MUST ignore any
ServiceMode records in the set.
2.4.1. AliasMode
In AliasMode, the SVCB record aliases a service to a TargetName.
SVCB RRSets SHOULD only have a single resource record in AliasMode.
If multiple are present, clients or recursive resolvers SHOULD pick
one at random.
The primary purpose of AliasMode is to allow aliasing at the zone
apex, where CNAME is not allowed. In AliasMode, TargetName MUST be
the name of a domain that has SVCB, AAAA, or A records. It MUST NOT
be equal to the owner name, as this would cause a loop.
For example, the operator of foo://example.com:8080 could point
requests to a service operating at foosvc.example.net by publishing:
_8080._foo.example.com. 3600 IN SVCB 0 foosvc.example.net.
Using AliasMode maintains a separation of concerns: the owner of
foosvc.example.net can add or remove ServiceMode SVCB records without
requiring a corresponding change to example.com. Note that if
foosvc.example.net promises to always publish a SVCB record, this
AliasMode record can be replaced by a CNAME, which would likely
improve performance.
AliasMode is especially useful for SVCB-compatible RR types that do
not require an underscore prefix, such as the HTTPS RR type. For
example, the operator of https://example.com could point requests to
a server at svc.example.net by publishing this record at the zone
apex:
example.com. 3600 IN HTTPS 0 svc.example.net.
Note that the SVCB record's owner name MAY be the canonical name of a
CNAME record, and the TargetName MAY be the owner of a CNAME record.
Clients and recursive resolvers MUST follow CNAMEs as normal.
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To avoid unbounded alias chains, clients and recursive resolvers MUST
impose a limit on the total number of SVCB aliases they will follow
for each resolution request. This limit MUST NOT be zero, i.e.
implementations MUST be able to follow at least one AliasMode 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 AliasMode records.
As legacy clients will not know to use this record, service operators
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
might offer better performance, and therefore would be preferable for
clients implementing this specification to use.
AliasMode records only apply to queries for the specific RR type.
For example, a SVCB record cannot alias to an HTTPS record, nor vice-
versa.
2.4.2. ServiceMode
In ServiceMode, the TargetName and SvcParams within each resource
record associate an alternative endpoint for the service with its
connection parameters.
Each protocol scheme that uses SVCB MUST define a protocol mapping
that explains how SvcParams are applied for connections of that
scheme. Unless specified otherwise by the protocol mapping, clients
MUST ignore any SvcParam that they do not recognize.
2.4.3. SvcPriority
RRSets are explicitly unordered collections, so the SvcPriority field
is used to impose an ordering on SVCB RRs. SVCB RRs with a smaller
SvcPriority value SHOULD be given preference over RRs with a larger
SvcPriority value.
When receiving an RRSet containing multiple SVCB records with the
same SvcPriority value, clients SHOULD apply a random shuffle within
a priority level to the records before using them, to ensure uniform
load-balancing.
2.5. Special handling of "." in TargetName
If TargetName has the value "." (represented in the wire format as a
zero-length label), special rules apply.
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2.5.1. AliasMode
For AliasMode SVCB RRs, a TargetName of "." indicates that the
service is not available or does not exist. This indication is
advisory: clients encountering this indication MAY ignore it and
attempt to connect without the use of SVCB.
2.5.2. ServiceMode
For ServiceMode SVCB RRs, if TargetName has the value ".", then the
owner name of this record MUST be used as the effective TargetName.
For example, in the following example "svc2.example.net" is the
effective TargetName:
example.com. 7200 IN HTTPS 0 svc.example.net.
svc.example.net. 7200 IN CNAME svc2.example.net.
svc2.example.net. 7200 IN HTTPS 1 . port=8002 echconfig="..."
svc2.example.net. 300 IN A 192.0.2.2
svc2.example.net. 300 IN AAAA 2001:db8::2
3. Client behavior
A SVCB-aware client selects an endpoint for a service using the
following procedure:
1. Let $ADDR_QNAME be the service name. Let $SVCB_QNAME be the
service name plus appropriate prefixes for the scheme (see
Section 2.3).
2. In parallel, issue AAAA/A queries for $ADDR_QNAME and a SVCB
query for $SVCB_QNAME. The answers for these may or may not
include CNAME pointers before reaching one or more of these
records.
3. If an AliasMode SVCB record is returned for $SVCB_QNAME, clients
MUST set $ADDR_QNAME and $SVCB_QNAME to its TargetName (without
additional prefixes) and loop back to step 2, subject to chain
length limits and loop detection heuristics (see Section 3.1).
4. If one or more ServiceMode records are returned for $SVCB_QNAME,
clients SHOULD select the highest-priority compatible record with
acceptable parameters. This TargetName and SvcParams represent
the preferred endpoint. If connection to this endpoint fails,
the client MAY try to connect using values from a lower-priority
record. If all attempts fail, clients SHOULD go to step 5.
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5. Try to use the endpoint consisting of $ADDR_QNAME, the authority
endpoint's port number, and no SvcParams.
6. If all of the above connection attempts fail, clients MAY connect
to the authority endpoint.
This procedure does not rely on any recursive or authoritative DNS
server to comply with this specification or have any awareness of
SVCB.
When selecting between AAAA and A records to use, clients may use an
approach such as Happy Eyeballs [HappyEyeballsV2].
Some important optimizations are discussed in Section 5 to avoid
additional latency in comparison to ordinary AAAA/A lookups.
3.1. Handling resolution failures
If a SVCB query results in a SERVFAIL error, transport error, or
timeout, and DNS exchanges between the client and the recursive
resolver are cryptographically protected (e.g. using TLS [DoT] or
HTTPS [DoH]), the client SHOULD NOT fall back to $ADDR_QNAME or the
authority endpoint (steps 5 and 6 above). Otherwise, an active
attacker could mount a downgrade attack by denying the user access to
the SvcParams.
