ADD M. Boucadair
Internet-Draft Orange
Intended status: Standards Track T. Reddy
Expires: August 23, 2021 McAfee
D. Wing
Citrix
V. Smyslov
ELVIS-PLUS
February 19, 2021
Internet Key Exchange Protocol Version 2 (IKEv2) Configuration for
Encrypted DNS
draft-btw-add-ipsecme-ike-02
Abstract
This document specifies a new Internet Key Exchange Protocol Version
2 (IKEv2) Configuration Payload Attribute Types for encrypted DNS
with a focus on DNS-over-HTTPS (DoH), DNS-over-TLS (DoT), and DNS-
over-QUIC (DoQ).
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 23, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Sample Deployment Scenarios . . . . . . . . . . . . . . . . . 4
3.1. Roaming Enterprise Users . . . . . . . . . . . . . . . . 4
3.2. VPN Service Provider . . . . . . . . . . . . . . . . . . 4
3.3. DNS Offload . . . . . . . . . . . . . . . . . . . . . . . 5
4. IKEv2 Configuration Payload Attribute Types for Encrypted DNS 5
4.1. ENCDNS_IP*_* Configuration Payload Attributes . . . . . . 5
4.2. ENCDNS_URI_TEMPLATE Configuration Payload Attribute . . . 6
5. IKEv2 Protocol Exchange . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. Configuration Payload Attribute Types . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document specifies encrypted DNS configuration for an Internet
Key Exchange Protocol Version 2 (IKEv2) [RFC7296] initiator,
particularly the Authentication Domain Name (ADN) of DNS-over-HTTPS
(DoH) [RFC8484], DNS-over-TLS (DoT) [RFC7858], or DNS-over-QUIC (DoQ)
[I-D.ietf-dprive-dnsoquic].
This document introduces new IKEv2 Configuration Payload Attribute
Types (Section 4) for the support of DoT, DoH, and DoQ DNS servers.
These attributes can be used to provision authentication domain
names, a list of IP addresses, alternate port numbers, and a list of
DoH URI Template. The use of IKEv2 to provide these template is
meant to allow deployments where customized DoH configuration (e.g.,
per-subscriber or per-site) is required.
Sample use cases are discussed in Section 3. The Configuration
Payload Attribute Types defined in this document are not specific to
these deployments, but can also be used in other deployment contexts.
It is out of the scope of this document to provide a comprehensive
list of deployment contexts.
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The encrypted DNS server hosted by the VPN provider can get a domain-
validate certificate from a public CA. The VPN client does not need
to be provisioned with the root certificate of a private CA to
authenticate the certificate of the encrypted DNS server. The
encrypted DNS server can run on private IP addresses and its access
can be restricted to clients connected to the VPN.
Note that, for many years, typical designs have often considered that
the DNS server was usually located inside the protected domain, but
could be located outside of it. With encrypted DNS, the latter
option becomes plausible.
2. Terminology
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.
This document makes use of the terms defined in [RFC8499].
Also, this document makes use of the terms defined in [RFC7296]. In
particular, readers should be familiar with "initiator" and
"responder" terms used in that document.
This document makes use of the following terms:
'Do53': refers to unencrypted DNS.
'Encrypted DNS': refers to as scheme where DNS messages are sent
over an encrypted channel. Examples of encrypted DNS are DoT,
DoH, and DoQ.
'ENCDNS_IP*_*': refers to any IKEv2 Configuration Payload Attribute
Types defined in Section 4.
'ENCDNS_IP4_*': refers to an IKEv2 Configuration Payload Attribute
Type that carries one or multiple IPv4 addresses of an encrypted
DNS server.
'ENCDNS_IP6_*': refers to an IKEv2 Configuration Payload Attribute
Type that carries one or multiple IPv6 addresses of an encrypted
DNS server.
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3. Sample Deployment Scenarios
3.1. Roaming Enterprise Users
In this Enterprise scenario (Section 1.1.3 of [RFC7296]), a roaming
user connects to the Enterprise network through an IPsec tunnel. The
split-tunnel Virtual Private Network (VPN) configuration allows the
endpoint to access hosts that resides in the Enterprise network
[RFC8598] using that tunnel; other traffic not destined to the
Enterprise does not traverse the tunnel. In contrast, a non-split-
tunnel VPN configuration causes all traffic to traverse the tunnel
into the enterprise.
