Service binding and parameter specification via the DNS (DNS SVCB and HTTPSSVC)Googlebemasc@google.comAkamai Technologiesmbishop@evequefou.beAkamai Technologieserik+ietf@nygren.org
General
DNSOP Working GroupInternet-DraftThis document specifies the “SVCB” and “HTTPSSVC” DNS resource record types to
facilitate the lookup of information needed to make connections for
origin resources, such as for HTTPS URLs. SVCB records
allow an origin to be served from multiple network
locations, each with associated parameters (such as transport protocol
configuration and keying material for encrypting TLS SNI). They also
enable aliasing of apex domains, which is not possible with CNAME.
The HTTPSSVC DNS 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: The specific name for this RR type is an open
topic for discussion. “SVCB” and “HTTPSSVC” are meant as placeholders
as they are easy to replace. Other names might include “B”,
“SRV2”, “SVCHTTPS”, “HTTPS”, and “ALTSVC”.The SVCB and HTTPSSVC RRs provide clients with complete instructions
for access to an origin. 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 ).
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-trip and lookups required to
learn this additional information.The SVCB and HTTPSSVC RRs also help when the operator of an origin
wishes to delegate operational control to one or more other domains, e.g.
delegating the origin resource “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.
As HTTPS is a primary use-case and has special requirements,
the HTTPSSVC RR is also defined within this document as a special case
of SVCB.
Services wishing to avoid the need for an label with
SVCB may follow the pattern of HTTPSSVC and assign their own
SVCB-compatible RR types.All behaviors described as applying to the SVCB RR also apply
to the HTTPSSVC RR unless explicitly stated otherwise.
describes additional behaviors
specific to the HTTPSSVC record. Apart from
and introductory examples, much of this document refers only to the SVCB RR,
but those references should be taken to apply to SVCB, HTTPSSVC,
and any future SVCB-compatible RR types.The SVCB RR has two forms: 1) the “Alias Form” simply delegates operational
control for a resource; 2) the “Service Form” binds together
configuration information for a service endpoint.
The Service Form 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 HTTPSSVC.TO BE REMOVED: Another open question is whether SVCB records
should be self-descriptive and include the service name
(eg, “https”) in the RDATA section to avoid ambiguity.
Perhaps this could be included as a svc=”baz” parameter
for protocols that are not the default for the RR type?
Current inclination is to not do so.As an introductory example for an HTTPS origin resource, a set of
example HTTPSSVC and associated A+AAAA records might be:In the preceding example, both of the “example.com” and
“www.example.com” origin names are aliased to use alternative service
endpoints offered as “svc.example.net” (with “www.example.com”
continuing to use a CNAME alias). HTTP/2 is available on a cluster of
machines located at svc2.example.net with TCP port 8002 and HTTP/3 is
available on a cluster of machines located at svc3.example.net with
UDP port 8003. The client can use the specified ESNI keys to encrypt
the SNI values of “example.com” and “www.example.com” in the handshake
with these alternative service endpoints. When connecting, clients will
continue to treat the authoritative origins as “https://example.com”
and “https://www.example.com”, respectively.For services other than HTTPS (as well as for HTTPS origins
with non-default ports), the SVCB RR and an 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.The goal of the SVCB RR is to allow clients to resolve a single
additional DNS RR in a way that:Provides service endpoints authoritative for the service,
along with parameters associated with each of these endpoints.Does not assume that all alternative service 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.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 HTTPSSVC and the HTTPS use-case include:Connect directly to (QUIC transport)
alternative service endpointsObtain the keys associated with an alternative service endpointSupport non-default TCP and UDP portsAddress a set of long-standing issues due to HTTP(S) clients not
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 is the case for zone apex names)Provide an HSTS-like indication signaling
for the duration of the DNS RR TTL that the HTTPS scheme should
be used instead of HTTP (see ).This subsection briefly describes the SVCB RR in
a non-normative manner. (As mentioned above, this all
applies equally to the HTTPSSVC RR which shares
the same encoding, format, and high-level semantics.)The SVCB RR has two forms: AliasForm and ServiceForm.
SVCB RR entries with two non-empty fields are in AliasForm.
When more fields are present, this indicates that the SVCB RR
is in ServiceForm. The fields are:SvcFieldPriority: The priority of this record (relative to others,
with lower values preferred). Applicable for the ServiceForm,
and otherwise has value “0”. (Described in .)SvcDomainName: The domain name of either the alias target (for
AliasForm) or the alternative service endpoint (for ServiceForm).SvcFieldValue: A list of key=value pairs
describing the alternative service endpoint for the domain name specified in
SvcDomainName (only for ServiceForm and otherwise empty).
Described in .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 must 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 may attach in-bailiwick SVCB, A, AAAA, and CNAME
records in the Additional Section to responses for an SVCB query.When in the ServiceForm, the SvcFieldValue of the SVCB RR
provides an extensible data model for describing network
endpoints that are authoritative for the origin, along with
parameters associated with each of these endpoints.For the HTTPS use-case with the HTTPSSVC RR, there is also direct mapping
from the SvcDomainName and SvcFieldValue into
HTTP Alternative Services (Alt-Svc) entries .
