Internet DRAFT - draft-homburg-dnsop-codcp
draft-homburg-dnsop-codcp
DNSOP P.C. Homburg
Internet-Draft 7 July 2023
Intended status: Standards Track
Expires: 8 January 2024
Control Options For DNS Client Proxies
draft-homburg-dnsop-codcp-01
Abstract
The introduction of many new transport protocols for DNS in recent
years (DoT, DoH, DoQ) significantly increases the complexity of DNS
stub resolvers that want to support these protocols. A practical way
forward is to have a DNS client proxy in the host operating system.
This allows applications to communicate using Do53 and still get the
privacy benefit from using more secure protocols over the internet.
However, such a setup leaves the application with no control over
which transport the proxy uses. This document introduces EDNS(0)
options that allow a stub resolver to request certain transport and
allow the proxy to report capabilities and actual transports that are
available.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 January 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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Table of Contents
1. Discussion Venues . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Description . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. PROXY CONTROL OPTION . . . . . . . . . . . . . . . . . . . . 5
6.1. Security Constraints Sub-option . . . . . . . . . . . . . 6
6.2. Transport Priority Sub-option . . . . . . . . . . . . . . 8
6.3. SVC Parameter . . . . . . . . . . . . . . . . . . . . . . 9
6.4. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 10
6.5. Interface Name . . . . . . . . . . . . . . . . . . . . . 10
7. PROXY SCOPE OPTION . . . . . . . . . . . . . . . . . . . . . 11
8. TRUST ANCHOR OPTION . . . . . . . . . . . . . . . . . . . . . 12
9. Protocol Specification . . . . . . . . . . . . . . . . . . . 13
9.1. Client Processing . . . . . . . . . . . . . . . . . . . . 13
9.1.1. Probing . . . . . . . . . . . . . . . . . . . . . . . 13
9.1.2. Trust Anchor . . . . . . . . . . . . . . . . . . . . 14
9.2. Server Processing . . . . . . . . . . . . . . . . . . . . 14
10. Connection Between Stub Resolver And Proxy . . . . . . . . . 15
11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
14. Normative References . . . . . . . . . . . . . . . . . . . . 18
15. Informative References . . . . . . . . . . . . . . . . . . . 18
Appendix A. Change history . . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Discussion Venues
This note is to be removed before publishing as an RFC. Source for
this draft and an issue tracker can be found at
https://github.com/NLnetLabs/draft-homburg-dnsop-codc
(https://github.com/NLnetLabs/draft-homburg-dnsop-codc) .
2. Definitions
Do53 The original, plain text DNS transport as described in
[RFC1034][RFC1035]. Typically, UDP is used, with the DNS server
listening on port 53. Sometimes, for example, for large
responses, TCP is used, also on port 53.
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DoH DNS over HTTPS as described in [RFC8484].
DoT DNS over TLS as described in [RFC7858]
DoQ DNS over QUIC ([RFC9000]) as described in [I-D.ietf-dprive-
dnsoquic], not to be confused with DNS over HTTP/3 which also uses
QUIC
EDNS(0) Option An option as described in [RFC6891]
h2 This TLS ALPN identifies HTTP/2 as described in [RFC7540]
h3 This TLS ALPN identifies HTTP/3, which is HTTP over QUIC and is
described in I.D.ietf-quic-http (expired draft)
Interface Name A name that identifies a network interface as
described in [RFC3493]. In addition, an interface index converted
to a decimal number is also consider an interface name.
PKIX Public-Key Infrastructure using X.509. See [RFC5280]
3. Introduction
The introduction of many new transport protocols for DNS in recent
years (DoT, DoH, DoQ) significantly increases the complexity of DNS
stub resolvers that want to support these protocols. In addition,
for short-lived applications, the overhead of setting a DoH
connection is quite high if the application only needs to send a few
DNS requests.
A practical way forward is to have a DNS client proxy in the host
operating system. A local proxy may provide some benefit to short-
lived applications by caching results. In particular if the system
uses a so called 'public DNS resolver'. In general we assume that
the cache is tagged according to the source of a reply and the
transport it is received on.
This allows applications to communicate using Do53 and still get the
privacy benefits from using more secure protocols over the internet.
