Service binding and parameter specification via the DNS (DNS SVCB and HTTPS RRs)Googlebemasc@google.comAkamai Technologiesmbishop@evequefou.beAkamai Technologieserik+ietf@nygren.org
General
DNSOP Working GroupInternet-DraftThis 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.
The most recent working version of the document, open issues, etc. should all be
available there. The authors (gratefully) accept pull requests.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 ).
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 (). The HTTPS RR is then defined as a special
case of SVCB that improves efficiency and convenience for use with HTTPS
() by avoiding the need for an Attrleaf label
(). 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.
describes additional behaviors
specific to the HTTPS RR. 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, 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 as one example.The goal of the SVCB RR is to allow clients to resolve a single
additional DNS RR in a way that:Provides alternative endpoints that are authoritative for the service,
along with parameters associated with each of these endpoints.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.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:Connect directly to HTTP3 (QUIC transport)
alternative endpoints Obtain the Encrypted ClientHello keys associated with an
alternative endpointSupport non-default TCP and UDP portsEnable SRV-like benefits (e.g. apex delegation, as mentioned above) for HTTP(S),
where SRV has not been widely adoptedProvide an HSTS-like indication signaling that the HTTPS
scheme should be used instead of HTTP for this request (see ).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:SvcPriority: The priority of this record (relative to others,
with lower values preferred). A value of 0 indicates AliasMode.
(Described in .)TargetName: The domain name of either the alias target (for
AliasMode) or the alternative endpoint (for ServiceMode).SvcParams (optional): A list of key=value pairs
describing the alternative endpoint at
TargetName (only used in ServiceMode and otherwise ignored).
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 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
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 ClientHello
keys. See .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.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” .The “service name” is the host portion of the authority.The “authority endpoint” is the authority’s hostname and a port number implied
by the scheme or specified in the URI.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 .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 when, and only when, they
appear in all capitals, as shown here.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 .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 .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 .The presentation format of the record is:The SVCB record is defined specifically within
the Internet (“IN”) Class ().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 ().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 ,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 (), 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 (),
splitting on unescaped commas to produce a list of zero or more values.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.The RDATA for the SVCB RR consists of:a 2 octet field for SvcPriority as an integer in network
byte order.the uncompressed, fully-qualified TargetName, represented as
a sequence of length-prefixed labels as in Section 3.1 of .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:a 2 octet field containing the SvcParamKey as an
integer in network byte order. (See for the defined values.)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 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:the parser reaches the end of the RDATA while parsing the SvcParams.SvcParamKeys are not in strictly increasing numeric order.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.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 ), 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 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: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: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://”.(Parentheses are used to ignore a line break ( Section 5.1).)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.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: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: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.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.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.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.If TargetName has the value “.” (represented in the wire format as a
zero-length label), special rules apply.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.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:A SVCB-aware client selects an endpoint for a service using the following
procedure:Let $ADDR_QNAME be the service name. Let $SVCB_QNAME be the service name
plus appropriate prefixes for the scheme (see ).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.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
).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.Try to use the endpoint consisting of $ADDR_QNAME, the authority endpoint’s
port number, and no SvcParams.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 .Some important optimizations are discussed in
to avoid additional latency in comparison to ordinary AAAA/A lookups.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 or HTTPS
), 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.Clients using a domain-oriented transport proxy like HTTP CONNECT
( Section 4.3.6) or SOCKS5 () 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 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: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).It allows the service 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 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.Recursive resolvers that are aware of SVCB SHOULD help the client to
execute the procedure in 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
). 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.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:Incorporate the results of SVCB resolution. If the chain length limit has
been reached, terminate successfully (i.e. a NOERROR response).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.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 ).See for possible optimizations of this procedure.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 (),
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).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 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
“echconfig” value of a 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 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: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 .When following the procedure in , 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 ( 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 , clients MUST be able to fetch additional
information that is required to use a SVCB record, if it is not 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.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 ). For foo://foo.example.com:8080,
this might look like:Domain owners SHOULD avoid using a SvcDomainName that is below a DNAME, as
this is likely unnecessary and makes responses slower and larger.A few initial SvcParamKeys are defined here. These keys are useful for
HTTPS, and most are applicable to other protocols as well.The “alpn” and “no-default-alpn” SvcParamKeys together
indicate the set of Application Layer Protocol Negotation (ALPN)
protocol identifiers
and associated transport protocols supported by this service endpoint.As with Alt-Svc , 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” 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-ids 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 MUSTLet SVCB-ALPN-Intersection be the set of protocols in the SVCB ALPN set
that the client supports.Let Intersection-Transports be the set of transports (e.g. TLS, DTLS, QUIC)
implied by the protocols in SVCB-ALPN-Intersection.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”].Once the client has constructed a ClientHello, protocol negotiation in that
handshake proceeds as specified in , 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.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.The SvcParamKey to enable Encrypted ClientHello (ECH) is “echconfig”. Its
value is defined in . 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 to servers
that have access to the corresponding private key or are authoritative
for the public name. (See Section 7.2.2 of 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.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
, 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 . 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 .
