Internet DRAFT - draft-pusateri-dhc-dns-driu
draft-pusateri-dhc-dns-driu
Internet Engineering Task Force T. Pusateri
Internet-Draft Unaffiliated
Intended status: Informational W. Toorop
Expires: January 3, 2019 NLnet Labs
July 2, 2018
DHCPv6 Options for private DNS Discovery
draft-pusateri-dhc-dns-driu-00
Abstract
This draft provides a series of DHCPv6 options for a DHCPv6 client to
request from a DHCPv6 server to aid in configuring DNS servers that
support private requests/responses.
Status of This Memo
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Copyright (c) 2018 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Trust . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DHCPv6 Encapsulating Options . . . . . . . . . . . . . . . . 3
4. DHCPv6 DNS over TLS Encapsulated Options . . . . . . . . . . 5
4.1. IPv6 Address Option . . . . . . . . . . . . . . . . . . . 5
4.2. ADN Option . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Port Option . . . . . . . . . . . . . . . . . . . . . . . 6
5. DHCPv6 DNS over DTLS Encapsulated Options . . . . . . . . . . 7
6. DHCPv6 DNS over HTTPS (DoH) Encapsulated Options . . . . . . 7
6.1. URI Option . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. ISC DHCPv6 Configuration Example . . . . . . . . . . 11
A.1. ISC DHCPv6 Server Configuration . . . . . . . . . . . . . 11
A.2. ISC DHCPv6 Client Configuration . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
There are three standardized forms for providing privacy to DNS
including DNS over TLS (as defined in [RFC7858]), DNS over DTLS (as
defined in [RFC8094]), and DNS over HTTPS (DoH) as defined in
[I-D.ietf-doh-dns-over-https]. In order to use these encrypted forms
of DNS securely, more information is needed by the client than the
DNS Server list defined in Section 3 of [RFC3646]. This document
defines three new DHCPv6 encapsulating options containing additional
DHCPv6 options for clients to configure secure DNS in one of these
forms. Each top level option specifies ONE server. Multiple servers
are specified by including multiple instances of the same top level
option with different encapsulated options.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Trust
Encrypting the DNS transport provides privacy of the information
contained in the DNS requests/responses across the connection. It
does not provide privacy at the endpoints of the connection. The
private DNS configuration parameters obtained by a client via DHCPv6
are not automatically trusted. Trust is established in many ways or
not at all. The environment a client finds itself in will determine
how trustworthy the DHCPv6 reply may or may not be. There should be
no false sense of privacy derived from the presence of these options
in a DHCPv6 reply.
The following points may assist the DHCPv6 client:
1. clients can choose whether or not to use the DNS server
configuration parameters they receive via DHCPv6 and may simply
override these parameters with their own configuration.
2. DHCPv6 servers already provide unencrypted DNS server parameters
to clients that are regularly used because the client has decided
to trust the server reply in that environment.
3. client implementations (or operating system vendors) could
establish whitelists (or blacklists) of known good (bad) servers.
4. the community could establish a registry of trusted DNS privacy
servers.
3. DHCPv6 Encapsulating Options
Encrypted DNS DHCPv6 configuration parameters will be encapsulated in
one or more of the following top level encapsulating options. These
options can be repeated as many times as necessary to configure a
list of secure DNS servers with one secure server per encapsulation.
This is permitted by Section 22 of [RFC3315]. There is no order
implied by the order of options sent or received. It is up to the
receiving client to determine which order to use the DNS server
configurations.
The format for the DNS over TLS [RFC7858] encapsulating option code
is:
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0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_DNS_TLS | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encapsulated-options (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DNS over TLS option
option-code: OPTION_DNS_TLS (TBD)
option-len: Length of the sum of the lengths of the encapsulated
options.
The format for the DNS over DTLS [RFC8094] encapsulating option code
is:
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_DNS_DTLS | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encapsulated-options (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DNS over DTLS option
option-code: OPTION_DNS_DTLS (TBD)
option-len: Length of the sum of the lengths of the encapsulated
options.
