DNS Transport over TCP - Implementation Requirements
RFC 7766

Document Type RFC - Proposed Standard (March 2016; No errata)
Obsoletes RFC 5966
Last updated 2016-03-03
Replaces draft-dickinson-dnsop-5966-bis
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Tim Wicinski
Shepherd write-up Show (last changed 2015-11-01)
IESG IESG state RFC 7766 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Joel Jaeggli
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IC
Internet Engineering Task Force (IETF)                      J. Dickinson
Request for Comments: 7766                                  S. Dickinson
Obsoletes: 5966                                                  Sinodun
Updates: 1035, 1123                                            R. Bellis
Category: Standards Track                                            ISC
ISSN: 2070-1721                                                A. Mankin
                                                              D. Wessels
                                                           Verisign Labs
                                                              March 2016

          DNS Transport over TCP - Implementation Requirements

Abstract

   This document specifies the requirement for support of TCP as a
   transport protocol for DNS implementations and provides guidelines
   towards DNS-over-TCP performance on par with that of DNS-over-UDP.
   This document obsoletes RFC 5966 and therefore updates RFC 1035 and
   RFC 1123.

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/rfc7766.

Dickinson, et al.            Standards Track                    [Page 1]
RFC 7766                      DNS over TCP                    March 2016

Copyright Notice

   Copyright (c) 2016 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Terminology  . . . . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Transport Protocol Selection  . . . . . . . . . . . . . . . .   5
   6.  Connection Handling . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Current Practices . . . . . . . . . . . . . . . . . . . .   6
       6.1.1.  Clients . . . . . . . . . . . . . . . . . . . . . . .   7
       6.1.2.  Servers . . . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Recommendations . . . . . . . . . . . . . . . . . . . . .   8
       6.2.1.  Connection Reuse  . . . . . . . . . . . . . . . . . .   8
         6.2.1.1.  Query Pipelining  . . . . . . . . . . . . . . . .   8
       6.2.2.  Concurrent Connections  . . . . . . . . . . . . . . .   9
       6.2.3.  Idle Timeouts . . . . . . . . . . . . . . . . . . . .   9
       6.2.4.  Teardown  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Response Reordering . . . . . . . . . . . . . . . . . . . . .  10
   8.  TCP Message Length Field  . . . . . . . . . . . . . . . . . .  11
   9.  TCP Fast Open . . . . . . . . . . . . . . . . . . . . . . . .  11
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     11.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Summary of Advantages and Disadvantages to Using TCP
                for DNS  . . . . . . . . . . . . . . . . . . . . . .  16
   Appendix B.  Changes to RFC 5966  . . . . . . . . . . . . . . . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

Dickinson, et al.            Standards Track                    [Page 2]
RFC 7766                      DNS over TCP                    March 2016

1.  Introduction

   Most DNS [RFC1034] transactions take place over UDP [RFC768].  TCP
   [RFC793] is always used for full zone transfers (using AXFR) and is
   often used for messages whose sizes exceed the DNS protocol's
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