Encoding this information here enables many of the benefits of Alt-Svc,
without waiting for a full HTTP connection 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.This document also defines a parameter for Encrypted SNI
keys, both as a general SVCB parameter and also as a corresponding
Alt-Svc parameter. See .For consistency with , we adopt the following definitions:An “origin” is an information source as in .
For services other than HTTPS, the exact definition will
need to be provided by the document mapping that service
onto the SVCB RR.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 Alt-Svc.An “alternative service” is a different server that can serve the
origin over a specified protocol.For example within HTTPS, the origin consists of a scheme (typically
“https”), a host name, and a port (typically “443”).Additional DNS terminology intends to be consistent
with .SVCB is a contraction of “service binding”. HTTPSSVC is a contraction of
“HTTPS service”. SVCB, HTTPSSVC, 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 when, and only when, they
appear in all capitals, as shown here.The SVCB DNS resource record (RR) type (RR type ???)
is used to locate endpoints that can service an origin.
There is special handling for the case of “https” origins.
The presentation format of the record is:The SVCB record is defined specifically within
the Internet (“IN”) Class ().
SvcFieldPriority is a number in the range 0-65535,
SvcDomainName is a domain name,
and SvcFieldValue is a set of key=value pairs present for the ServiceForm.
The SvcFieldValue is empty for the AliasForm.The algorithm for resolving SVCB records and associated
address records is specified in .In ServiceForm, the SvcFieldValue contains key=value pairs.
Keys are IANA-registered SvcParamKeys ()
with both a case-insensitive string representation and
a numeric representation in the range 0-65535.
Registered key names should only contain characters from the ranges
“a”-“z”, “0”-“9”, and “-“. In ABNF ,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 SVCB format preserves the order of values and can encode multiple
values for the same parameter. However, clients MUST consider only
the first appearance of a parameter unless its specification explicitly allows
multiple values.The presentation format for SvcFieldValue is a whitespace-separated
list of the key=value pairs. Each pair is presented in the following form:The value format is intended to match the definition of <character-string>
in Section 5.1. (Unlike <character-string>, the length
of a value is not limited to 255 characters.)Unrecognized keys are represented in presentation
format as “keyNNNNN” where NNNNN is the numeric
value of the key type without leading zeros.
In presentation format, values of unrecognized keys
should be represented in wire format, using decimal escape codes
(e.g. \255) when necessary.The RDATA for the SVCB RR consists of:a 2 octet field for SvcFieldPriority as an integer in network
byte order. For AliasForm, SvcFieldPriority MUST be 0.the uncompressed SvcDomainName, represented as
a sequence of length-prefixed labels as in Section 3.1 of .the SvcFieldValue byte string, consuming the remainder of the record
(so smaller than 65535 octets and constrained by the RDATA
and DNS message sizes).AliasForm is defined by SvcFieldValue being empty.When SvcFieldValue is non-empty (ServiceForm), it contains a list of
SvcParamKey=SvcParamValue pairs with length-prefixes for the SvcParamValues,
each of which contains:a 2 octet field containing the SvcParamKey as an
integer in network byte order.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).an octet string of the length defined by the previous field.If the parser reaches the end of the RDATA while parsing a SvcFieldValue,
the RR is invalid and MUST be discarded.TODO: decide if we want special handling for any SvcParamKey ranges?
For example: range for greasing; experimental range;
range-of-mandatory-to-use-the-RR vs range of
ignore-just-param-if-unknown.When querying the SVCB RR, an origin is typically translated into a QNAME
by prefixing the port and scheme with “_”, then concatenating them with the
host name, resulting in a domain name like “_8004._examplescheme.api.example.com.”.Protocol mappings for SVCB MAY remove the port or replace it with other
protocol-specific information, but MUST retain the scheme in the QNAME.
RR types other than SVCB can define additional behavior for translating
origins to QNAMEs. See for the HTTPSSVC behavior.When a prior CNAME or SVCB record has aliased to
an 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, clients MUST continue to validate TLS certificate
hostnames based on the origin host.As an example:would indicate that “foo://api.example.com:8443” is aliased
to use ALPN protocol “bar” service endpoints offered at “svc4.example.net”
on port 8004.The SvcRecordType is implicit based on the presence of SvcFieldValue,
and defines the form of the SVCB RR.
When SvcFieldValue is empty, the SVCB SvcRecordType is defined to be
in AliasForm. Otherwise, the SVCB SvcRecordType is defined to be
in ServiceForm.Within an SVCB RRSet,
all RRs should have the same SvcRecordType.
If an RRSet contains a record in AliasForm, the client MUST ignore
any records in the set with ServiceForm.When SvcRecordType is AliasForm, the SVCB record is to be treated
similar to a CNAME alias pointing to
SvcDomainName. SVCB RRSets SHOULD only have a single resource
record in this form. If multiple are present, clients or recursive
resolvers SHOULD pick one at random.The AliasForm’s primary purpose is to allow aliasing
at the zone apex, where CNAME is not allowed.
For example, if an operator of https://example.com wanted to
point HTTPS requests to a service operating at svc.example.net,
they would publish a record such as:The SvcDomainName MUST point to a domain name that contains
another SVCB record, address (AAAA and/or A) records,
or both address records and a ServiceForm SVCB record.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
record. Clients and recursive resolvers MUST follow CNAMEs as normal.Due to the risk of loops, clients and recursive resolvers MUST
implement loop detection. Chains of consecutive SVCB and CNAME
records SHOULD be limited to (8?) prior to reaching terminal address
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.Note that SVCB AliasForm RRs do not alias to RR types other than
address records (AAAA and A), CNAMEs, and ServiceForm SVCB records.