For both split- and non-split-tunnel configurations, the use of
encrypted DNS instead of Do53 provides privacy and integrity
protection along the entire path (rather than just to the VPN
termination device) and can communicate the encrypted DNS server
policies.
For split-tunnel VPN configurations, the endpoint uses the
Enterprise-provided encrypted DNS server to resolve internal-only
domain names.
For non-split-tunnel VPN configurations, the endpoint uses the
Enterprise-provided encrypted DNS server to resolve both internal and
external domain names.
Enterprise networks are susceptible to internal and external attacks.
To minimize that risk all enterprise traffic is encrypted
(Section 2.1 of [I-D.arkko-farrell-arch-model-t]).
3.2. VPN Service Provider
Legacy VPN service providers usually preserve end-users' data
confidentiality by sending all communication traffic through an
encrypted tunnel. A VPN service provider can also provide guarantees
about the security of the VPN network by filtering malware and
phishing domains.
Browsers and OSes support DoH/DoT; VPN providers may no longer expect
DNS clients to fallback to Do53 just because it is a closed network.
The encrypted DNS server hosted by the VPN service provider can be
securely discovered by the endpoint using the IKEv2 Configuration
Payload Attribute Type.
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3.3. DNS Offload
VPN service providers typically allow split-tunnel VPN configuration
in which users can choose applications that can be excluded from the
tunnel. For example, users may exclude applications that restrict
VPN access.
The encrypted DNS server hosted by the VPN service provider can be
securely discovered by the endpoint using the IKEv2 Configuration
Payload Attribute Type.
4. IKEv2 Configuration Payload Attribute Types for Encrypted DNS
4.1. ENCDNS_IP*_* Configuration Payload Attributes
The ENCDNS_IP*_* IKEv2 Configuration Payload Attribute Types are used
to configure a DoT, DoH, or DoQ DNS server. All these attributes
share the format shown in Figure 1.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-----------------------------+-------------------------------+
|R| Attribute Type | Length |
+-+-----------------------------+---------------+---------------+
| Port Number | RESERVED | Num Addresses |
+-------------------------------+---------------+---------------+
| |
~ IP Addresses ~
| |
+---------------------------------------------------------------+
| |
~ DNS Authentication Domain Name ~
| |
+---------------------------------------------------------------+
Figure 1: Attributes Format
The fields of the attribute shown in Figure 1 are as follows:
o R (Reserved, 1 bit) - This bit MUST be set to zero and MUST be
ignored on receipt (see Section 3.15.1 of [RFC7296] for details).
o Attribute Type (15 bits) - Identifier for Configuration Attribute
Type; is set to one of the TBA1-TBA6 values listed in Section 7.1.
o Length (2 octets, unsigned integer) - Length of the data in
octets. In particular, this field is set to:
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* 0 if the Configuration payload has types CFG_REQUEST or
CFG_ACK.
* (2 + Length of the ADN + N * 4) for ENCDNS_IP4_* attributes if
the Configuration payload of a has types CFG_REPLY or CFG_SET;
N being the number of included IPv4 addresses ('Num
addresses').
* (2 + Length of the ADN + N * 16) for ENCDNS_IP6_* attributes if
the Configuration payload has types CFG_REPLY or CFG_SET; N
being the number of included IPv6 addresses ('Num addresses').
o Port Number (2 octets, unsigned integer) - Indicates the port
number to be used for the encrypted DNS. As a reminder, the
default port number is 853 for DoT and 443 for DoH.
o RESERVED (1 octet) - These bits are reserved for future use.
These bits MUST be set to zero by the sender and MUST be ignored
by the receiver.
o Num Addresses (1 octet) - Indicates the number of enclosed IPv4
(for ENCDNS_IP4_* attribute types) or IPv6 (for ENCDNS_IP6_*
attribute types) addresses.
o IP Address(es) (variable) - One or more IPv4 or IPv6 addresses to
be used to reach the encrypted DNS identified by the name in the
DNS Authentication Domain Name.
o Authentication Domain Name (variable) - A fully qualified domain
name of the DoT, DoH, or DoQ DNS server following the syntax
defined in [RFC5890]. The name MUST NOT contain any terminators
(e.g., NULL, CR).