A SERVFAIL error can occur if the domain is DNSSEC-signed, the
recursive resolver is DNSSEC-validating, and the attacker is between
the recursive resolver and the authoritative DNS server. A transport
error or timeout can occur if an active attacker between the client
and the recursive resolver is selectively dropping SVCB queries or
responses, based on their size or other observable patterns.
Similarly, if the client enforces DNSSEC validation on A/AAAA
responses, it SHOULD NOT fall back to steps 5 or 6 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 the authority endpoint,
as if the origin's SVCB record did not exist.
3.2. Clients using a Proxy
Clients using a domain-oriented transport proxy like HTTP CONNECT
([RFC7231] Section 4.3.6) or SOCKS5 ([RFC1928]) have the option to
use named destinations, in which case the client does not perform any
A or AAAA queries for destination domains. If the client is using
named destinations with a proxy that does not provide SVCB query
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capability (e.g. through an affiliated DNS resolver), the client
would have to perform SVCB queries though a separate resolver. This
might disclose the client's destinations to an additional party,
creating privacy concerns. If these concerns apply, the client
SHOULD disable SVCB resolution.
If the client does use SVCB and named destinations, the client SHOULD
follow the standard SVCB resolution process, selecting the smallest-
SvcPriority option that is compatible with the client and the proxy.
The client SHOULD provide the final TargetName and port to the proxy,
which will perform any required A and AAAA lookups.
Providing the proxy with the final TargetName has several benefits:
o It allows the client to use the SvcParams, if present, which is
only usable with a specific TargetName. The SvcParams may include
information that enhances performance (e.g. alpn) and privacy
(e.g. echconfig).
o It allows the service to delegate the apex domain.
o It allows the proxy to select between IPv4 and IPv6 addresses for
the server according to its configuration, and receive addresses
based on its network geolocation.
4. DNS Server Behavior
4.1. Authoritative servers
When replying to a SVCB query, authoritative DNS servers SHOULD
return A, AAAA, and SVCB records in the Additional Section for any
in-bailiwick TargetNames. If the zone is signed, the server SHOULD
also include positive or negative DNSSEC responses for these records
in the Additional section.
4.2. Recursive resolvers
Recursive resolvers that are aware of SVCB SHOULD help the client to
execute the procedure in Section 3 with minimum overall latency, by
incorporating additional useful information into the response. For
the initial SVCB record query, this is just the normal response
construction process (i.e. unknown RR type resolution under
[RFC3597]). For followup resolutions performed during this
procedure, we define incorporation as adding all useful RRs from the
response to the Additional section without altering the response
code.
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Upon receiving a SVCB query, recursive resolvers SHOULD start with
the standard resolution procedure, and then follow this procedure to
construct the full response to the stub resolver:
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 AliasMode, choose one
of them at random, and resolve SVCB, A, and AAAA records for its
TargetName.
* If any SVCB records are resolved, go to step 1.
* Otherwise, incorporate the results of A and AAAA resolution,
and terminate.
3. All the resolved SVCB records are in ServiceMode. Resolve A and
AAAA queries for each TargetName (or for the owner name if
TargetName is "."), incorporate all the results, and terminate.
In this procedure, "resolve" means the resolver's ordinary recursive
resolution procedure, as if processing a query for that RRSet. This
includes following any aliases that the resolver would ordinarily
follow (e.g. CNAME, DNAME [DNAME]).
See Section 5.2 for possible optimizations of this procedure.
4.3. General requirements
Recursive resolvers SHOULD treat the SvcParams portion of the SVCB RR
as opaque and SHOULD NOT try to alter their behavior based on its
contents.
When responding to a query that includes the DNSSEC OK bit
([RFC3225]), DNSSEC-capable recursive and authoritative DNS servers
MUST accompany each RRSet in the Additional section with the same
DNSSEC-related records that they would send when providing that RRSet
as an Answer (e.g. RRSIG, NSEC, NSEC3).
5. Performance optimizations
For optimal performance (i.e. minimum connection setup time), clients
SHOULD issue address (AAAA and/or A) and SVCB queries simultaneously,
and SHOULD implement a client-side DNS cache. Responses in the
Additional section of a SVCB response SHOULD be placed in cache
before performing any followup queries. With these optimizations in
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place, and conforming DNS servers, using SVCB does not add network
latency to connection setup.
5.1. Optimistic pre-connection and connection reuse
If an address response arrives before the corresponding SVCB
response, the client MAY initiate a connection as if the SVCB query
returned NODATA, but MUST NOT transmit any information that could be
altered by the SVCB response until it arrives. For example, a TLS
ClientHello can be altered by the "echconfig" value of a SVCB
response (Section 6.3). Clients implementing this optimization
SHOULD wait for 50 milliseconds before starting optimistic pre-
connection, as per the guidance in [HappyEyeballsV2].
An SVCB record is consistent with a connection if the client would
attempt an equivalent connection when making use of that record. If
a SVCB record is consistent with an active or in-progress connection
C, the client MAY prefer that record and use C as its connection.
For example, suppose the client receives this SVCB RRSet for a
protocol that uses TLS over TCP:
_1234._bar.example.com. 300 IN SVCB 1 svc1.example.net. (
echconfig="111..." ipv6hint=2001:db8::1 port=1234 ... )
SVCB 2 svc2.example.net. (
echconfig="222..." ipv6hint=2001:db8::2 port=1234 ... )
If the client has an in-progress TCP connection to
"[2001:db8::2]:1234", it MAY proceed with TLS on that connection
using "echconfig="222..."", even though the other record in the RRSet
has higher priority.
If none of the SVCB records are consistent with any active or in-
progress connection, clients must proceed as described in Step 3 of
the procedure in Section 3.
5.2. Generating and using incomplete responses
When following the procedure in Section 4.2, recursive resolvers MAY
terminate the procedure early and produce a reply that omits some of
the associated RRSets. This is REQUIRED when the chain length limit
is reached (Section 4.2 step 1), but might also be appropriate when
the maximum response size is reached, or when responding before fully
chasing dependencies would improve performance. When omitting
certain RRSets, recursive resolvers SHOULD prioritize information for
smaller-SvcPriority records.
