RFC 9460 - Service Binding and Parameter Specification via the DNS (SVCB and HTTPS Resource Records)

Authors: B. Schwartz (Meta Platforms, Inc.), M. Bishop, E. Nygren (Akamai Technologies)
Date: November 2023
Category: Standards Track
ISSN: 2070-1721

Abstract

This document specifies the "SVCB" ("Service Binding") and "HTTPS" DNS resource record (RR) types to facilitate the lookup of information needed to make connections to network services, such as for HTTP origins. SVCB records allow a service to be provided from multiple alternative endpoints, each with associated parameters (such as transport protocol configuration), and are extensible to support future uses (such as keys for encrypting the TLS ClientHello). They also enable aliasing of apex domains, which is not possible with CNAME. The HTTPS RR is a variation of SVCB for use with HTTP (see RFC 9110, "HTTP Semantics"). By providing more information to the client before it attempts to establish a connection, these records offer potential benefits to both performance and privacy.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9460.

Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved.

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 and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Contents

• 1. Introduction
  • 1.1. Goals
  • 1.2. Overview of the SVCB RR
  • 1.3. Terminology
• 2. The SVCB Record Type
  • 2.1. Zone-File Presentation Format
  • 2.2. RDATA Wire Format
  • 2.3. SVCB Query Names
  • 2.4. Interpretation
  • 2.5. Special Handling of "." in TargetName
• 3. Client Behavior
  • 3.1. Handling Resolution Failures
  • 3.2. Clients Using a Proxy
• 4. DNS Server Behavior
  • 4.1. Authoritative Servers
  • 4.2. Recursive Resolvers
  • 4.3. General Requirements
  • 4.4. EDNS Client Subnet (ECS)
• 5. Performance Optimizations
  • 5.1. Optimistic Pre-connection and Connection Reuse
  • 5.2. Generating and Using Incomplete Responses
• 6. SVCB-Compatible RR Types
• 7. Initial SvcParamKeys
  • 7.1. "alpn" and "no-default-alpn"
  • 7.2. "port"
  • 7.3. "ipv4hint" and "ipv6hint"
  • 7.4. "mandatory"
• 8. ServiceMode RR Compatibility and Mandatory Keys
• 9. Using Service Bindings with HTTP
  • 9.1. Query Names for HTTPS RRs
  • 9.2. Comparison with Alt-Svc
  • 9.3. Interaction with Alt-Svc
  • 9.4. Requiring Server Name Indication
  • 9.5. HTTP Strict Transport Security (HSTS)
  • 9.6. Use of HTTPS RRs in Other Protocols
• 10. Zone Structures
  • 10.1. Structuring Zones for Flexibility
  • 10.2. Structuring Zones for Performance
  • 10.3. Operational Considerations
  • 10.4. Examples
• 11. Interaction with Other Standards
• 12. Security Considerations
• 13. Privacy Considerations
• 14. IANA Considerations
  • 14.1. SVCB RR Type
  • 14.2. HTTPS RR Type
  • 14.3. New Registry for Service Parameters
  • 14.4. Other Registry Updates
• 15. References
  • 15.1. Normative References
  • 15.2. Informative References
• Appendix A. Decoding Text in Zone Files
• Appendix B. HTTP Mapping Summary
• Appendix C. Comparison with Alternatives
• Appendix D. Test Vectors
• Acknowledgments and Related Proposals
• Authors' Addresses