However, such a setup leaves the application with no control over
which transport the proxy uses. This document introduces EDNS(0)
options that allow a stub resolver to request certain transports and
allow the proxy to report capabilities and actual transports that are
available.
With respect to DNSSEC, we assume that an application that needs
DNSSEC validation, for example, for DANE validation or SSHFP, will
perform the DNSSEC validation within the application itself and does
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not trust the proxy. The proxy can of course do DNSSEC validation as
well. Important however, is that an untrusted proxy cannot provide
an application with a traditional (unsigned) trust anchor.
For the transport configuration we expect three levels of details.
The first is a choice between requiring authenticated encryption,
also allowing unauthenticated encryption or doing opportunistic
encryption on an best effort basis. The second level is where the
application also specifies the names and/or IP addresses of upstream
resolvers. The third level is where the application also specifies
which transports (Do53, DoT, DoH, DoQ) are allowed to be used. A
final transport parameter is the outgoing interface that is to be
used.
For authentication we can have a mix of PKIX and DANE. Options are
one of the two and not the other, both or one of the two.
In a response, the proxy reports the interface, resolver, and
transport used.
As described in Section 3 of [RFC5625], some simple DNS proxies may
just forward DNS packets without handling of EDNS(0) options. So
what could happen is that an application sends a privacy sensitive
request to local proxy, expecting the proxy upstream connection to be
encrypted. However, a simple proxy may just forward the request
unencrypted to another proxy, for example, one in a CPE that does
implement the protocol described in this document. So what could
happen is that the request travels unencrypted over a local lan, or
if proxies deeper in the network support this protocol, even further
without the application noticing that something is wrong.
To handle this case, we introduce an option where the proxy reports
whether the connection between the stub resolver and the proxy is
host-local, link-local, or site-local or global.
In the ideal case, the host operating system provides applications
with a secure way to access a DNSSEC trust anchor that is maintained
according to [RFC5011]. However in situations where this is not the
case, an application can fall back to [RFC7958]. However, for short
lived processes, there is considerable overhead in issuing two
HTTP(S) requests to data.iana.org to obtain the trust anchor XML file
and the signature over the trust anchor. For this reason, it makes
sense to let the proxy cache this information.
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4. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
5. Description
This document introduces three new EDNS(0) options, and one new
response code. This first option, called PROXY CONTROL Option,
specifies which transports a proxy should use to connect to a
recursive resolver.
The second option, called PROXY SCOPE Option, reports the IP address
scope of the connection between the application's stub resolver and
the proxy.
Finally, the TRUST ANCHOR Option, provides the application with a
DNSSEC trust anchor signed by IANA.
The BADPROXYPOLICY error is returned the proxy cannot meet the
requirements in a PROXY CONTROL Option or the option is malformed.
6. PROXY CONTROL OPTION
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: ~ Type-Length-Value (TLV) Sub-Options ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where
OPTION-CODE
To be decided (TBD1)
OPTION-LENGTH
Length of this option excluding the OPTION-CODE and OPTION-LENGTH
fields
The remainer is filled with a collection of TLV sub-options defined
next. All sub-options have the following format:
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+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: ~ Sub-Option Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where
SUB-OPTION-CODE
16-bit identifier for the sub-option
SUB-OPTION-LENGTH
Length of this sub-option excluding the SUB-OPTION-CODE and SUB-
OPTION-LENGTH fields
Sub-Option Data
Sub-option specific data
Associated with this option is a new error, BADPROXYPOLICY. When a
proxy cannot meet the requirements in a PROXY CONTROL Option or the
option is malformed, it returns this error.
If the proxy returns a BADPROXYPOLICY error, the proxy MAY include a
PROXY CONTROL Option that lists what the proxy can do. For example,
if authenticated encryption is not possible, but unauthenticated is,
then the proxy may include an option show that.
6.1. Security Constraints Sub-option
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | U |UA | A | P | D | Z |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
where
SUB-OPTION-CODE
To be decided
SUB-OPTION-LENGTH
2 (this sub-option defines a 16-bit flags field
U
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force the use of unencrypted communication (Do53)
UA
require encryption, authentication is allowed but not required
A
require authenticated encryption
P
authenticate using a PKIX certificate
D
authenticate using DANE
Z
reserved, MUST be zero when sending, MUST be ignored when received
This sub-option gives the security contraints of the DNS transports
that are used by the client proxy. The U, UA, and A flags are
mutually exclusive. If more than one flag is set, the proxy SHOULD
return a BADPROXYPOLICY error. There are four possibilities:
U = 0, UA = 0, A = 0 An effort is made to reach authenticated
encryption, if that fails, unauthenticated encryption is tried.