An example of valid ADN for DoH server is "doh1.example.com".
4.2. ENCDNS_URI_TEMPLATE Configuration Payload Attribute
DoH servers may support more than one URI Template [RFC8484]. Also,
if the resolver hosts several DoH services (e.g., no-filtering,
blocking adult content, blocking malware), these services can be
discovered as templates.
Figure 2 depictes the format of the ENCDNS_URI_TEMPLATE IKEv2
Configuration Payload Attribute Type whihc is used to configure DoH
URI Template(s).
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-----------------------------+-------------------------------+
|R| ENCDNS_URI_TEMPLATE | Length |
+-+-----------------------------+---------------+---------------+
| |
~ uri-template-data ~
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Each instance of the uri-template-data is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
| uri-template-len | URI Template |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+-+-+-+-+-+
Figure 2: DoH URI Template Attribute Format
The fields of the attribute shown in Figure 2 are as follows:
o R (Reserved, 1 bit) - This bit MUST be set to zero and MUST be
ignored on receipt (see Section 3.15.1 of [RFC7296] for details).
o Attribute Type (15 bits) - Identifier for Configuration Attribute
Type; is set to ENCDNS_URI_TEMPLATE (TBA7) (see Section 7.1).
o Length (2 octets, unsigned integer) - Length of the data in
octets. In particular, this field is set to '0' if the
Configuration payload has types CFG_REQUEST or CFG_ACK.
o uri-template-data (variable) - XXXX.
An example of valid URI Template is "XXXX".
How a DoH client makes use of the configured DoH services is out of
the scope of this document.
5. IKEv2 Protocol Exchange
This section describes how an initiator can be configured with an
encrypted DNS server (e.g., DoH, DoT) using IKEv2.
Initiators indicate the support of an encrypted DNS in the
CFG_REQUEST payloads by including one or multiple ENCDNS_IP*_*
attributes, while responders supply the encrypted DNS configuration
in the CFG_REPLY payloads. Concretely:
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If the initiator supports encrypted DNS, it includes one or more
ENCDNS_IP*_* attributes in the CFG_REQUEST with the "Attribute
Type" set to the requested encrypted DNS type (Section 4). For
each supported encrypted DNS type the initiator MUST include
exactly one attribute with the Length field set to 0, so that no
data is included for these attributes. If DoH is requested, the
initiator includes also ENCDNS_URI_TEMPLATE in the CFG_REQUEST
with "Length" set to 0.
For each ENCDNS_IP*_* attribute from the CFG_REQUEST, if the
responder supports the corresponding encrypted DNS type, and
absent any policy, the responder sends back an ENCDNS_IP*_*
attribute in the CFG_REPLY with this encrypted DNS type and an
appropriate list of IP addresses, a port number, and an ADN. The
list of IP addresses MUST NOT be empty. Multiple instances of the
same ENCDNS_IP*_* attribute MAY be returned if distinct ADNs (or
port numbers) are to be returned by the responder. If the
responder includes ENCDNS_IP4_DOH or ENCDNS_IP6_DOH in the
response, it MUST also include ENCDNS_URI_TEMPLATE carrying one or
more URI Templates.
If the CFG_REQUEST includes an ENCDNS_IP*_* attribute but the
CFG_REPLY does not include an ENCDNS_IP*_* matching the requested
encrypted DNS type, this is an indication that requested encrypted
DNS type(s) is not supported by the responder or the responder is
not configured to provide corresponding server addresses.
The behavior of the responder if it receives both ENCDNS_IP*_* and
INTERNAL_IP6_DNS (or INTERNAL_IP4_DNS) attributes is policy-based
and deployment-specific. However, it is RECOMMENDED that if the
responder includes at least one ENCDNS_IP*_* attribute in the
reply, it should not include any of INTERNAL_IP4_DNS/
INTERNAL_IP6_DNS attributes.
The DNS client establishes an encrypted DNS session (e.g., DoT, DoH,
DoQ) with the address(es) conveyed in ENCDNS_IP*_* and uses the
mechanism discussed in Section 8 of [RFC8310] to authenticate the DNS
server certificate using the authentication domain name conveyed in
ENCDNS_IP*_*.