As discussed in Section 3, clients MUST be able to fetch additional
information that is required to use a SVCB record, if it is not
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included in the initial response. As a performance optimization, if
some of the SVCB records in the response can be used without
requiring additional DNS queries, the client MAY prefer those
records, regardless of their priorities.
5.3. Structuring zones for performance
To avoid a delay for clients using a nonconforming recursive
resolver, domain owners SHOULD minimize the use of AliasMode records,
and choose TargetName to be a domain for which the client will have
already issued address queries (see Section 3). For
foo://foo.example.com:8080, this might look like:
; Origin zone
foo.example.com. 3600 IN CNAME foosvc.example.net.
_8080._foo.foo.example.com. 3600 IN CNAME foosvc.example.net.
; Service provider zone
foosvc.example.net. 3600 IN SVCB 1 . key65333=...
foosvc.example.net. 300 IN AAAA 2001:db8::1
Domain owners SHOULD avoid using a SvcDomainName that is below a
DNAME, as this is likely unnecessary and makes responses slower and
larger.
6. Initial SvcParamKeys
A few initial SvcParamKeys are defined here. These keys are useful
for HTTPS, and most are applicable to other protocols as well.
6.1. "alpn" and "no-default-alpn"
The "alpn" and "no-default-alpn" SvcParamKeys together indicate the
set of Application Layer Protocol Negotation (ALPN) protocol
identifiers [ALPN] and associated transport protocols supported by
this service endpoint.
As with Alt-Svc [AltSvc], the ALPN protocol identifier is used to
identify the application protocol and associated suite of protocols
supported by the endpoint (the "protocol suite"). Clients filter the
set of ALPN identifiers to match the protocol suites they support,
and this informs the underlying transport protocol used (such as
QUIC-over-UDP or TLS-over-TCP).
ALPNs are identified by their registered "Identification Sequence"
("alpn-id"), which is a sequence of 1-255 octets.
alpn-id = 1*255OCTET
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"alpn" is a multi-valued SvcParamKey. Each decoded value in the
"alpn" value list SHALL be an "alpn-id". The value list MUST NOT be
empty.
The wire format value for "alpn" consists of at least one "alpn-id"
prefixed by its length as a single octet, and these length-value
pairs are concatenated to form the SvcParamValue. These pairs MUST
exactly fill the SvcParamValue; otherwise, the SvcParamValue is
malformed.
For "no-default-alpn", the presentation and wire format values MUST
be empty.
Each scheme that uses this SvcParamKey defines a "default set" of
supported ALPNs, which SHOULD NOT be empty. To determine the set of
protocol suites supported by an endpoint (the "SVCB ALPN set"), the
client adds the default set to the list of "alpn-id"s unless the "no-
default-alpn" SvcParamKey is present. The presence of an ALPN
protocol in the SVCB ALPN set indicates that this service endpoint,
described by TargetName and the other parameters (e.g. "port") offers
service with the protocol suite associated with this ALPN protocol.
ALPN protocol names that do not uniquely identify a protocol suite
(e.g. an Identification Sequence that can be used with both TLS and
DTLS) are not compatible with this SvcParamKey and MUST NOT be
included in the SVCB ALPN set.
To establish a connection to the endpoint, clients MUST
1. Let SVCB-ALPN-Intersection be the set of protocols in the SVCB
ALPN set that the client supports.
2. Let Intersection-Transports be the set of transports (e.g. TLS,
DTLS, QUIC) implied by the protocols in SVCB-ALPN-Intersection.
3. For each transport in Intersection-Transports, construct a
ProtocolNameList containing the Identification Sequences of all
the client's supported ALPN protocols for that transport, without
regard to the SVCB ALPN set.
For example, if the SVCB ALPN set is ["http/1.1", "h3"], and the
client supports HTTP/1.1, HTTP/2, and HTTP/3, the client could
attempt to connect using TLS over TCP with a ProtocolNameList of
["http/1.1", "h2"], and could also attempt a connection using QUIC,
with a ProtocolNameList of ["h3"].
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Once the client has constructed a ClientHello, protocol negotiation
in that handshake proceeds as specified in [ALPN], without regard to
the SVCB ALPN set.
With this procedure in place, an attacker who can modify DNS and
network traffic can prevent a successful transport connection, but
cannot otherwise interfere with ALPN protocol selection. This
procedure also ensures that each ProtocolNameList includes at least
one protocol from the SVCB ALPN set.
Clients SHOULD NOT attempt connection to a service endpoint whose
SVCB ALPN set does not contain any supported protocols. To ensure
consistency of behavior, clients MAY reject the entire SVCB RRSet and
fall back to basic connection establishment if all of the RRs
indicate "no-default-alpn", even if connection could have succeeded
using a non-default alpn.
For compatibility with clients that require default transports, zone
operators SHOULD ensure that at least one RR in each RRSet supports
the default transports.
6.2. "port"
The "port" SvcParamKey defines the TCP or UDP port that should be
used to reach this alternative endpoint. If this key is not present,
clients SHALL use the authority endpoint's port number.
The presentation "value" of the SvcParamValue is a single decimal
integer between 0 and 65535 in ASCII. Any other "value" (e.g. an
empty value) is a syntax error. To enable simpler parsing, this
SvcParam MUST NOT contain escape sequences.
The wire format of the SvcParamValue is the corresponding 2 octet
numeric value in network byte order.
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.
6.3. "echconfig"
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 TargetName correspond
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to servers that have access to the corresponding private key or are
authoritative for the public name. (See Section 7.2.2 of [ECH] for
more details about the public name.) This yields an anonymity set of
cardinality equal to the number of ECH-enabled server domains
supported by a given client-facing server. Thus, even with an
encrypted ClientHello, an attacker who can enumerate the set of ECH-
enabled domains supported by a client-facing server can guess the
correct SNI with probability at least 1/K, where K is the size of
this ECH-enabled server anonymity set. This probability may be
increased via traffic analysis or other mechanisms.