For example, an AliasForm SVCB record does not alias to an HTTPSSVC record,
nor vice-versa.When SvcRecordType is the ServiceForm, the combination of
SvcDomainName and SvcFieldValue parameters within each resource record
associates an alternative service location with its connection parameters. defines a direct mapping between Alt-Svc () values
and the SVCB ServiceForm. Protocols using SVCB may use this Alt-Svc
mapping or specify their own semantics. Unless specified otherwise by the
protocol mapping, clients MUST ignore SvcFieldValue parameters that they do
not recognize.For ServiceForm SVCB RRs, if SvcDomainName has the value “.”, then the
owner name of this record MUST be used as the effective
SvcDomainName. (The SvcDomainName of an SVCB RR in AliasForm MUST NOT have
this value.)For example, in the following example “svc2.example.net”
is the effective SvcDomainName:As RRs within an RRSet are explicitly unordered collections, the
SvcFieldPriority value serves to indicate priority.
SVCB RRs with a smaller SvcFieldPriority value SHOULD be given
preference over RRs with a larger SvcFieldPriority value.When receiving an RRSet containing multiple SVCB records with the
same SvcFieldPriority value, clients SHOULD apply a random shuffle within a
priority level to the records before using them, to ensure uniform
load-balancing.An SVCB-aware client resolves an origin HOST by attempting to determine
the preferred SvcFieldValue and IP addresses for its service, using the
following procedure:Issue parallel AAAA/A and SVCB queries for the name HOST.
The answers for these may or may not include CNAME pointers
before reaching one or more of these records.If an SVCB record of AliasForm SvcRecordType is returned for HOST,
clients MUST loop back to step 1 replacing HOST with SvcDomainName,
subject to loop detection heuristics.If one or more SVCB records of ServiceForm SvcRecordType are returned
for HOST, clients should select the highest-priority option with
acceptable parameters, and resolve AAAA and/or A records for its
SvcDomainName if they are not already available. These are the
preferred SvcFieldValue and IP addresses. If the connection fails, the
client MAY try to connect using values from a lower-priority record.
If none of the options succeed, the client SHOULD connect to the origin
server directly.If an SVCB record for HOST does not exist, the received AAAA and/or A
records are the preferred IP addresses and there is no SvcFieldValue.This procedure does not rely on any recursive or authoritative 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 .Some important optimizations are discussed in
to avoid additional latency in comparison to ordinary AAAA/A lookups.Clients using a domain-oriented transport proxy like HTTP CONNECT
( Section 4.3.6) or SOCKS5 () SHOULD disable
SVCB support if performing SVCB queries would violate the
client’s privacy intent.If the client can safely perform SVCB queries (e.g. via the
proxy or an affiliated resolver), the client SHOULD follow
the standard SVCB resolution process, selecting the highest priority
option that is compatible with the client and the proxy. The client
SHOULD provide the final SvcDomainName and port (if present) to the
proxy as the destination host and port.Providing the proxy with the final SvcDomainName has several benefits:It allows the client to use the SvcFieldValue, if present, which is
only usable with a specific SvcDomainName. The SvcFieldValue may
include information that enhances performance (e.g. alpn) and privacy
(e.g. esnikeys).It allows the origin to delegate the apex domain.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.When replying to an SVCB query, authoritative DNS servers SHOULD return
A, AAAA, and SVCB records (as
well as any relevant CNAME records) in the Additional Section for any
in-bailiwick SvcDomainNames.Recursive resolvers that are aware of SVCB SHOULD ensure that the client can
execute the procedure in without issuing a second
round of queries, by following this procedure while constructing a response
to a stub resolver for an SVCB record query:When processing an SVCB response from an authoritative server, add it to
the Additional section (unless it is the Answer).Inspect whether each record is in AliasForm or ServiceForm.
If at least one record is in AliasForm, ignore all other SVCB records in the
RRSet.If the record is in AliasForm, resolve A, AAAA, and SVCB records for
the SvcDomainName. If the SVCB record does not exist, add the A and AAAA
records to the Additional section. Otherwise, go to step 1,
subject to loop detection heuristics.If the records are in ServiceForm, resolve A and AAAA records for each
SvcDomainName (or for the owner name if the SvcDomainName is “.”), and include all
the results in the Additional section.All DNS servers SHOULD treat the SvcParam portion of the SVCB RR
as opaque and SHOULD NOT try to alter their behavior based
on its contents.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 an SVCB response SHOULD be placed
in cache before performing any followup queries.
With these optimizations in place, and conforming DNS servers,
using SVCB does not add network latency to connection setup.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
“esnikeys” value of an SVCB response (). Clients
implementing this optimization SHOULD wait for 50 milliseconds before
starting optimistic pre-connection, as per the guidance in
.An SVCB record is consistent with a connection
if the client would attempt an equivalent connection when making use of
that record. If 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.