If that also fails, the proxy resorts to an unencrypted transport.
It is an error if either or both of the P or D flags is set and
the proxy SHOULD return a BADPROXYPOLICY error if that is the
case.
U = 1, UA = 0, A = 0 The proxy tries only unencrypted transports.
It is an error if either or both of the P or D flags is set and
the proxy SHOULD return a BADPROXYPOLICY error if that is the
case.
U = 0, UA = 1, A = 0 An effort is made to reach authenticated
encryption, if that fails, unauthenticated encryption is tried.
It is an error if either or both of the P or D flags is set and
the proxy SHOULD return a BADPROXYPOLICY error if that is the
case.
U = 0, UA = 0, A = 1 The proxy only tries authenticated encryption.
The P and D flags can be used to control which authentication
mechanism has to be used.
The P and D flags allow the application to require a specific
authentication mechanism (PKIX or DANE). The meaning of the flags is
the following:
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P = 0, D = 0 At least one of the two mechanisms has to validate for
authenticated encryption to succeed.
P = 1, D = 0 PKIX validation has to succeed, the status of DANE
validation is ignored.
P = 0, D = 1 A DANE record has to be present and be DNSSEC valid. A
DANE record has a Certificate Usage Field. For some values of
this field (the values zero and one), DANE requires PKIX
validation. In those cases, PKIX validation is also required
according to the DANE specifications. For the values two and
three, DANE does not require PKIX and because the P flag is zero,
the result of PKIX validation has to be ignored.
P = 1, D = 1 Both PKIX and DANE are required together. For PKIX,
this means that PKIX validation has to succeed. For DANE it means
that a DANE record has to be present and be DNSSEC valid.
Validation using the DANE record has to succeed.
Note that these two flags can only be used in combination with the A
flag. The proxy SHOULD return a BADPROXYPOLICY error if either or
both of the P or D flags is set and the A flag is clear.
6.2. Transport Priority Sub-option
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | TRANSPORT PROTOCOL | PRIORITY |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
where
SUB-OPTION-CODE
To be decided
SUB-OPTION-LENGTH
2
TRANSPORT PROTOCOL
A DNS transport protocol identifier. The value 0 is used to
specify any transport implemented by server.
PRIORITY
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The priority of this transport relative to other transports. The
value 0 indicates the highest priority and 254 the lowest. The
value 255 is defined to mean that this protocol MUST NOT be used.
Priorities are taken over all Proxy Control options in a DNS request.
This allows the application to specify an explicit order (or the lack
of order) among different upstream resolvers.
For protocol 0 (the default list), all protocols that are explicitly
listed in a Proxy Control option are excluded from the default list.
In other words, when processing the default list, all explicitly
listed protocols are excluded.
If this sub option is not present in a Proxy Control option, then the
proxy should assume protocol 0 at priority 128.
6.3. SVC Parameter
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | SVCPARAM KEY |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: ~ SVCPARAM ~
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
where
SUB-OPTION-CODE
To be decided
SUB-OPTION-LENGTH
Length of this sub-option excluding the SUB-OPTION-CODE and SUB-
OPTION-LENGTH fields
SVCPARAM KEY
Key of Svc parameters as defined in [ref]
SvcParam
Svc parameter value
This document take the meaning of SvcParamKeys 'alpn', 'port', and
'dohpath' from [draft-ietf-add-svcb-dns] with the exception that
'alpn' does not have to be present (i.e., the 'MUST be present'
requirement does not apply)
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Other relevant SvcParamKeys from [draft-ietf-dnsop-svcb-https] are
'mandatory', 'ech', 'ipv4hint' and 'ipv6hint'.
Instead of defining new sub-options to store IPv4 and IPv6 address,
this document re-uses the ipv4hints and ipv6hints. However the
semantics are redefined to be that these option and not hints, be are
the actual addresses that are to be used.