6.4. "ipv4hint" and "ipv6hint"
The "ipv4hint" and "ipv6hint" keys convey IP addresses that clients
MAY use to reach the service. If A and AAAA records for TargetName
are locally available, the client SHOULD ignore these hints.
Otherwise, clients SHOULD perform A and/or AAAA queries for
TargetName as in Section 3, and clients SHOULD use the IP address in
those responses for future connections. Clients MAY opt to terminate
any connections using the addresses in hints and instead switch to
the addresses in response to the TargetName query. Failure to use A
and/or AAAA response addresses could negatively impact load balancing
or other geo-aware features and thereby degrade client performance.
Each decoded value in the value list SHALL be an IP address of the
appropriate family in standard textual format [RFC5952]. To enable
simpler parsing, this SvcParam MUST NOT contain escape sequences.
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
represents an unordered collection, and clients SHOULD pick addresses
to use in a random order. An empty list of addresses is invalid.
When selecting between IPv4 and IPv6 addresses to use, clients may
use an approach such as Happy Eyeballs [HappyEyeballsV2]. When only
"ipv4hint" is present, IPv6-only clients may synthesize IPv6
addresses as specified in [RFC7050] or ignore the "ipv4hint" key and
wait for AAAA resolution (Section 3). Recursive resolvers MUST NOT
perform DNS64 ([RFC6147]) on parameters within a SVCB record. For
best performance, server operators SHOULD include an "ipv6hint"
parameter whenever they include an "ipv4hint" parameter.
These parameters are intended to minimize additional connection
latency when a recursive resolver is not compliant with the
requirements in Section 4, and SHOULD NOT be included if most clients
are using compliant recursive resolvers. When TargetName is the
origin hostname or the owner name (which can be written as "."),
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server operators SHOULD NOT include these hints, because they are
unlikely to convey any performance benefit.
6.5. "mandatory"
In a ServiceMode RR, a SvcParamKey is considered "mandatory" if the
RR will not function correctly for clients that ignore this
SvcParamKey. Each SVCB protocol mapping SHOULD specify a set of keys
that are "automatically mandatory", i.e. mandatory if they are
present in an RR. The SvcParamKey "mandatory" is used to indicate
any mandatory keys for this RR, in addition to any automatically
mandatory keys that are present.
A ServiceMode RR is considered "compatible" with a client if the
client implements support for all its mandatory keys. If the SVCB
RRSet contains no compatible RRs, the client will generally act as if
the RRSet is empty.
In presentation format, "mandatory" contains a list of one or more
valid SvcParamKeys, either by their registered name or in the
unknown-key format (Section 2.1). Keys MAY appear in any order, but
MUST NOT appear more than once. Any listed keys MUST also appear in
the SvcParams. For example, the following is a valid list of
SvcParams:
echconfig=... key65333=ex1 key65444=ex2 mandatory=key65444,echconfig
In wire format, the keys are represented by their numeric values in
network byte order, concatenated in ascending order.
This SvcParamKey is always automatically mandatory, and MUST NOT
appear in its own value list. Other automatically mandatory keys
SHOULD NOT appear in the list either. (Including them wastes space
and otherwise has no effect.)
7. Using SVCB with HTTPS and HTTP
Use of any protocol with SVCB requires a protocol-specific mapping
specification. This section specifies the mapping for HTTPS and
HTTP.
To enable special handling for the HTTPS and HTTP use-cases, the
HTTPS RR type is defined as a SVCB-compatible RR type, specific to
the https and http schemes. Clients MUST NOT perform SVCB queries or
accept SVCB responses for "https" or "http" schemes.
The HTTPS RR wire format and presentation format are identical to
SVCB, and both share the SvcParamKey registry. SVCB semantics apply
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equally to HTTPS RRs unless specified otherwise. The presentation
format of the record is:
Name TTL IN HTTPS SvcPriority TargetName SvcParams
As with SVCB, the record is defined specifically within the Internet
("IN") Class [RFC1035].
All the SvcParamKeys defined in Section 6 are permitted for use in
HTTPS RRs. The default set of ALPN IDs is the single value
"http/1.1". The "automatically mandatory" keys (Section 6.5) are
"port", "alpn", and "no-default-alpn".
The presence of an HTTPS RR for an origin also indicates that all
HTTP resources are available over HTTPS, as discussed in Section 7.5.
This allows HTTPS RRs to apply to pre-existing "http" scheme URLs,
while ensuring that the client uses a secure and authenticated HTTPS
connection.
The HTTPS RR parallels the concepts introduced in the HTTP
Alternative Services proposed standard [AltSvc]. Clients and servers
that implement HTTPS RRs are not required to implement Alt-Svc.
7.1. Owner names for HTTPS RRs
The HTTPS RR uses Port Prefix Naming (Section 2.3), with one
modification: if the scheme is "https" and the port is 443, then the
client's original QNAME is equal to the service name (i.e. the
origin's hostname), without any prefix labels.
By removing the Attrleaf labels [Attrleaf] used in SVCB, this
construction enables offline DNSSEC signing of wildcard domains,
which are commonly used with HTTPS. Reusing the service name also
allows the targets of existing CNAME chains (e.g. CDN hosts) to
start returning HTTPS RR responses without requiring origin domains
to configure and maintain an additional delegation.
Following of HTTPS AliasMode RRs and CNAME aliases is unchanged from
SVCB.
Clients always convert "http" URLs to "https" before performing an
HTTPS RR query using the process described in Section 7.5, so domain
owners MUST NOT publish HTTPS RRs with a prefix of "_http".
Note that none of these forms alter the HTTPS origin or authority.
For example, clients MUST continue to validate TLS certificate
hostnames based on the origin.