When only “ipv4hint” is 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 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
, 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 “.”), server operators
SHOULD NOT include these hints, because they are unlikely to convey any
performance benefit.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
(). 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: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.)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 equally to HTTPS RRs unless specified otherwise.
The presentation format of the record is:As with SVCB, the record is defined specifically within
the Internet (“IN”) Class .All the SvcParamKeys defined in are permitted for use in
HTTPS RRs. The default set of ALPN IDs is the single value “http/1.1”.
The “automatically mandatory” keys () 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 . 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
. Clients and servers that implement HTTPS RRs are
not required to implement Alt-Svc.The HTTPS RR uses Port Prefix Naming (),
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
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 , 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.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.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 are ambiguous, and
problematic in some interpretations. We should update
to give it well-defined semantics that match HTTPS RRs.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.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.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.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 ().For clients that implement support for ECH, the interaction between
HTTPS RRs and Alt-Svc is described in .This specification does not alter the DNS queries performed when connecting
to an Alt-Svc hostname (typically A and/or AAAA only).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.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 .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: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 HTTPS RR query for this “https” URL returns any AliasMode HTTPS RRs,
or any compatible ServiceMode HTTPS RRs (see ), 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 .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
opening handshake from the W3C Fetch specification 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.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
, including the redundant length prefix. In presentation format,
the value is a single ECHConfigs encoded in 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 . 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 apply only to the inner
ClientHello. Similarly, it is the inner ClientHello whose Server Name Indication
identifies the desired service.The general client behavior specified in 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:Perform connection establishment using HTTPS RRs as described in
, 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.If the client implements Alt-Svc, try to connect using any entries from
the Alt-Svc cache.Fall back to address records (steps 5 and 6 of ) if
necessary.As a latency optimization, clients MAY prefetch DNS records for later steps
before they are needed.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.Consider a simple zone of the form:The domain owner could add this record: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).Consider a zone that is using CNAME aliasing:With HTTPS RRs, the owner of aliased.example could alias the apex by
adding one additional record: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.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: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, 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.For services other than HTTPS, the SVCB RR and an Attrleaf label
will be used. For example, to reach an example resource of
“baz://api.example.com:8765”, the following 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:HTTPS RRs use similar Attrleaf labels if the origin contains
a non-default port.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.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 ).