6.4. Domain Name
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: ~ DOMAIN NAME ~
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
where
SUB-OPTION-CODE
To be decided
SUB-OPTION-LENGTH
Length of this sub-option excluding the SUB-OPTION-CODE and SUB-
OPTION-LENGTH fields
DOMAIN NAME
domain name for authentication or resolving IP addresses. The
domain name is encoded in uncompressed DNS wire format.
If the option contains a domain name but no IP addresses (ipv4hints
or ipv6hints) then the proxy is expected to resolve the name to
addresses. If only addresses are specified then the proxy assumes
that no name is known (though a PKIX certificate may include an
address literal in the subjectAltName). If both a name and addresses
are specified then the proxy will use the specified addresses to
reach the upstream resolver and use the name for authentication.
The the option contains neither a domain name nor any IP addresses
then the application requests the resolvers known to the proxy.
6.5. Interface Name
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+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | SUB-OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SUB-OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: ~ INTERFACE NAME ~
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
where
SUB-OPTION-CODE
To be decided
SUB-OPTION-LENGTH
Length of this sub-option excluding the SUB-OPTION-CODE and SUB-
OPTION-LENGTH fields
INTERFACE NAME
name of outgoing interface for transport connections
An application may want to specify a DNS resolver that is reachable
through an IPv6 link-local address. IPv6 link-local addresses are
special in that they require a zone to be specified, either
explicitly or implicitly. Typically for a link-local address that
appears as a source or destination address, the zone is implicitly
the zone of the link the packet travels on. For packets that travel
between hosts, there is no goed way to explictly specify the zone of
a link-local address because two different hosts do not agree on zone
names. However, if the proxy is on the same host as the application,
then the zone identifier for the link-local address can be specified
in the Interface field. For this purpose an interface name can also
be an interface index expressed as a decimal string.
7. PROXY SCOPE OPTION
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | Scope |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
OPTION-CODE
To be decided (TBD2)
OPTION-LENGTH
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Length of this option excluding the OPTION-CODE and OPTION-LENGTH
fields
Scope
Scope of the source address of a request. Scope can have the
following values:
+=======+============+
| Value | Scope |
+=======+============+
| 0 | Undefined |
+-------+------------+
| 1 | Host local |
+-------+------------+
| 2 | Link local |
+-------+------------+
| 3 | Site local |
+-------+------------+
| 4 | Global |
+-------+------------+
Table 1
The purpose of this option is to deal with proxies that forward DNS
traffic without first removing any EDNS(0) options. The option
requests the DNS proxy that processes the option to report the scope
of the source address.
8. TRUST ANCHOR OPTION
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | ANCHORS-XML-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: ~ ANCHORS-XML ~
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | ANCHORS-P7S-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: ~ ANCHORS-P7S ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where
OPTION-CODE
To be decided (TBD3)
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OPTION-LENGTH
Length of this option excluding the OPTION-CODE and OPTION-LENGTH
fields
ANCHORS-XML-LENGTH
Length of ANCHORS-XML in network byte order
ANCHORS-XML
Trust anchors in XML format
ANCHORS-P7S-LENGTH
Length of ANCHORS-P7S in network byte order
ANCHORS-P7S
Signature in p7s format
This option provides DNSSEC trust anchors as described in [RFC7958].
9. Protocol Specification
9.1. Client Processing
A stub resolver that wishes to use the PROXY CONTROL Option includes
the option in all outgoing DNS requests that require privacy. The
option should be initialized according to the needs of the
application. In addition the PROXY SCOPE Option can be added. In
requests, the Scope field is set to undefined.
If the stub resolver receives a reply without a PROXY CONTROL Option
included in the reply, then stub resolver has to assume that traffic
will have Do53 levels of privacy. Similarly, a lack of a PROXY SCOPE
Option implies a global scope.
If the stub resolver receives a BADPROXYPOLICY error then the proxy
was unable to meet the requirements of the PROXY CONTROL Option.
9.1.1. Probing
In cases where the stub resolver expects a local DNS proxy, or where
the stub resolver has (a limited) fall back to more private
transports, or when the security policy of the application is such
that is better to fail than send queries over Do53, the stub resolver
first sends a probing query to verify that the proxy supports the
PROXY CONTROL and PROXY SCOPE Options.