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7.2. Relationship to Alt-Svc
Publishing a ServiceMode HTTPS RR in DNS is intended to be similar to
transmitting an Alt-Svc field value over HTTPS, and receiving an
HTTPS RR is intended to be similar to receiving that field value over
HTTPS. However, there are some differences in the intended client
and server behavior.
7.2.1. ALPN usage
Unlike Alt-Svc Field Values, HTTPS RRs can contain multiple ALPN IDs,
and clients are encouraged to offer additional ALPNs that they
support (subject to security constraints).
TO BE REMOVED: The ALPN semantics in [AltSvc] are ambiguous, and
problematic in some interpretations. We should update [AltSvc] to
give it well-defined semantics that match HTTPS RRs.
7.2.2. Untrusted channel
SVCB does not require or provide any assurance of authenticity.
(DNSSEC signing and verification, which would provide such assurance,
are OPTIONAL.) The DNS resolution process is treated as an untrusted
channel that learns only the QNAME, and is prevented from mounting
any attack beyond denial of service.
Alt-Svc parameters that cannot be safely received in this model MUST
NOT have a corresponding defined SvcParamKey. For example, there is
no SvcParamKey corresponding to the Alt-Svc "persist" parameter,
because this parameter is not safe to accept over an untrusted
channel.
7.2.3. TTL and granularity
There is no SvcParamKey corresponding to the Alt-Svc "ma" (max age)
parameter. Instead, server operators encode the expiration time in
the DNS TTL.
The appropriate TTL value will typically be similar to the "ma" value
used for Alt-Svc, but may vary depending on the desired efficiency
and agility. Some DNS caches incorrectly extend the lifetime of DNS
records beyond the stated TTL, so server operators cannot rely on
HTTPS RRs expiring on time. Shortening the TTL to compensate for
incorrect caching is NOT RECOMMENDED, as this practice impairs the
performance of correctly functioning caches and does not guarantee
faster expiration from incorrect caches. Instead, server operators
SHOULD maintain compatibility with expired records until they observe
that nearly all connections have migrated to the new configuration.
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Sending Alt-Svc over HTTP allows the server to tailor the Alt-Svc
Field Value specifically to the client. When using an HTTPS RR,
groups of clients will necessarily receive the same SvcParams.
Therefore, HTTPS RRs are not suitable for uses that require single-
client granularity.
7.3. Interaction with Alt-Svc
Clients that do not implement support for Encrypted ClientHello MAY
skip the HTTPS RR query if a usable Alt-Svc value is available in the
local cache. If Alt-Svc connection fails, these clients SHOULD fall
back to the HTTPS RR client connection procedure (Section 3).
For clients that implement support for ECH, the interaction between
HTTPS RRs and Alt-Svc is described in Section 8.1.
This specification does not alter the DNS queries performed when
connecting to an Alt-Svc hostname (typically A and/or AAAA only).
7.4. Requiring Server Name Indication
Clients MUST NOT use an HTTPS RR 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 TargetName.
7.5. HTTP Strict Transport Security
By publishing a usable HTTPS RR, the server operator indicates that
all useful HTTP resources on that origin are reachable over HTTPS,
similar to HTTP Strict Transport Security [HSTS].
Prior to making an "http" scheme request, the client SHOULD perform a
lookup to determine if any HTTPS RRs exist for that origin. To do
so, the client SHOULD construct a corresponding "https" URL as
follows:
1. Replace the "http" scheme with "https".
2. If the "http" URL explicitly specifies port 80, specify port 443.
3. Do not alter any other aspect of the URL.
This construction is equivalent to Section 8.3 of [HSTS], point 5.
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If an HTTPS RR query for this "https" URL returns any AliasMode HTTPS
RRs, or any compatible ServiceMode HTTPS RRs (see Section 6.5), the
client SHOULD act as if it has received an HTTP "307 Temporary
Redirect" redirect to this "https" URL. (Receipt of an incompatible
ServiceMode RR does not trigger the redirect behavior.) Because
HTTPS RRs are received over an often insecure channel (DNS), clients
MUST NOT place any more trust in this signal than if they had
received a 307 redirect over cleartext HTTP.
When making an "https" scheme request to an origin with an HTTPS RR,
either directly or via the above redirect, the client SHOULD
terminate the connection if there are any errors with the underlying
secure transport, such as errors in certificate validation. This
aligns with Section 8.4 and Section 12.1 of [HSTS].
7.6. HTTP-based protocols
We define an "HTTP-based protocol" as one that involves connecting to
an "http:" or "https:" URL. When implementing an HTTP-based
protocol, clients that use HTTPS RRs for HTTP SHOULD also use it for
this URL. For example, clients that support HTTPS RRs and implement
the altered WebSocket [WebSocket] opening handshake from the W3C
Fetch specification [FETCH] SHOULD use HTTPS RRs for the
"requestURL".
An HTTP-based protocol MAY define its own SVCB mapping. Such
mappings MAY be defined to take precedence over HTTPS RRs.
8. SVCB/HTTPS RR parameter for ECH configuration
The SVCB "echconfig" parameter is defined for conveying the ECH
configuration of an alternative endpoint. In wire format, the value
of the parameter is an ECHConfigs vector [ECH], including the
redundant length prefix. In presentation format, the value is a
single ECHConfigs encoded in Base64 [base64]. Base64 is used here to
simplify integration with TLS server software. To enable simpler
parsing, this SvcParam MUST NOT contain escape sequences.
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 desired
service.
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8.1. Client behavior
The general client behavior specified in Section 3 permits clients to
retry connection with a less preferred alternative if the preferred
option fails, including falling back to a direct connection if all
SVCB options fail. This behavior is not suitable for ECH, because
fallback would negate the privacy benefits of ECH. Accordingly, ECH-
capable clients SHALL implement the following behavior for connection
establishment:
1. Perform connection establishment using HTTPS RRs as described in
Section 3, but do not fall back to address records (steps 5 and
6). If there are compatible HTTPS RRs, they all have an
"echconfig" key, and attempts to connect to them all fail,
terminate connection establishment.
