Internet DRAFT - draft-grover-add-policy-detection
draft-grover-add-policy-detection
Network Working Group A. Grover
Internet-Draft P. Saint-Andre
Intended status: Standards Track Mozilla
Expires: January 9, 2020 July 8, 2019
DNS Resolver-Based Policy Detection Domain
draft-grover-add-policy-detection-00
Abstract
This document specifies the behavior that is expected from the Domain
Name System with regard to DNS queries for the special-use domain
name 'TBD.arpa' and designates this domain as a special-use domain
name.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Design Goals and Constraints . . . . . . . . . . . . . . . . 3
4. Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Domain Name Reservation Considerations . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Content-control software can be used to filter (i.e., block) web
requests that the user, the user's guardian, or the network operator
deems objectionable or outside the usage policy of the network.
Blocked resource categories can include advertisements, explicit
content, known malware, and government-unapproved material, along
with many others.
One way to implement content control that does not rely on software
or settings on the end-user's computing device is DNS-based content
filtering, which examines a client's initial DNS request for the
domain providing a resource and then either returns no result or
returns an alternate result so that the user is presented with an
explanation that filtering has taken place.
DNS-based policy such as content filtering is often built into a
network's configured DNS recursive resolver. In addition to blocking
a request, the resolver may also log the request for use by the
network administrators.
A network operator might wish to provide, or might be obligated to
provide, a filtering policy to users of its network. Because such a
policy is often enforced by the network operator's default resolver,
the use of a technology such as DNS over HTTPS (DoH) [RFC8484] or DNS
over TLS (DoT) [RFC7858] can result in bypassing local policies. If
the user agent can check for the presence of a policy, this could be
used as a signal that the network operator wishes its resolver to be
used as a condition of using the network, and that DoH or DoT should
be disabled.
At present, there is no standardized mechanism for the user or user
agent to identify the presence of a policy on a network's default
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resolver without making a request that could trigger the policy and
logging thereof, which could have undesirable side-effects.
Therefore, this document defines such a mechanism by defining a so-
called "canary domain" that is an instance of Special-Use Domain
Names [RFC6761]. DNS requests for this domain would return different
results when a DNS-based policy is in place, allowing for the
detection of the policy in a consistent way by user agents.
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.
3. Design Goals and Constraints
This canary domain has been defined with the following design goals
and constraints in mind:
o Minimize the risk of exposing personal information
o Ensure that the canary request cannot be mistaken for a user-
initiated DNS request
o Ensure that the technique is not specific to any given user agent,
policy, or resolver service
o Ensure that the technique is easy to implement for user agents and
resolvers
4. Behavior
Resolvers implementing a policy modify the result for the reserved
domain 'TBD.arpa', which can be observed by clients to determine if a
policy is present.
If a policy exists, the resolver MUST return NXDOMAIN [RFC1035]. If
policy is not present, DNS lookup will be successful (i.e., not
NXDOMAIN). (This could perhaps resolve to an actual host with a web
page managed by IANA, similar to example.com [RFC6761].)
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5. Domain Name Reservation Considerations
This section specifies considerations for systems involved in domain
name resolution when resolving queries for the reserved domain
'TBD.arpa', in accordance with [RFC6761].
1. Users: Users may invoke command-line DNS lookup tools to resolve
the domain, for the purposes of determining if a DNS-based policy
is present.
2. Application Software: Application software doing automated
lookups are the primary targets of this domain name reservation.
Applications can attempt to resolve this name in order to
determine if a DNS-based policy is present.
3. Name Resolution APIs and Libraries: Caching servers MUST NOT
treat this name as special, unless they implement a policy, in
which case they MUST return NXDOMAIN.
4. Caching DNS Servers: Caching servers MUST NOT treat this name as
special, unless they implement a policy, in which case they MUST
return NXDOMAIN.
5. Authoritative DNS Servers: Authoritative servers other than those
supporting the '.arpa' TLD MUST respond to queries for this name
with NXDOMAIN.
6. DNS Server Operators: Operators SHOULD ensure that any caching
DNS server with a policy on their network properly responds to
this name with NXDOMAIN.
7. DNS Registries/Registrars: The defined name is a subdomain of the
'.arpa' top-level domain, which is operated by IANA under the
authority of the Internet Architecture Board according to the
rules established in [RFC3172]. There are no other registrars
for '.arpa'.
6. IANA Considerations
IANA is requested to record the domain name 'TBD.arpa' in the
"Special-Use Domain Names" registry. See Section 5 for the completed
registration template.
[[NOTE TO RFC EDITOR: please change `TBD` to the name assigned by
IANA. The name 'dns-content-policy-detection' is suggested.]]
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7. Security Considerations
Although a DNS resolution request for the 'TBD.arpa' domain can
reveal whether the user or application wishes to detect the presence
of DNS-based policy, such a request is relatively neutral compared to
a request for a domain that might be subject to a policy.
8. References
8.1. Normative References
[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>.
[RFC3172] Huston, G., Ed., "Management Guidelines & Operational
Requirements for the Address and Routing Parameter Area
Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
September 2001, <https://www.rfc-editor.org/info/rfc3172>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[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>.
8.2. Informative References
[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>.
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Appendix A. Acknowledgements
Thanks to Martin Thomson for his feedback.
Authors' Addresses
Andy Grover
Mozilla
Email: agrover@mozilla.com
URI: https://mozilla.com/
Peter Saint-Andre
Mozilla
Phone: +1 720 256 6756
Email: stpeter@mozilla.com
URI: https://mozilla.com/
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