This request queries "resolver.arpa" for SOA records. The proxy MUST
implement this as a Special Use Domain Name. The actual response is
not important. The important part is that the proxy returns PROXY
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CONTROL and PROXY SCOPE Options as described in this document or sets
the response code to BADPROXYPOLICY if it cannot meet specified
policy.
9.1.2. Trust Anchor
In the ideal case, the host operating system provides applications
with a secure way to access a DNSSEC trust anchor that is maintained
according to [RFC5011]. However in situations where this is not the
case, an application can fall back to [RFC7958]. However, for short
lived processes, there is considerable overhead in issuing two
HTTP(S) requests to data.iana.org to obtain the trust anchor XML file
and the signature over the trust anchor. For this reason, it makes
sense to let the proxy cache this information.
If the local operating system does not provide a DNSSEC trust anchor,
then the application can ask the proxy. The stub resolver adds the
TRUST ANCHOR Option with ANCHORS-XML-LENGTH and ANCHORS-P7S-LENGTH
set to zero. If the proxy returns both an ANCHORS-XML and an
ANCHORS-P7S, then the application verifies the trust anchor using the
trust anchor certificate (which needs to come with the application).
9.2. Server Processing
Proxies are encouraged to cache options that appear in requests under
the assumption that a stub resolver will send multiple requests. If
a proxy caches DNS responses then the proxy MUST tag cached responses
with the properties of the DNS transport. When responding to later
requests, the proxy returns a cached entry only if the parameters of
the DNS transport match what is specified in the request.
When a proxy receives a new set of requirements, the proxy compiles a
list of addresses to connect to and a list of transports to try per
address. The proxy SHOULD prefer more private transports over less
private ones.
If the proxy cannot obtain a connection to a recursive resolver in a
way that matches the provided policy, then the proxy sets the
BADPROXYPOLICY response code in the reply.
The proxy MUST implement "resolver.arpa" as a locally served zone.
Proxies SHOULD respond to all queries with NODATA unless other
behavior is specified in a different document.
If the proxy successfully connects to a recursive resolver and
receives a reply, or the query is for a special use domain name that
is handled internally in the proxy, then the proxy add a PROXY
CONTROL Options dat details the connection to the recursive resolver
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(i.e., the U, UA, or A flag depending on encryption and
authentication, P and or D for authenticated connections, A53, AT,
AH2, AH3, or AQ depending on the transport (or none of those for a
future transport). Furthermore the proxy includes the address it
connected to, the Domain Name if known, any Service Parameters and
the outgoing interface name if known.
If the proxy finds a PROXY SCOPE Option, then it calculates the scope
from the source address. The proxy adds a PROXY SCOPE Option to a
reply and sets the value of Scope to the actual scope of the source
address of the request.
If the request contains a TRUST ANCHOR Option, then the proxy tries
to fetch the trust anchor XML and p7s files if it does not have them
already. If fetching one or both fails then the proxy sets the
corresponding length to zero. It is not clear how long the proxy can
cache this information. [RFC7958] Does not describe how long these
documents can be cache. A simple solution is to take the Expires
header in the HTTP reply. The proxy adds a TRUST ANCHOR Option to
the reply.
10. Connection Between Stub Resolver And Proxy
Absent other configuration, a stub resolver that implements this
standard SHOULD connect to the proxy using Do53 and as remote address
either ::1 or 127.0.0.1. In particular, the stub resolver SHOULD
avoid using name servers listed in files such as /etc/resolv.conf.
The reason for this is to simplify the integration of local DNS
proxies in existing environments. If the stub resolver ignores /etc/
resolv.conf then the proxy can use that information to connect to
recursive resolvers.
If no DNS server is responding to queries sent using Do53 to ::1 and
127.0.0.1, or if the response indicates that this standard is not
supported, then the stub resolver MAY fall back to traditional
configuration methods, such as /etc/resolv.conf. However, in that
case the stub resolver MUST make sure that doing so does not violate
the policy set by the application.
11. Security Considerations
A privacy sensitive application SHOULD first issue a SOA query for
resolver.arpa to verify that the local proxy supports the options
documented in the document. If the proxy does not support this
document then the application can refrain from sending queries that
reveal privacy sensitive names.