For example, suppose the client receives this SVCB RRSet for a protocol
that uses TLS over TCP:If the client has an in-progress TCP connection to [2001:db8::2]:1234,
it MAY proceed with TLS on that connection using esnikeys="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 .A nonconforming recursive resolver might not return all the information
required to use all the records in an SVCB response. 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.To avoid a delay for clients using a nonconforming recursive resolver,
domain owners SHOULD use a single SVCB record whose SvcDomainName is in the
origin hostname’s CNAME chain if possible. This will ensure that the required
address records are already present in the client’s DNS cache as part of the
responses to the address queries that were issued in parallel.A few initial SvcParamKeys are defined here. These keys are useful for
HTTPS, and most are applicable to other protocols as well.The “alpn” SvcParamKey defines the Application Layer Protocol
(ALPN, as defined in {{!RFC7301}) supported by a TLS-based alternative
service. Its value SHOULD be an entry in the IANA registry “TLS
Application-Layer Protocol Negotiation (ALPN) Protocol IDs”.The presentation format and wire format of SvcParamValue
is its registered “Identification Sequence”.Clients MUST ignore SVCB RRs where the “alpn” SvcParamValue
is unknown or unsupported.The “port” SvcParamKey defines the TCP or UDP port
that should be used to contact this alternative service.The presentation format of the SvcParamValue is a numeric value
between 0 and 65535 inclusive. The wire format of the SvcParamValue
is the corresponding 2 octet numeric value in network byte order.The SvcParamKey for ESNI is “esnikeys”. Its value is defined in
. It is applicable to most TLS-based protocols.When publishing a record containing an “esnikeys” parameter, the publisher
MUST ensure that all IP addresses of SvcDomainName correspond to servers
that have access to the corresponding private key or are authoritative
for the fallback domain. (See for more details about
the fallback domain.) This yields an anonymity set of cardinality equal
to the number of ESNI-enabled server domains supported by a given client-facing
server. Thus, even with SNI encryption, an attacker who can enumerate the
set of ESNI-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
ESNI-enabled server anonymity set. This probability may be increased via
traffic analysis or other mechanisms.The “ipv4hint” and “ipv6hint” keys represent IP address hints for the
service. If A and AAAA records for SvcDomainName are locally
available, the client SHOULD ignore these hints. Otherwise, clients
SHOULD perform A and/or AAAA queries for SvcDomainName as in
, 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 SvcDomainName. Failure to use A and/or
AAAA response addresses may negatively 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 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.These parameters MAY be repeated multiple times within a record.
When receiving such a record, clients SHOULD combine the sets of addresses.When selecting between IPv4 and IPv6 addresses to use, clients may use an
approach such as .
When only “ipv4hint” parameters are present, IPv6-only clients may synthesize
IPv6 addresses as specified in or ignore the “ipv4hint” key and
wait for AAAA resolution (). Recursive resolvers MUST NOT
perform DNS64 () on parameters within an SVCB record.
For best performance, server operators SHOULD include “ipv6hint” parameters
whenever they publish “ipv4hint” parameters.The presentation format for each parameter is a comma-separated list of
IP addresses in standard textual format .These parameters are intended to minimize additional connection latency
when a recursive resolver is not compliant with the requirements in
, and SHOULD NOT be included if most clients are using
compliant recursive resolvers.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 HTTPSSVC RR type is defined as an SVCB-compatible RR type,
specific to the https and http schemes.
This handling includes a mapping from HTTPSSVC records
directly into Alt-Svc entries. Clients MUST NOT
perform SVCB queries or accept SVCB responses for https
or http schemes.The HTTPSSVC wire format and presentation format are
identical to SVCB, and both share the SvcParamKey registry. SVCB
semantics apply equally to HTTPSSVC unless specified otherwise.The presence of an HTTPSSVC record for an HTTP or HTTPS service also
provides an indication that all resources are available over HTTPS, as
discussed in . This allows HTTPSSVC RRs to apply to
pre-existing HTTP scheme URLs, while ensuring that the client uses a
secure and authenticated HTTPS connection.The HTTPSSVC RR extends the concept
introduced in the HTTP Alternative Services proposed standard
. Alt-Svc defines:an extensible data model for describing alternative network endpoints
that are authoritative for an originthe “Alt-Svc Field Value”, a text format for representing this
informationstandards for sending information in this format from a server to a
client over HTTP/1.1 and HTTP/2.Each ServiceForm HTTPSSVC RR provides a set of information that can be
mapped into an Alt-Svc Field Value. A client receiving this
information during DNS resolution can skip the initial connection and
proceed directly to an alternative service.The HTTPSSVC RR extends the behavior for determining
a QNAME specified above in .
In particular, if the scheme is “https” with port 443, or the scheme
is “http” and the port is 80, then the client’s original QNAME is
equal to the origin host name.For origins other than https with port 443 and http with port 80,
the port and scheme continue to be prefixed to the hostname
as described in . Following of HTTPSSVC AliasForm and
CNAME aliases is also unchanged from SVCB.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 host.To construct an Alt-Svc Field Value (as defined in Section 4 of
) from an HTTPSSVC record:The SvcDomainName is mapped into the uri-host portion of alt-authority
with the trailing “.” removed.
(If SvcDomainName is “.”, the special handling described in
MUST be applied first.)The SvcParamValue of the “port” service parameter, or 443 if no such
parameter is present, is written to the port portion of the alt-authority.The SvcParamValue of the “alpn” service parameter is mapped to the
protocol-id. This MUST follow the normalization and encoding
requirements for protocol-id specified in Section 3.