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 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 (), and disable the encryption enabled by the echconfig
SvcParamKey (). To prevent downgrades,
recommends that clients abandon the connection attempt when such an attack is
detected.A hostile DNS intermediary might forge AliasForm “.” records () 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.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: SVCBValue: 64Meaning: General Purpose Service EndpointsReference: This documentThis 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: HTTPSValue: 65Meaning: HTTPS Specific Service EndpointsReference: This documentThe “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.A registration MUST include the following fields:Number: SvcParamKey wire format numeric identifier (range 0-65535)Name: SvcParamKey presentation nameMeaning: a short descriptionPointer to specification textSvcParamKey entries to be added to this namespace
have different policies (, Section 4.1)
based on their range:NumberIANA Policy0-255Standards Action256-32767Expert Review32768-65280First Come First Served65280-65534Private Use65535Standards ActionApart from the initial contents, the SvcParamKey
name MUST NOT start with “key”.The “Service Binding (SVCB) Parameter Registry” shall initially
be populated with the registrations below:NumberNameMeaningReference0mandatoryMandatory keys in this RR(This document)1alpnAdditional supported protocols(This document)2no-default-alpnNo support for default protocol(This document)3portPort for alternative endpoint(This document)4ipv4hintIPv4 address hints(This document)5echconfigEncrypted ClientHello info(This document)6ipv6hintIPv6 address hints(This document)65280-65534keyNNNNNPrivate Use(This document)65535key65535Reserved (“Invalid key”)(This document)TODO: do we also want to reserve a range for greasing?Per , please add the following entries to the data type
range of the Resource Record (RR) TYPEs registry:TYPEMeaningReferenceSVCBService Location and Parameter Binding(This document)HTTPSHTTPS Service Location and Parameter Binding(This document)Per , please add the following entry to the DNS Underscore
Global Scoped Entry Registry:RR TYPE_NODE NAMEMeaningReferenceHTTPS_httpsHTTPS SVCB info(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 Thomson, Lucas Pardue, Ilari Liusvaara,
Tim Wicinski, Tommy Pauly, Chris Wood, David Benjamin,
and others for their feedback and suggestions on this draft.TLS Encrypted Client HelloThis document describes a mechanism in Transport Layer Security (TLS) for encrypting a ClientHello message under a server public key.Scoped Interpretation of DNS Resource Records through "Underscored" Naming of Attribute LeavesFormally, any DNS Resource Record (RR) 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 the underscore character (e.g., "_name"). 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 "Underscored and Globally Scoped DNS Node Names" registry with IANA. The purpose of this registry is to avoid collisions resulting from the use of the same underscored 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 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]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.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.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]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]DNAME Redirection in the DNSThe DNAME record provides redirection for a subtree of the domain name tree in the DNS. That is, all names that end with a particular suffix are redirected to another part of the DNS. This document obsoletes the original specification in RFC 2672 as well as updates the document on representing IPv6 addresses in DNS (RFC 3363). [STANDARDS-TRACK]Indicating Resolver Support of DNSSECIn order to deploy DNSSEC (Domain Name System Security Extensions) operationally, DNSSEC aware servers should only perform automatic inclusion of DNSSEC RRs when there is an explicit indication that the resolver can understand those RRs. This document proposes the use of a bit in the EDNS0 header to provide that explicit indication and describes the necessary protocol changes to implement that notification. [STANDARDS-TRACK]Transport Layer Security (TLS) Application-Layer Protocol Negotiation ExtensionThis document describes a Transport Layer Security (TLS) extension for application-layer protocol negotiation within the TLS handshake. For instances in which multiple application protocols are supported on the same TCP or UDP port, this extension allows the application layer to negotiate which protocol will be used within the TLS connection.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]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]The WebSocket ProtocolThe WebSocket Protocol enables two-way communication between a client running untrusted code in a controlled environment to a remote host that has opted-in to communications from that code. The security model used for this is the origin-based security model commonly used by web browsers. The protocol consists of an opening handshake followed by basic message framing, layered over TCP. The goal of this technology is to provide a mechanism for browser-based applications that need two-way communication with servers that does not rely on opening multiple HTTP connections (e.g., using XMLHttpRequest or <iframe>s and long polling). [STANDARDS-TRACK]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.Fetch Living StandardParameterized Nameserver Delegation with NS2 and NS2TWithin the DNS, there is no mechanism for authoritative servers to advertise which transport methods they are capable of. If secure transport methods are adopted by authoritative operators, protocol negotiation would be required. This document provides two new Resource Record Types, NS2 and NS2T, to facilitate that negotiation by allowing zone owners to signal how the authoritative nameserver(s) for their zone(s) may accept queries.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]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]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.Uniform Resource Identifier (URI): Generic SyntaxA Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]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 address 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.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 .