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By setting the interface name, an application can select an outging
interface on the proxy. Proxies should make sure that a query
receives from a process that is authorized to do so. By default, a
proxy SHOULD allow only process on the same host to use this feature.
If an unauthorized process includes an option with the interface name
set, then the proxy SHOULD return the BADPROXYPOLICY error.
12. IANA Considerations
IANA has assigned the following DNS EDNS0 option codes:
Value Name Status Reference
------- -------------- ---------- -----------
TBD1 PROXY CONTROL Standard RFC xxxx
TBD2 PROXY SCOPE Standard RFC xxxx
TBD3 TRUST ANCHOR Standard RFC xxxx
IANA has assigned the following Extended DNS Error code:
INFO-CODE Name Purpose Reference
----------- ---------------- ----------------------------- -----------
28 BADPROXYPOLICY Unable to conform to policy RFC xxxx
This document requests IANA to create a new registry for Proxy
Control Sub Options in the group Domain Name System (DNS) Parameters.
Expert review shall be required to add new entries to the registry.
The initial contents of the Proxy Control Sub Options registry shall
be:
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+=========+============+======================+===========+
| Value | Name | Description | Reference |
+=========+============+======================+===========+
| 0 | | Reserved | |
+---------+------------+----------------------+-----------+
| 1 | SECCON | Security Constraints | RFC xxxx |
+---------+------------+----------------------+-----------+
| 2 | TRANSPRIO | Transport Priority | RFC xxxx |
+---------+------------+----------------------+-----------+
| 3 | SVCPARAM | SVC Parameter | RFC xxxx |
+---------+------------+----------------------+-----------+
| 4 | DOMAINNAME | Domain Name | RFC xxxx |
+---------+------------+----------------------+-----------+
| 5 | INFNAME | Interface Name | RFC xxxx |
+---------+------------+----------------------+-----------+
| 6-65535 | | Unassigned | |
+---------+------------+----------------------+-----------+
Table 2
This document also requests IANA to create a new registry for DNS
Transport Protocols in the group Domain Name System (DNS) Parameters.
An RFC shall be required to add new entries to the registry.
+=======+==========+==================================+===========+
| Value | Name | Description | Reference |
+=======+==========+==================================+===========+
| 0 | DEFAULT | default protocols | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 1 | Do53 | Unencrypted UDP, fallback to TCP | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 2 | Do53-UDP | Unencrypted UDP, no fallback to | RFC xxxx |
| | | TCP | |
+-------+----------+----------------------------------+-----------+
| 3 | Do53-TCP | Unencrypted TCP | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 4 | DoT | DNS over TLS | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 5 | DoH | DNS over HTTPS | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 6 | DoQ | DNS over QUIC | RFC xxxx |
+-------+----------+----------------------------------+-----------+
| 7-255 | | Unassigned | |
+-------+----------+----------------------------------+-----------+
Table 3
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13. Acknowledgements
Many thanks to Yorgos Thessalonikefs and Willem Toorop for their
feedback.
14. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
15. Informative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, DOI 10.17487/RFC3493, February 2003,
<https://www.rfc-editor.org/info/rfc3493>.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <https://www.rfc-editor.org/info/rfc5011>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
<https://www.rfc-editor.org/info/rfc5625>.
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[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC7958] Abley, J., Schlyter, J., Bailey, G., and P. Hoffman,
"DNSSEC Trust Anchor Publication for the Root Zone",
RFC 7958, DOI 10.17487/RFC7958, August 2016,
<https://www.rfc-editor.org/info/rfc7958>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
Appendix A. Change history
(This section to be removed by the RFC editor.)
* draft-homburg-dnsop-codcp-01
- Moved draft to a separate git repository
(https://github.com/NLnetLabs/draft-homburg-dnsop-codc
(https://github.com/NLnetLabs/draft-homburg-dnsop-codc))
* draft-homburg-dnsop-codcp-00
- Renamed to draft-homburg-dnsop-codcp
- IANA section with allocated code point for BADPROXYPOLICY
- Proxy Control Option rewritten to be TLV-based
- Two new registries for sub-options and for DNS transports
* draft-homburg-add-codcp-00
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- Initial version
Author's Address
Philip Homburg
Email: philip@nlnetlabs.nl
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