2. If the client implements Alt-Svc, try to connect using any
entries from the Alt-Svc cache.
3. Fall back to address records (steps 5 and 6 of Section 3) if
necessary.
As a latency optimization, clients MAY prefetch DNS records for later
steps before they are needed.
8.2. Deployment considerations
An HTTPS RRSet containing some RRs with "echconfig" and some without
is vulnerable to a downgrade attack. This configuration is NOT
RECOMMENDED. Zone owners who do use such a mixed configuration
SHOULD mark the RRs with "echconfig" as more preferred (i.e. smaller
SvcPriority) than those without, in order to maximize the likelihood
that ECH will be used in the absence of an active adversary.
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 HTTPS 1 . alpn=h3 ...
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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 HTTPS RRs, the owner of aliased.example could alias the apex by
adding one additional record:
@ 7200 IN HTTPS 0 pool.svc.example.
With this record in place, HTTPS-RR-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-HTTPS-RR-aware
clients will just ignore the new record.
Similar to CNAME, HTTPS RRs have 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 HTTPS 1 h3pool alpn=h2,h3 echconfig="123..."
HTTPS 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 HTTPS RRs or not. If the client
does support HTTPS RRs, all connections will be upgraded to HTTPS,
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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
[Attrleaf] will be used. For example, to reach an example resource
of "baz://api.example.com:8765", the following SVCB record would be
used to alias it to "svc4-baz.example.net." which in-turn could
return AAAA/A records and/or SVCB records in ServiceMode:
_8765._baz.api.example.com. 7200 IN SVCB 0 svc4-baz.example.net.
HTTPS RRs use similar Attrleaf labels if the origin contains a non-
default port.
10. Interaction with other standards
This standard is intended to reduce connection latency and improve
user privacy. Server operators implementing this standard SHOULD
also implement TLS 1.3 [RFC8446] and OCSP Stapling [RFC6066], both of
which confer substantial performance and privacy benefits when used
in combination with SVCB records.
To realize the greatest privacy benefits, this proposal is intended
for use over a privacy-preserving DNS transport (like DNS over TLS
[DoT] or DNS over HTTPS [DoH]). However, performance improvements,
and some modest privacy improvements, are possible without the use of
those standards.
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
Global Scoped Entry Registry [Attrleaf]. The scheme SHOULD have an
entry in the IANA URI Schemes Registry [RFC7595]. The scheme SHOULD
have a defined specification for use with SVCB.
11. Security Considerations
SVCB/HTTPS RRs are intended for distribution over untrusted channels,
and clients are REQUIRED to verify that the alternative endpoint is
authoritative for the service (similar to Section 2.1 of [AltSvc]).
Therefore, DNSSEC signing and validation are OPTIONAL for publishing
and using SVCB and HTTPS RRs.
Clients MUST ensure that their DNS cache is partitioned for each
local network, or flushed on network changes, to prevent a local
adversary in one network from implanting a forged DNS record that
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allows them to track users or hinder their connections after they
leave that network.
An attacker who can prevent SVCB resolution can deny clients any
associated security benefits. A hostile recursive resolver can
always deny service to SVCB queries, but network intermediaries can
often prevent resolution as well, even when the client and recursive
resolver validate DNSSEC and use a secure transport. These downgrade
attacks can prevent the HTTPS upgrade provided by the HTTPS RR
(Section 7.5), and disable the encryption enabled by the echconfig
SvcParamKey (Section 8). To prevent downgrades, Section 3.1
recommends that clients abandon the connection attempt when such an
attack is detected.
A hostile DNS intermediary might forge AliasForm "." records
(Section 2.5.1) as a way to block clients from accessing particular
services. Such an adversary could already block entire domains by
forging erroneous responses, but this mechanism allows them to target
particular protocols or ports within a domain. Clients that might be
subject to such attacks SHOULD ignore AliasForm "." records.
12. IANA Considerations
12.1. SVCB RRType
This document defines a new DNS RR type, SVCB, whose value 64 has
been allocated by IANA from the "Resource Record (RR) TYPEs"
subregistry of the "Domain Name System (DNS) Parameters" registry:
Type: SVCB
Value: 64
Meaning: General Purpose Service Endpoints
Reference: This document
12.2. HTTPS RRType
This document defines a new DNS RR type, HTTPS, whose value 65 has
been allocated by IANA from the "Resource Record (RR) TYPEs"
subregistry of the "Domain Name System (DNS) Parameters" registry:
Type: HTTPS
Value: 65
Meaning: HTTPS Specific Service Endpoints
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Reference: This document
12.3. New registry for Service Parameters
The "Service Binding (SVCB) Parameter Registry" defines the namespace
for parameters, including string representations and numeric
SvcParamKey values. This registry is shared with other SVCB-
compatible RR types, such as the HTTPS RR.
ACTION: create and include a reference to this registry.
12.3.1. Procedure
A registration MUST include the following fields:
o Number: SvcParamKey wire format numeric identifier (range 0-65535)
o Name: SvcParamKey presentation name
o Meaning: a short description
o Pointer to specification text
SvcParamKey entries to be added to this namespace have different
policies ([RFC5226], Section 4.1) based on their range:
+-------------+-------------------------+
| Number | IANA Policy |
+-------------+-------------------------+
| 0-255 | Standards Action |
| | |
| 256-32767 | Expert Review |
| | |
| 32768-65280 | First Come First Served |
| | |
| 65280-65534 | Private Use |
| | |
| 65535 | Standards Action |
+-------------+-------------------------+
Apart from the initial contents, the SvcParamKey name MUST NOT start
with "key".