This parameter is MANDATORY.The DNS TTL is mapped to the “ma” (max age) Alt-Svc parameter.For SVCB parameters with defined mappings to HTTPS Alt-Svc, each should be
included as an Alt-Svc parameter, typically as the SvcParamKey name
“=” a defined encoding of the SvcParamValue.Converting an Alt-Svc Field Value into an HTTPSSVC record follows the reverse
of this procedure.Conversion from HTTPSSVC to Alt-Svc Field Value SHOULD ignore any
unrecognized SvcParamKeys, and conversion from Alt-Svc Field Value to
HTTPSSVC SHOULD ignore any Alt-Svc parameters that do not have a
corresponding SvcParamKey.For example, if the operator of https://www.example.com
intends to include an HTTP response header likethey could also publish an HTTPSSVC DNS RRSet likeWhere “foo” is a hypothetical future HTTPSSVC and Alt-Svc parameter.This data type can also be represented as an Unknown RR as described in
:On connections to an HTTPSSVC alternative service, clients SHOULD
include the same Alt-Used header that they would include if the
corresponding Alt-Svc Field Value were received over HTTPS.Publishing an alternative services form HTTPSSVC record in DNS is intended
to be equivalent to transmitting the corresponding Alt-Svc value over
HTTPS, and receiving an HTTPSSVC record is intended to be equivalent to
receiving this field value over HTTPS. However, there are some small
differences in the intended client and server behavior.There is no SvcParamKey corresponding to the Alt-Svc “ma” (max age) parameter.
Instead, server operators SHOULD encode the
expiration time in the DNS TTL, and MUST NOT set a TTL longer than the
intended “max age”.For security reasons, there is no SvcParamKey corresponding to the Alt-Svc
“persist” parameter.Server operators MAY publish multiple ServiceForm HTTPSSVC
records as an RRSet. When converting a collection of alt-values
into an HTTPSSVC RRSet, the server operator MUST set the
overall TTL to a value no larger than the minimum
of the “max age” values (following Section 5.2 of ).Each RR corresponds to exactly one alt-value, as described
in Section 3 of .As discussed in , HTTPSSVC RRs with
a smaller SvcFieldPriority value SHOULD be sorted ahead of and given
preference over RRs with a larger SvcFieldPriority value.Clients SHOULD prefer Alt-values received via HTTPS over any Alt-value
received via DNS.The RRs SHOULD be ordered by increasing SvcFieldPriority, with shuffling
for equal SvcFieldPriority values. Clients MAY choose to further
prioritize alt-values where address records are immediately
available for the alt-value’s SvcDomainName.The client SHOULD concatenate the thus-transformed-and-ordered
SvcFieldValues in the RRSet, separated by commas. (This is
semantically equivalent to receiving multiple Alt-Svc HTTP response
headers, according to Section 3.2.2 of ).Sending Alt-Svc over HTTP allows the server to tailor the Alt-Svc
Field Value specifically to the client. When using an HTTPSSVC DNS
record, groups of clients will necessarily receive the same Alt-Svc
Field Value. Therefore, this standard is not suitable for uses that
require single-client granularity in Alt-Svc.Some DNS caching systems incorrectly extend the lifetime of DNS
records beyond the stated TTL. Server operators MUST NOT rely on
HTTPSSVC records expiring on time, and MAY shorten the TTL to compensate.By publishing an HTTPSSVC record, the server
operator indicates that all useful HTTP resources on that origin are
reachable over HTTPS, similar to HTTP Strict Transport Security
. When an HTTPSSVC record is present for an origin,
all “http” scheme requests for that origin SHOULD logically be redirected
to “https”.Prior to making an “http” scheme request, the client SHOULD perform a lookup
to determine if an HTTPSSVC record is available for that origin. To do so,
the client SHOULD construct a corresponding “https” URL as follows:Replace the “http” scheme with “https”.If the “http” URL explicitly specifies port 80, specify port 443.Do not alter any other aspect of the URL.This construction is equivalent to Section 8.3 of , point 5.If an HTTPSSVC record is present for this “https” URL, the client
should treat this as the equivalent of receiving an HTTP “307
Temporary Redirect” redirect to the “https” URL.
Because HTTPSSVC is 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.If the HTTPSSVC query results in a SERVFAIL error, and the connection
between the client and the recursive resolver is cryptographically protected
(e.g. using TLS or HTTPS ), the client SHOULD
abandon the connection attempt and display an error message. A SERVFAIL
error can occur if the domain is DNSSEC-signed, the recursive resolver is
DNSSEC-validating, and an active attacker between the recursive resolver
and the authoritative DNS server is attempting to prevent the upgrade to
HTTPS.Similarly, if the client enforces DNSSEC validation on A/AAAA responses,
it SHOULD abandon the connection attempt if the HTTPSSVC response fails
to validate.If the client has an Alt-Svc cache, and a usable Alt-Svc value is
present in that cache, then the client SHOULD NOT issue an HTTPSSVC DNS
query. Instead, the client SHOULD proceed with alternative service
connection as usual.If the client has a cached Alt-Svc entry that is expiring, the
client MAY perform an HTTPSSVC query to refresh the entry.Both SVCB/HTTPSSVC and Alt-Svc “esnikeys” parameters are defined for specifying
ESNI keys corresponding to an alternative service.
