The "testing" flag for Service Binding (SVCB) Records
draft-manuben-svcb-testing-flag-00

Network Working Group                                     B. M. Schwartz
Internet-Draft                                               M. Bretelle
Intended status: Standards Track                    Meta Platforms, Inc.
Expires: 15 August 2024                                 12 February 2024

         The "testing" flag for Service Binding (SVCB) Records
                   draft-manuben-svcb-testing-flag-00

Abstract

   This draft defines a flag to mark a service endpoint as being
   potentially unreliable.  This flag may be useful when introducing new
   features that could have a negative impact on availability.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-manuben-svcb-testing-flag/.

   Source for this draft and an issue tracker can be found at
   https://github.com/bemasc/svcb-testing-flag.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 15 August 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Interaction with SvcPriority  . . . . . . . . . . . . . .   3
     3.2.  Example: Encrypted DNS Protocol . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Service Binding (SVCB) DNS record type [RFC9460], and SVCB-
   compatible types like HTTPS, convey a collection of endpoints that
   can provide a service, along with metadata about each of those
   endpoints.  This metadata can indicate protocol features that are
   available and supported on those endpoints.

   In most cases, advertising new features is unlikely to render the
   service unavailable.  Clients that are unaware of these features will
   ignore them, and clients that are aware will fall back to other SVCB
   records or other connection modes if the feature doesn't work.
   However, for security-enhancing features, this fallback behavior
   would create a loss of security against an active attacker, so it is
   generally not allowed.  Instead, if the feature does not work as
   expected, the client will "fail closed".  This behavior can make it
   challenging to deploy security-enhancing features, as the initial
   public deployment can create an outage if the service is
   misconfigured.

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   This document defines a new SVCB SvcParam to help service operators
   offer new security features.  By marking these features as still
   being tested, the operator advises the client to interpret problems
   as an accidental failure by the operator, not a malicious action by
   an active attacker.

2.  Conventions and Definitions

   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.  Specification

   The "testing" flag is a SvcParam that always has an empty value in
   presentation and wire format.  When present, this flag indicates that
   this ServiceMode record is subject to outages, and clients SHOULD NOT
   interpret connection failures as evidence of an active attack.

   Service owners SHOULD ensure that this flag is mandatory, either
   explicitly (by adding mandatory=testing to the SvcParams) or
   implicitly if this parameter is "automatically mandatory" for the
   protocol mapping.  Future protocol mappings SHOULD make this SvcParam
   "automatically mandatory".

3.1.  Interaction with SvcPriority

   Clients SHOULD NOT alter the priority of SVCB records based on the
   presence of the "testing" flag.  Deprioritizing SVCB records with
   this flag would result in little or no user traffic making use of the
   testing record, which would defeat the goal of validating that new
   features function correctly for real users.

3.2.  Example: Encrypted DNS Protocol

   Consider the case of a plaintext DNS server operator at
   "dns.example.com" who would like to announce support for DNS over TLS
   [RFC7858].  Per [RFC9461], this operator could publish a record like:

   _dns.dns.example.com. SVCB 1 . alpn=dot

   Clients following [RFC9461] would retrieve this record, observe that
   DNS over TLS is available, and attempt to use it on TCP port 853.  If
   the TLS session cannot be established for any reason, a compliant
   client will not fall back to plaintext DNS on UDP port 53, because
   the failure could indicate an active attack ([RFC9461], Section 8.2).

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   If the operator of "dns.example.com" does not have operational
   confidence in their DNS over TLS service, this failure mode could
   raise concerns about the potential consequences of offering this new
   service.

   To reduce the risk associated with this new service, the operator
   could instead use the new "testing" flag as follows:

   _dns.dns.example.com. SVCB 1 . alpn=dot testing mandatory=testing

   Clients that do not implement this specification will ignore the
   record because it specifies an unrecognized mandatory SvcParam.  They
   will continue to use plaintext DNS.  Clients that respect the
   "testing" flag will attempt to use DNS over TLS, but they will fall
   back to plaintext DNS if DNS over TLS is non-functional.

4.  Security Considerations

   Use of the "testing" flag explicitly disables SVCB's defense against
   active attackers.  This is a loss in security.  However, the intent
   of this flag is to facilitate the deployment of security-enhancing
   protocols.  Downgrade-resistant security is achieved only when the
   testing period is complete and the "testing" flag is removed.

5.  IANA Considerations

   IANA is requested to add this entry to the SVCB SvcParams Registry:

   +========+=========+===============+===================+===========+
   | Number | Name    | Meaning       | Change Controller | Reference |
   +========+=========+===============+===================+===========+
   | TBD    | testing | Endpoint may  | IETF              | (This     |
   |        |         | be unreliable |                   | document) |
   +--------+---------+---------------+-------------------+-----------+

                                 Table 1

6.  References

6.1.  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/rfc/rfc2119>.

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   [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/rfc/rfc8174>.

   [RFC9460]  Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
              and Parameter Specification via the DNS (SVCB and HTTPS
              Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
              November 2023, <https://www.rfc-editor.org/rfc/rfc9460>.

6.2.  Informative References

   [I-D.dnsop-deleg]
              April, T., Špaček, P., Weber, R., and Lawrence,
              "Extensible Delegation for DNS", Work in Progress,
              Internet-Draft, draft-dnsop-deleg-00, 23 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-dnsop-deleg-
              00>.

   [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/rfc/rfc7858>.

   [RFC9461]  Schwartz, B., "Service Binding Mapping for DNS Servers",
              RFC 9461, DOI 10.17487/RFC9461, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9461>.

Acknowledgments

   This proposal is inspired by deployment considerations related to
   [I-D.dnsop-deleg].

Authors' Addresses

   Benjamin M. Schwartz
   Meta Platforms, Inc.
   Email: ietf@bemasc.net

   Manu Bretelle
   Meta Platforms, Inc.
   Email: chantr4@gmail.com

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