If the IPsec connection is a split-tunnel configuration and the
initiator negotiated INTERNAL_DNS_DOMAIN as per [RFC8598], the DNS
client MUST resolve the internal names using ENCDNS_IP*_* DNS
servers.
Note: [RFC8598] requires INTERNAL_IP6_DNS (or INTERNAL_IP4_DNS)
attribute to be mandatory present when INTERNAL_DNS_DOMAIN is
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included. This specification relaxes that constraint in the
presence of ENCDNS_IP*_* attributes.
6. Security Considerations
This document adheres to the security considerations defined in
[RFC7296]. In particular, this document does not alter the trust on
the DNS configuration provided by a responder.
Networks are susceptible to internal attacks as discussed in
Section 3.2 of [I-D.arkko-farrell-arch-model-t]. Hosting encrypted
DNS server even in case of split-VPN configuration minimizes the
attack vector (e.g., a compromised network device cannot monitor/
modify DNS traffic). This specification describes a mechanism to
restrict access to the DNS messages to only the parties that need to
know.
The initiator may trust the encrypted DNS servers supplied by means
of IKEv2 from a trusted responder more than the locally provided DNS
servers, especially in the case of connecting to unknown or untrusted
networks (e.g., coffee shops or hotel networks).
If IKEv2 responder has used NULL Authentication method [RFC7619] to
authenticate itself, the initiator MUST NOT use returned ENCDNS_IP*_*
servers configuration unless it is pre-configured in the OS or the
browser.
This specification does not extend the scope of accepting DNSSEC
trust anchors beyond the usage guidelines defined in Section 6 of
[RFC8598].
7. IANA Considerations
7.1. Configuration Payload Attribute Types
This document requests IANA to assign the following new IKEv2
Configuration Payload Attribute Types from the "IKEv2 Configuration
Payload Attribute Types" namespace available at
https://www.iana.org/assignments/ikev2-parameters/
ikev2-parameters.xhtml#ikev2-parameters-21.
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Multi-
Value Attribute Type Valued Length Reference
------ ------------------- ------ ---------- ------------
TBA1 ENCDNS_IP4_DOT YES 0 or more RFC XXXX
TBA2 ENCDNS_IP6_DOT YES 0 or more RFC XXXX
TBA3 ENCDNS_IP4_DOH YES 0 or more RFC XXXX
TBA4 ENCDNS_IP6_DOH YES 0 or more RFC XXXX
TBA5 ENCDNS_IP4_DOQ YES 0 or more RFC XXXX
TBA6 ENCDNS_IP6_DOQ YES 0 or more RFC XXXX
TBA7 ENCDNS_URI_TEMPLATE YES 0 or more RFC XXXX
8. Acknowledgements
Many thanks to Yoav Nir, Christian Jacquenet, Paul Wouters, and Tommy
Pauly for the review and comments.
Yoav and Paul suggested the use of one single attribute carrying both
the name and an IP address instead of depending on the existing
INTERNAL_IP6_DNS and INTERNAL_IP4_DNS attributes.
Christian Huitema suiggested to return a port number in the
attributes.
9. References
9.1. 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>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[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>.
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[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
9.2. Informative References
[I-D.arkko-farrell-arch-model-t]
Arkko, J. and S. Farrell, "Challenges and Changes in the
Internet Threat Model", draft-arkko-farrell-arch-model-
t-04 (work in progress), July 2020.
[I-D.ietf-dprive-dnsoquic]
Huitema, C., Mankin, A., and S. Dickinson, "Specification
of DNS over Dedicated QUIC Connections", draft-ietf-
dprive-dnsoquic-01 (work in progress), October 2020.
[RFC7619] Smyslov, V. and P. Wouters, "The NULL Authentication
Method in the Internet Key Exchange Protocol Version 2
(IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015,
<https://www.rfc-editor.org/info/rfc7619>.
[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>.
[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>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8598] Pauly, T. and P. Wouters, "Split DNS Configuration for the
Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 8598, DOI 10.17487/RFC8598, May 2019,
<https://www.rfc-editor.org/info/rfc8598>.
Authors' Addresses
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: TirumaleswarReddy_Konda@McAfee.com
Dan Wing
Citrix Systems, Inc.
USA
Email: dwing-ietf@fuggles.com
Valery Smyslov
ELVIS-PLUS
RU
Email: svan@elvis.ru
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