The format for the DNS over HTTPS [I-D.ietf-doh-dns-over-https]
encapsulating option code is:
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0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_DNS_HTTPS | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encapsulated-options (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: DNS over HTTPS option
option-code: OPTION_DNS_HTTPS (TBD)
option-len: Length of the sum of the lengths of the encapsulated
options.
4. DHCPv6 DNS over TLS Encapsulated Options
There are four possible DHCPv6 encapsulated options contained in a
top level OPTION_DNS_TLS option. Each sub-option MUST NOT appear
more than once within a top level option.
4.1. IPv6 Address Option
The first is an OPTION_IPV6 which is REQUIRED. This is a fixed
length and contains the IPv6 address of the server.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_IPV6 | option-length (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: IPv6 option
option-code: OPTION_IPV6 (TBD)
option-len: 16 bytes
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4.2. ADN Option
The second is OPTION_ADN. This is a variable length string
containing the Authentication Domain Name as specified in [RFC8310].
This name MUST be verified in accordance with [RFC6125] or subsequent
updates to this document. The client SHOULD send the Authenticated
Domain Name when establishing the TLS connection to the DNS server
using the TLS Server Name Indication (SNI) extension as defined in
Section 3 of [RFC6066]. The use of OPTION_ADN by the server is
OPTIONAL but strongly encouraged. The string is a DNS FQDN encoded
according to Section 3.1 of [RFC1035].
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ADN | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. server ADN .
. (variable length) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Server Name Indication option
option-code: OPTION_ADN (TBD)
option-len: Length of the encoded string
4.3. Port Option
The third option is OPTION_PORT. This is a fixed length option
containing the port number of the listening server. It defaults to
port 853 as defined in Section 3.1 of [RFC7858]. This DHCPv6 option
is OPTIONAL and there is no need to specify it when the server is
listening on port 853.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_PORT | option-length (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| port number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Port option
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option-code: OPTION_PORT (TBD)
option-len: 2 bytes
5. DHCPv6 DNS over DTLS Encapsulated Options
DNS over DTLS has the exact same set of possible DHCPv6 options as
DNS over TLS. The OPTION_IPV6 defined in Section 4.1 is REQUIRED.
OPTION_ADN defined in Section 4.2 is OPTIONAL. OPTION_PORT defined
in Section 4.3 is OPTIONAL. Please refer the these sections for
their definitions and descriptions.
6. DHCPv6 DNS over HTTPS (DoH) Encapsulated Options
The DNS over HTTPS top level OPTION_DNS_HTTPS encapsulation has only
one option defined at this time which is OPTION_URI. This option is
REQUIRED.
[[Q1: Should we allow OPTION_IPV6? --TJP]]
6.1. URI Option
OPTION_URI includes a server URI string that provides the necessary
components to connect to a DNS over HTTPS server as defined in
[I-D.ietf-doh-dns-over-https]. Note that the DNS over HTTPS
specification requires a server to respond to both GET and POST
methods. The URI MUST NOT include the query component beginning with
a "?" and including the "dns" variable that is used in a GET method
request. It is up to the client to decide whether to issue a GET or
POST method in the HTTP request. Therefore, the client is
responsible for appending the "?" and "dns" variable along with its
base64 encoded value to the URI for GET method HTTP requests.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_URI | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. server URI .
. (variable length) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: URI option
option-code: OPTION_URI (TBD)
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option-len: Length of server URI string
7. Security Considerations
Compromising domain name resolution may provide a way to direct
client network traffic to non-authentic service providers. Sending a
DNS client to a non-authentic DNS server could return DNS responses
with IPv6 addresses that do not represent the actual authoritative
AAAA records for the names queried but pretend to do so. Then
applications on the client computer would attempt to connect to the
server carrying out man-in-the-middle or trojan attacks. Before this
specification existed, DHCPv6 domain name servers could have directed
DHCPv6 clients to compromised DNS servers. Adding encrypted DNS
configuration parameters does not change this fact.
There are ways to verify the integrity of unencrypted DNS responses
using DNSSEC if a client begins with the root trust anchor. This
ensures the entire DNS root hasn't been replaced with a forgery.
In the same way, the integrity of the responses must still be
verified when the responses are received over an encrypted DNS
connection.