12.3.2. Initial contents
The "Service Binding (SVCB) Parameter Registry" shall initially be
populated with the registrations below:
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+-------------+-----------------+----------------------+------------+
| Number | Name | Meaning | Reference |
+-------------+-----------------+----------------------+------------+
| 0 | mandatory | Mandatory keys in | (This |
| | | this RR | document) |
| | | | |
| 1 | alpn | Additional supported | (This |
| | | protocols | document) |
| | | | |
| 2 | no-default-alpn | No support for | (This |
| | | default protocol | document) |
| | | | |
| 3 | port | Port for alternative | (This |
| | | endpoint | document) |
| | | | |
| 4 | ipv4hint | IPv4 address hints | (This |
| | | | document) |
| | | | |
| 5 | echconfig | Encrypted | (This |
| | | ClientHello info | document) |
| | | | |
| 6 | ipv6hint | IPv6 address hints | (This |
| | | | document) |
| | | | |
| 65280-65534 | keyNNNNN | Private Use | (This |
| | | | document) |
| | | | |
| 65535 | key65535 | Reserved ("Invalid | (This |
| | | key") | document) |
+-------------+-----------------+----------------------+------------+
TODO: do we also want to reserve a range for greasing?
12.4. Registry updates
Per [RFC6895], please add the following entries to the data type
range of the Resource Record (RR) TYPEs registry:
+-------+------------------------------------------+----------------+
| TYPE | Meaning | Reference |
+-------+------------------------------------------+----------------+
| SVCB | Service Location and Parameter Binding | (This |
| | | document) |
| | | |
| HTTPS | HTTPS Service Location and Parameter | (This |
| | Binding | document) |
+-------+------------------------------------------+----------------+
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Per [Attrleaf], please add the following entry to the DNS Underscore
Global Scoped Entry Registry:
+---------+------------+-----------------+-----------------+
| RR TYPE | _NODE NAME | Meaning | Reference |
+---------+------------+-----------------+-----------------+
| HTTPS | _https | HTTPS SVCB info | (This document) |
+---------+------------+-----------------+-----------------+
13. Acknowledgments and Related Proposals
There have been a wide range of proposed solutions over the years to
the "CNAME at the Zone Apex" challenge proposed. These include
[I-D.bellis-dnsop-http-record], [I-D.ietf-dnsop-aname], and others.
Thank you to Ian Swett, Ralf Weber, Jon Reed, Martin Thomson, Lucas
Pardue, Ilari Liusvaara, Tim Wicinski, Tommy Pauly, Chris Wood, David
Benjamin, and others for their feedback and suggestions on this
draft.
14. References
14.1. Normative References
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[Attrleaf]
Crocker, D., "Scoped Interpretation of DNS Resource
Records through "Underscored" Naming of Attribute Leaves",
BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
<https://www.rfc-editor.org/info/rfc8552>.
[base64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[DNAME] Rose, S. and W. Wijngaards, "DNAME Redirection in the
DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
<https://www.rfc-editor.org/info/rfc6672>.
[DoH] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
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[DoT] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[ECH] Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
Encrypted Client Hello", draft-ietf-tls-esni-07 (work in
progress), June 2020.
[HappyEyeballsV2]
Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/info/rfc8305>.
[HSTS] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797,
DOI 10.17487/RFC6797, November 2012,
<https://www.rfc-editor.org/info/rfc6797>.
[HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", draft-ietf-quic-http-29 (work in progress),
June 2020.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928,
DOI 10.17487/RFC1928, March 1996,
<https://www.rfc-editor.org/info/rfc1928>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, DOI 10.17487/RFC3225, December 2001,
<https://www.rfc-editor.org/info/rfc3225>.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
2003, <https://www.rfc-editor.org/info/rfc3597>.
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[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35,
RFC 7595, DOI 10.17487/RFC7595, June 2015,
<https://www.rfc-editor.org/info/rfc7595>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
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[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
Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[DNSTerm] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[FETCH] "Fetch Living Standard", May 2020,
<https://fetch.spec.whatwg.org/>.
[I-D.bellis-dnsop-http-record]
Bellis, R., "A DNS Resource Record for HTTP", draft-
bellis-dnsop-http-record-00 (work in progress), November
2018.
[I-D.ietf-dnsop-aname]
Finch, T., Hunt, E., Dijk, P., Eden, A., and W. Mekking,
"Address-specific DNS aliases (ANAME)", draft-ietf-dnsop-
aname-04 (work in progress), July 2019.
[I-D.tapril-ns2]
April, T., "Parameterized Nameserver Delegation with NS2
and NS2T", draft-tapril-ns2-00 (work in progress), March
2020.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <https://www.rfc-editor.org/info/rfc6895>.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<https://www.rfc-editor.org/info/rfc2782>.
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[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
14.3. URIs
[1] https://github.com/MikeBishop/dns-alt-svc
Appendix A. Decoding text in zone files
DNS zone files are capable of representing arbitrary octet sequences
in basic ASCII text, using various delimiters and encodings. The
algorithm for decoding these character-strings is defined in
Section 5.1 of [RFC1035]. Here we summarize the allowed input to
that algorithm, using ABNF:
; non-special is VCHAR minus DQUOTE, ";", "(", ")", and "\".
non-special = %x21 / %x23-27 / %x2A-3A / %x3C-5B / %x5D-7E
; non-digit is VCHAR minus DIGIT
non-digit = %x21-2F / %x3A-7E
; dec-octet is a number 0-255 as a three-digit decimal number.
dec-octet = ( "0" / "1" ) 2DIGIT /
"2" ( ( %x30-34 DIGIT ) / ( "5" %x30-35 ) )
escaped = "\" ( non-digit / dec-octet )
contiguous = 1*( non-special / escaped )
quoted = DQUOTE *( contiguous / ( ["\"] WSP ) ) DQUOTE
char-string = contiguous / quoted
The decoding algorithm allows "char-string" to represent any
"*OCTET". In this document, this algorithm is referred to as
"character-string decoding". The algorithm is the same as used by
"<character-string>" in RFC 1035, although the output length in this
document is not limited to 255 octets.