The value of the parameter is an ESNIKeys structure
or the empty string. ESNI-aware clients SHOULD prefer alt-values
and SVCB/HTTPSSVC RRs with non-empty esnikeys.Both the SVCB SvcParamValue presentation format as well
as the Alt-Svc parameter value is the ESNIKeys structure
encoded in or the empty string.
The SVCB SvcParamValue wire format is the octet string
containing the binary ESNIKeys structure.This parameter MAY also be sent in Alt-Svc HTTP response
headers and HTTP/2 ALTSVC frames. This parameter MUST NOT appear more than
once in a single alt-value.The Alt-Svc specification states that “the client MAY fall back to using
the origin” in case of connection failure (Section 2.4 of ).
This behavior is
not suitable for ESNI, because fallback would negate the privacy benefits of
ESNI.Accordingly, any connection attempt that uses ESNI MUST fall back only to
another alt-value that also has the esnikeys parameter. If the parameter’s
value is the empty string, the client SHOULD connect as it would in the
absence of any ESNIKeys information.For example, suppose a server operator has two alternatives. Alternative A
is reliably accessible but does not support ESNI. Alternative B supports
ESNI but is not reliably accessible. The server operator could include a
full esnikeys value in Alternative B, and mark Alternative A with esnikeys=””
to indicate that fallback from B to A is allowed.Other clients and services implementing SVCB or HTTPSSVC with esnikeys
are encouraged to take a similar approach.This standard is intended to reduce connection latency and
improve user privacy. Server operators implementing this standard
SHOULD also implement TLS 1.3 and OCSP Stapling
, 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
or DNS over HTTPS ).
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
. The scheme SHOULD have an
entry in the IANA URI Schemes Registry . The scheme
SHOULD have a defined specification for use with SVCB, unless it
already has a specification for use with Alt-Svc.SVCB/HTTPSSVC RRs and Alt-Svc Field Values are intended for distribution over untrusted
channels, and clients are REQUIRED to verify that the alternative
service is authoritative for the origin (Section 2.1 of ).
Therefore, DNSSEC signing and validation are OPTIONAL for publishing
and using SVCB and HTTPSSVC records.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 allows them to
track users or hinder their connections after they leave that network.The “Service Binding (SVCB) Parameter Registry” defines the name space
for parameters, including string representations and numeric
SvcParamKey values. This registry is shared with other SVCB-compatible
RR types, such as HTTPSSVC.ACTION: create and include a reference to this registry.A registration MUST include the following fields:Name: Service parameter key nameSvcParamKey: Service parameter key numeric identifier (range 0-65535)Meaning: a short descriptionPointer to specification textValues to be added to this name space require Expert Review (see
, Section 4.1). Apart from the initial contents, the name
MUST NOT start with “key”.The “Service Binding (SVCB) Parameter Registry” shall initially
be populated with the registrations below:SvcParamKeyNAMEMeaningReference0key0Reserved(This document)1alpnALPN for alternative service(This document)2portPort for alternative service(This document)3esnikeysESNI keys literal(This document)4ipv4hintIPv4 address hints(This document)5key5Reserved(This document)6ipv6hintIPv6 address hints(This document)65280-65534keyNNNNNPrivate Use(This document)65535key65535Reserved(This document)TODO: do we also want to reserve a range for greasing?Per , please add the following entry to the data type
range of the Resource Record (RR) TYPEs registry:TYPEMeaningReferenceSVCBService Location and Parameter Binding(This document)HTTPSSVCHTTPS Service Location and Parameter Binding(This document)Per , please add the following entries to the DNS Underscore
Global Scoped Entry Registry:RR TYPE_NODE NAMEMeaningReferenceHTTPSSVC_httpsAlt-Svc for HTTPS(This document)HTTPSSVC_httpAlt-Svc for HTTPS(This document)Per , please add the following entry to the HTTP Alt-Svc
Parameter Registry:Alt-Svc ParameterMeaningReferenceesnikeysEncrypted SNI keys(This document)There have been a wide range of proposed solutions over the years to
the “CNAME at the Zone Apex” challenge proposed. These include
,
, and others.Thank you to Ian Swett, Ralf Weber, Jon Reed,
Martin Thompson, Lucas Pardue, Ilari Liusvaara,
Tim Wicinski, Tommy Pauly, Chris Wood,
and others for their feedback and suggestions on this draft.Encrypted Server Name Indication for TLS 1.3This document defines a simple mechanism for encrypting the Server Name Indication for TLS 1.3.DNS Scoped Data Through "Underscore" Naming of Attribute LeavesFormally, any DNS resource record may occur under any domain name. However some services use an operational convention for defining specific interpretations of an RRset, by locating the records in a DNS branch, under the parent domain to which the RRset actually applies. The top of this subordinate branch is defined by a naming convention that uses a reserved node name, which begins with an _underscore. The underscored naming construct defines a semantic scope for DNS record types that are associated with the parent domain, above the underscored branch. This specification explores the nature of this DNS usage and defines the "DNS Global Underscore Scoped Entry Registry" with IANA. The purpose of the Underscore registry is to avoid collisions resulting from the use of the same underscore-based name, for different services.Hypertext Transfer Protocol Version 3 (HTTP/3)The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC, and describes how HTTP/2 extensions can be ported to HTTP/3.HTTP Alternative ServicesThis document specifies "Alternative Services" for HTTP, which allow an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol configuration.The Web Origin ConceptThis document defines the concept of an "origin", which is often used as the scope of authority or privilege by user agents. Typically, user agents isolate content retrieved from