There are additional verification checks that can be done given the
additional parameters provided with these private DNS DHCPv6 options
to increase the likelihood a client is connecting to an authentic DNS
recursive resolver that are not possible if only the IPv6 address of
the DNS server is known:
1. When the ADN option is present, the client can use DNSSEC to
validate the address records for the DNS server and the matching
authentication domain name, followed by verifying the certificate
of the encrypted DNS Server through verification of the
corresponding TLSA records as described in DANE [RFC6698] and
updated in [RFC7671].
2. There is intentionally no option for the SPKI pin as defined in
[RFC7469] and usage as related to DNS as described in Section 4.2
of [RFC7858]. This is because there is no way for a client to
check the integrity of the pin when received from the network
operator via DHCPv6. The SPKI pin can still be used to validate
a private DNS server certificate but the SPKI pin must be
obtained out of band through a trusted method to be useful for
verification.
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8. IANA Considerations
This document identifies several new DHCPv6 Option Codes that require
an assigned number.
+------------------+-------------+-------------+
| Name | Option Code | Definition |
+------------------+-------------+-------------+
| OPTION_DNS_TLS | TBD | Section 3 |
| OPTION_DNS_DTLS | TBD | Section 3 |
| OPTION_DNS_HTTPS | TBD | Section 3 |
| OPTION_IPV6 | TBD | Section 4.1 |
| OPTION_ADN | TBD | Section 4.2 |
| OPTION_PORT | TBD | Section 4.3 |
| OPTION_URI | TBD | Section 6.1 |
+------------------+-------------+-------------+
Table 1
9. Acknowledgements
This document was motivated in part by Section 7.3.1 of [RFC8310].
Thanks to the authors Sara Dickinson, Daniel Kahn Gillmor, and
Tirumaleswar Reddy for documenting the issue. Thanks also to Ted
Lemon for appropriate warnings about this work.
10. References
10.1. Normative References
[I-D.ietf-doh-dns-over-https]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", draft-ietf-doh-dns-over-https-12 (work in
progress), June 2018.
[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>.
[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>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
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[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <https://www.rfc-editor.org/info/rfc7469>.
[RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based
Authentication of Named Entities (DANE) Protocol: Updates
and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
October 2015, <https://www.rfc-editor.org/info/rfc7671>.
[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>.
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/info/rfc8094>.
[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>.
10.2. Informative References
[RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
DOI 10.17487/RFC3646, December 2003,
<https://www.rfc-editor.org/info/rfc3646>.
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Appendix A. ISC DHCPv6 Configuration Example
The DHCPv6 options defined in this specification were tested with the
ISC DHCPv6 server _dhcpd_ and client _dhclient_ version 4.4.1. Using
this version, it was possible to send a single DNS over TLS
encapsulated option containing an IPv6 address, authentication domain
name, and port number. Multiple servers using multiple DNS over TLS
encapsulated options were not available via the client hooks script.
A.1. ISC DHCPv6 Server Configuration
option space tls;
option tls.ipv6 code 226 = ip6-address;
option tls.port code 227 = unsigned integer 16;
option tls.adn code 228 = domain-list;
option dhcp6.tls-encapsulation code 225 = encapsulate tls;
subnet6 2001:DB8:01::/64 {
option tls.ipv6 2a04:b900:0:100::37;
option tls.adn "getdnsapi.net";
option tls.ipv6 2620:fe::fe;
option tls.adn "dns.quad9.net";
}
A.2. ISC DHCPv6 Client Configuration
option space tls;
option tls.ipv6 code 226 = ip6-address;
option tls.port code 227 = unsigned integer 16;
option tls.adn code 228 = domain-list;
option dhcp6.tls-encapsulation code 225 = encapsulate tls;
request dhcp6.tls-encapsulation;
Authors' Addresses
Tom Pusateri
Unaffiliated
Raleigh, NC 27608
USA
Phone: +1 919 867 1330
Email: pusateri@bangj.com
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Willem Toorop
NLnet Labs
Science Park 400
Amsterdam 1098 XH
Netherlands
Email: willem@nlnetlabs.nl
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