Here we summarize the allowed input to that algorithm, using ABNF: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.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”.For example, consider these char-string SvcParamValues:Character-string decoding either of these inputs would produce a single *OCTET
output:Value-list decoding either of these inputs would instead convert it to a list of
two list-values: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.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 SVCB.SRV records cannot instruct the client to switch or upgrade
protocols, whereas SVCB can signal such an upgrade (e.g. to
HTTP/2).SRV records are not extensible, whereas SVCB and HTTPS RRs
can be extended with new parameters.SVCB records use 16 bit for SvcPriority for consistency
with SRV and other RR types that also use 16 bit priorities.Unlike , 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.Unlike , 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.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.draft-ietf-dnsop-svcb-https-01
Added a “mandatory” SvcParamKeyAdded the ability to indicate that a service does not existAdjusted resolution and ALPN algorithmsMajor terminology revisions for “origin” and CamelCase namesRevised ABNFInclude allocated RR type numbersVarious corrections, explanations, and recommendationsdraft-ietf-dnsop-svcb-https-00
Rename HTTPSSVC RR to HTTPS RRRename “an SVCB” to “a SVCB”Removed “design considerations and open issues” section and some other “to be removed” textdraft-ietf-dnsop-svcb-httpssvc-03
Revised chain length limit requirementsRevised IANA registry rules for SvcParamKeysRequire HTTPS clients to implement SNIUpdate terminology for Encrypted ClientHelloClarifications: non-default ports, transport proxies, HSTS procedure, WebSocket behavior, wire format, IP hints, inner/outer ClientHello with ECHVarious textual and ABNF correctionsdraft-ietf-dnsop-svcb-httpssvc-02
All changes to Alt-Svc have been removedExpanded and reorganized examplesPriority zero is now the definition of AliasFormRepeated SvcParamKeys are no longer allowedThe “=” sign may be omitted in a key=value pair if the value is also emptyIn the wire format, SvcParamKeys must be in sorted orderNew text regarding how to handle resolution timeoutsExpanded description of recursive resolver behaviorMuch more precise description of the intended ALPN behaviorMatch the HSTS specification’s language on HTTPS enforcementRemoved ‘esniconfig=””’ mechanism and simplified ESNI connection logicdraft-ietf-dnsop-svcb-httpssvc-01
Reduce the emphasis on conversion between HTTPSSVC and Alt-SvcMake the “untrusted channel” concept more precise.Make SvcFieldPriority = 0 the definition of AliasForm, instead of a requirement.draft-ietf-dnsop-svcb-httpssvc-00
Document an optimization for optimistic pre-connection. (Chris Wood)Relax IP hint handling requirements. (Eric Rescorla)draft-nygren-dnsop-svcb-httpssvc-00
Generalize to an SVCB record, with special-case
handling for Alt-Svc and HTTPS separated out
to dedicated sections.Split out a separate HTTPSSVC record for
the HTTPS use-case.Remove the explicit SvcRecordType=0/1 and instead
make the AliasForm vs ServiceForm be implicit.
This was based on feedback recommending against
subtyping RR type.Remove one optimization.draft-nygren-httpbis-httpssvc-03
Change redirect type for HSTS-style behavior
from 302 to 307 to reduce ambiguities.draft-nygren-httpbis-httpssvc-02
Remove the redundant length fields from the wire format.Define a SvcDomainName of “.” for SvcRecordType=1
as being the HTTPSSVC RRNAME.Replace “hq” with “h3”.draft-nygren-httpbis-httpssvc-01
Fixes of record name. Replace references to “HTTPSVC” with “HTTPSSVC”.draft-nygren-httpbis-httpssvc-00
Initial version