A.1. Decoding a value list
In order to represent lists of values in zone files, this
specification uses an extended version of character-string decoding
that adds the use of "," as a delimiter after double-quote
processing. When "," is not escaped (by a preceding "\" or as the
escape sequence "\044"), it separates values in the output, which is
a list of 1*OCTET. (For simplicity, empty values are not allowed.)
We refer to this modified procedure as "value-list decoding".
value-list = char-string
list-value = 1*OCTET
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For example, consider these "char-string" SvcParamValues:
"part1,part2\,part3"
part1,part2\044part3
Character-string decoding either of these inputs would produce a
single "*OCTET" output:
part1,part2,part3
Value-list decoding either of these inputs would instead convert it
to a list of two "list-value"s:
part1
part2,part3
Appendix B. Comparison with alternatives
The SVCB and HTTPS RR types closely resemble, and are inspired by,
some existing record types and proposals. A complaint with all of
the alternatives is that web clients have seemed unenthusiastic about
implementing them. The hope here is that by providing an extensible
solution that solves multiple problems we will overcome the inertia
and have a path to achieve client implementation.
B.1. Differences from the SRV RR type
An SRV record [SRV] can perform a similar function to the SVCB
record, informing a client to look in a different location for a
service. However, there are several differences:
o SRV records are typically mandatory, whereas clients will always
continue to function correctly without making use of SVCB.
o SRV records cannot instruct the client to switch or upgrade
protocols, whereas SVCB can signal such an upgrade (e.g. to
HTTP/2).
o SRV records are not extensible, whereas SVCB and HTTPS RRs can be
extended with new parameters.
o SVCB records use 16 bit for SvcPriority for consistency with SRV
and other RR types that also use 16 bit priorities.
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B.2. Differences from the proposed HTTP record
Unlike [I-D.bellis-dnsop-http-record], this approach is extensible to
cover Alt-Svc and Encrypted ClientHello use-cases. Like that
proposal, this addresses the zone apex CNAME challenge.
Like that proposal, it remains necessary to continue to include
address records at the zone apex for legacy clients.
B.3. Differences from the proposed ANAME record
Unlike [I-D.ietf-dnsop-aname], this approach is extensible to cover
Alt-Svc and ECH use-cases. This approach also does not require any
changes or special handling on either authoritative or primary
servers, beyond optionally returning in-bailiwick additional records.
Like that proposal, this addresses the zone apex CNAME challenge for
clients that implement this.
However, with this SVCB proposal, it remains necessary to continue to
include address records at the zone apex for legacy clients. If
deployment of this standard is successful, the number of legacy
clients will fall over time. As the number of legacy clients
declines, the operational effort required to serve these users
without the benefit of SVCB indirection should fall. Server
operators can easily observe how much traffic reaches this legacy
endpoint, and may remove the apex's address records if the observed
legacy traffic has fallen to negligible levels.
B.4. Comparison with separate RR types for AliasMode and ServiceMode
Abstractly, functions of AliasMode and ServiceMode are independent,
so it might be tempting to specify them as separate RR types.
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 ServiceMode query, emit both a
ServiceMode and an AliasMode 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.
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Appendix C. Change history
o draft-ietf-dnsop-svcb-https-01
* Added a "mandatory" SvcParamKey
* Added the ability to indicate that a service does not exist
* Adjusted resolution and ALPN algorithms
* Major terminology revisions for "origin" and CamelCase names
* Revised ABNF
* Include allocated RR type numbers
* Various corrections, explanations, and recommendations
o draft-ietf-dnsop-svcb-https-00
* Rename HTTPSSVC RR to HTTPS RR
* Rename "an SVCB" to "a SVCB"
* Removed "design considerations and open issues" section and
some other "to be removed" text
o draft-ietf-dnsop-svcb-httpssvc-03
* Revised chain length limit requirements
* Revised IANA registry rules for SvcParamKeys
* Require HTTPS clients to implement SNI
* Update terminology for Encrypted ClientHello
* Clarifications: non-default ports, transport proxies, HSTS
procedure, WebSocket behavior, wire format, IP hints, inner/
outer ClientHello with ECH
* Various textual and ABNF corrections
o draft-ietf-dnsop-svcb-httpssvc-02
* All changes to Alt-Svc have been removed
* Expanded and reorganized examples
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Internet-Draft SVCB and HTTPS RRs for DNS July 2020
* 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
o 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.
o draft-ietf-dnsop-svcb-httpssvc-00
* Document an optimization for optimistic pre-connection. (Chris
Wood)
* Relax IP hint handling requirements. (Eric Rescorla)
o draft-nygren-dnsop-svcb-httpssvc-00
* Generalize to an SVCB record, with special-case handling for
Alt-Svc and HTTPS separated out to dedicated sections.
* Split out a separate HTTPSSVC record for the HTTPS use-case.
* Remove the explicit SvcRecordType=0/1 and instead make the
AliasForm vs ServiceForm be implicit. This was based on
feedback recommending against subtyping RR type.
* Remove one optimization.
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Internet-Draft SVCB and HTTPS RRs for DNS July 2020
o draft-nygren-httpbis-httpssvc-03
* Change redirect type for HSTS-style behavior from 302 to 307 to
reduce ambiguities.
o draft-nygren-httpbis-httpssvc-02
* Remove the redundant length fields from the wire format.
* Define a SvcDomainName of "." for SvcRecordType=1 as being the
HTTPSSVC RRNAME.
* Replace "hq" with "h3".
o draft-nygren-httpbis-httpssvc-01
* Fixes of record name. Replace references to "HTTPSVC" with
"HTTPSSVC".
o draft-nygren-httpbis-httpssvc-00
* Initial version
Authors' Addresses
Ben Schwartz
Google
Email: bemasc@google.com
Mike Bishop
Akamai Technologies
Email: mbishop@evequefou.be
Erik Nygren
Akamai Technologies
Email: erik+ietf@nygren.org
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