RFC 6891 - Extension Mechanisms for DNS (EDNS(0))

Request for Comments: 6891
STD: 75
Obsoletes: 2671, 2673
Category: Standards Track
ISSN: 2070-1721

Authors:

• J. Damas (Bond Internet Systems)
• M. Graff
• P. Vixie (Internet Systems Consortium)

Date: April 2013

Abstract

The Domain Name System's wire protocol includes a number of fixed fields whose range has been or soon will be exhausted and does not allow requestors to advertise their capabilities to responders. This document describes backward-compatible mechanisms for allowing the protocol to grow.

This document updates the Extension Mechanisms for DNS (EDNS(0)) specification (and obsoletes RFC 2671) based on feedback from deployment experience in several implementations. It also obsoletes RFC 2673 ("Binary Labels in the Domain Name System") and adds considerations on the use of extended labels in the DNS.

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 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6891.

Copyright Notice

Copyright (c) 2013 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Contents

• 1. Introduction
• 2. Terminology
• 3. EDNS Support Requirement
• 4. DNS Message Changes
  • 4.1. Message Header
  • 4.2. Label Types
  • 4.3. UDP Message Size
• 5. Extended Label Types
• 6. The OPT Pseudo-RR
  • 6.1. OPT Record Definition
    • 6.1.1. Basic Elements
    • 6.1.2. Wire Format
    • 6.1.3. OPT Record TTL Field Use
    • 6.1.4. Flags
  • 6.2. Behaviour
    • 6.2.1. Cache Behaviour
    • 6.2.2. Fallback
    • 6.2.3. Requestor's Payload Size
    • 6.2.4. Responder's Payload Size
    • 6.2.5. Payload Size Selection
    • 6.2.6. Support in Middleboxes
• 7. Transport Considerations
• 8. Security Considerations
• 9. IANA Considerations
  • 9.1. OPT Option Code Allocation Procedure
• 10. References
  • 10.1. Normative References
  • 10.2. Informative References
• Appendix A. Changes since RFCs 2671 and 2673