different origins to prevent malicious web site operators from interfering with the operation of benign web sites. In addition to outlining the principles that underlie the concept of origin, this document details how to determine the origin of a URI and how to serialize an origin into a string. It also defines an HTTP header field, named "Origin", that indicates which origins are associated with an HTTP request. [STANDARDS-TRACK]Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Domain names - implementation and specificationThis RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication.Augmented BNF for Syntax Specifications: ABNFInternet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]Happy Eyeballs Version 2: Better Connectivity Using ConcurrencyMany communication protocols operating over the modern Internet use hostnames. These often resolve to multiple IP addresses, each of which may have different performance and connectivity characteristics. Since specific addresses or address families (IPv4 or IPv6) may be blocked, broken, or sub-optimal on a network, clients that attempt multiple connections in parallel have a chance of establishing a connection more quickly. This document specifies requirements for algorithms that reduce this user-visible delay and provides an example algorithm, referred to as "Happy Eyeballs". This document obsoletes the original algorithm description in RFC 6555.Hypertext Transfer Protocol (HTTP/1.1): Semantics and ContentThe Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.SOCKS Protocol Version 5This memo describes a protocol that is an evolution of the previous version of the protocol, version 4 [1]. This new protocol stems from active discussions and prototype implementations. [STANDARDS-TRACK]Discovery of the IPv6 Prefix Used for IPv6 Address SynthesisThis document describes a method for detecting the presence of DNS64 and for learning the IPv6 prefix used for protocol translation on an access network. The method depends on the existence of a well-known IPv4-only fully qualified domain name "ipv4only.arpa.". The information learned enables nodes to perform local IPv6 address synthesis and to potentially avoid NAT64 on dual-stack and multi-interface deployments.DNS64: DNS Extensions for Network Address Translation from IPv6 Clients to IPv4 ServersDNS64 is a mechanism for synthesizing AAAA records from A records. DNS64 is used with an IPv6/IPv4 translator to enable client-server communication between an IPv6-only client and an IPv4-only server, without requiring any changes to either the IPv6 or the IPv4 node, for the class of applications that work through NATs. This document specifies DNS64, and provides suggestions on how it should be deployed in conjunction with IPv6/IPv4 translators. [STANDARDS-TRACK]A Recommendation for IPv6 Address Text RepresentationAs IPv6 deployment increases, there will be a dramatic increase in the need to use IPv6 addresses in text. While the IPv6 address architecture in Section 2.2 of RFC 4291 describes a flexible model for text representation of an IPv6 address, this flexibility has been causing problems for operators, system engineers, and users. This document defines a canonical textual representation format. It does not define a format for internal storage, such as within an application or database. It is expected that the canonical format will be followed by humans and systems when representing IPv6 addresses as text, but all implementations must accept and be able to handle any legitimate RFC 4291 format. [STANDARDS-TRACK]Handling of Unknown DNS Resource Record (RR) TypesExtending the Domain Name System (DNS) with new Resource Record (RR) types currently requires changes to name server software. This document specifies the changes necessary to allow future DNS implementations to handle new RR types transparently. [STANDARDS-TRACK]Clarifications to the DNS SpecificationThis document considers some areas that have been identified as problems with the specification of the Domain Name System, and proposes remedies for the defects identified. [STANDARDS-TRACK]HTTP Strict Transport Security (HSTS)This specification defines a mechanism enabling web sites to declare themselves accessible only via secure connections and/or for users to be able to direct their user agent(s) to interact with given sites only over secure connections. This overall policy is referred to as HTTP Strict Transport Security (HSTS). The policy is declared by web sites via the Strict-Transport-Security HTTP response header field and/or by other means, such as user agent configuration, for example. [STANDARDS-TRACK]Specification for DNS over Transport Layer Security (TLS)This document describes the use of Transport Layer Security (TLS) to provide privacy for DNS. Encryption provided by TLS eliminates opportunities for eavesdropping and on-path tampering with DNS queries in the network, such as discussed in RFC 7626. In addition, this document specifies two usage profiles for DNS over TLS and provides advice on performance considerations to minimize overhead from using TCP and TLS with DNS.This document focuses on securing stub-to-recursive traffic, as per the charter of the DPRIVE Working Group. It does not prevent future applications of the protocol to recursive-to-authoritative traffic.DNS Queries over HTTPS (DoH)This document defines a protocol for sending DNS queries and getting DNS responses over HTTPS. Each DNS query-response pair is mapped into an HTTP exchange.The Base16, Base32, and Base64 Data EncodingsThis document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]The Transport Layer Security (TLS) Protocol Version 1.3This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.Transport Layer Security (TLS) Extensions: Extension DefinitionsThis document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK]Guidelines and Registration Procedures for URI SchemesThis document updates the guidelines and recommendations, as well as the IANA registration processes, for the definition of Uniform Resource Identifier (URI) schemes. It obsoletes RFC 4395.Guidelines for Writing an IANA Considerations Section in RFCsMany protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.The "SNI" Alt-Svc ParameterHTTP Alternative Services provides a mechanism for an origin to declare that its content is accessible via some other combination of host, port, and protocol. In the process of using such an alternative, an observer can identify that the client is requesting resources from a particular hostname. This document extends HTTP Alternative Services, in combination with Secondary Certificate Authentication, to enable clients not to disclose the origin to which they intend to connect.DNS TerminologyThe Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document.This document obsoletes RFC 7719 and updates RFC 2308.Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and RoutingThe Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.Domain Name System (DNS) IANA ConsiderationsThis document specifies Internet Assigned Numbers Authority (IANA) parameter assignment considerations for the allocation of Domain Name System (DNS) resource record types, CLASSes, operation codes, error codes, DNS protocol message header bits, and AFSDB resource record subtypes. It obsoletes RFC 6195 and updates RFCs 1183, 2845, 2930, and 3597.A DNS Resource Record for HTTPThis document specifies an "HTTP" resource record type for the DNS to facilitate the lookup of the server hostname of HTTP(s) URIs. It is intended to replace the use of CNAME records for this purpose, and in the process provides a solution for the inability of the DNS to allow a CNAME to be placed at the apex of a domain name.Address-specific DNS aliases (ANAME)This document defines the "ANAME" DNS RR type, to provide similar functionality to CNAME, but only for type A and AAAA queries. Unlike CNAME, an ANAME can coexist with other record types. The ANAME RR allows zone owners to make an apex domain name into an alias in a standards compliant manner.A DNS RR for specifying the location of services (DNS SRV)This document describes a DNS RR which specifies the location of the server(s) for a specific protocol and domain. [STANDARDS-TRACK]The following:is equivalent to the Alt-Svc record:for the origins of both “https://www.example.com” and “https://example.com”.The SVCB and HTTPSSVC record 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.An SRV record 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:SRV records are typically mandatory, whereas clients will always
continue to function correctly without making use of Alt-Svc or SVCB.SRV records cannot instruct the client to switch or upgrade
protocols, whereas Alt-Svc can signal such an upgrade (e.g. to
HTTP/2).SRV records are not extensible, whereas SVCB and HTTPSSVC
can be extended with new parameters.Using SRV records would not allow an HTTPS client to skip processing of the
Alt-Svc information in a subsequent connection, so it does not confer
a performance advantage.Unlike , this approach is
extensible to cover Alt-Svc and ESNIKeys 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.Unlike , this approach is extensible to
cover Alt-Svc and ESNIKeys use-cases. This approach also does not
require any changes or special handling on either authoritative or
master 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.Unlike , this approach is extensible and covers
the Alt-Svc case as well as addresses the zone apex CNAME challenge.By using 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
different protocols and ports, rather than applying a single configuration
to all ports on a domain.Defining an Alt-Svc sni= parameter
(such as from ) would
have provided some benefits to clients and servers not implementing ESNI,
such as for specifying that “_wildcard.example.com” could be sent as an SNI
value rather than the full name. There is nothing precluding SVCB from
being used with an sni= parameter if one were to be defined, but it
is not included here to reduce scope, complexity, and additional potential
security and tracking risks.This draft is intended to be a work-in-progress for discussion.
Many details are expected to change with subsequent refinement.
Some known issues or topics for discussion are listed below.Naming is hard. “SVCB” and “HTTPSSVC” are proposed as placeholders
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, HTTPSSVC, SVCHTTPS, or something else.The SVCB record was designed as a generalization of HTTPSSVC,
based on feedback requesting a solution that applied to protocols
pther than HTTP. Past efforts
to over-generalize have not met with broad success, but we
hope that HTTPSSVC and SVCB have struck an acceptable balance between
generality and focus.Advice from experts in DNS wire format best practices would be greatly
appreciated to refine the proposed details, overall.The SvcFieldPriority could alternately be included as a pri= Alt-Svc attribute.
It wouldn’t be applicable for Alt-Svc returned via HTTP, but it is also
not necessarily needed by DNS servers. It is also not used for AliasForm RRs.Some other similar mechanisms such as SRV have a weight in-addition
to priority. That is excluded here for simplicity. It could always be
added as an optional SVCB parameter.draft-ietf-dnsop-svcb-httpssvc-00
Document an optimization for optimistic pre-connection. (Chris Wood)Relax IP hint handling requirements. (Eric Rescorla)draft-nygren-dnsop-svcb-httpssvc-00
Generalize to an SVCB record, with special-case
handling for Alt-Svc and HTTPS separated out
to dedicated sections.Split out a separate HTTPSSVC record for
the HTTPS use-case.Remove the explicit SvcRecordType=0/1 and instead
make the AliasForm vs ServiceForm be implicit.
This was based on feedback recommending against
subtyping RR type.Remove one optimization.draft-nygren-httpbis-httpssvc-03
Change redirect type for HSTS-style behavior
from 302 to 307 to reduce ambiguities.draft-nygren-httpbis-httpssvc-02
Remove the redundant length fields from the wire format.Define a SvcDomainName of “.” for SvcRecordType=1
as being the HTTPSSVC RRNAME.Replace “hq” with “h3”.draft-nygren-httpbis-httpssvc-01
Fixes of record name. Replace references to “HTTPSVC” with “HTTPSSVC”.draft-nygren-httpbis-httpssvc-00
Initial version