Internet DRAFT - draft-manuben-svcb-testing-flag
draft-manuben-svcb-testing-flag
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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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.
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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