The edns-tcp-keepalive EDNS0 Option
RFC 7828

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Internet Engineering Task Force (IETF)                        P. Wouters
Request for Comments: 7828                                       Red Hat
Category: Standards Track                                       J. Abley
ISSN: 2070-1721                                                Dyn, Inc.
                                                            S. Dickinson
                                                                 Sinodun
                                                               R. Bellis
                                                                     ISC
                                                              April 2016

                  The edns-tcp-keepalive EDNS0 Option

Abstract

   DNS messages between clients and servers may be received over either
   UDP or TCP.  UDP transport involves keeping less state on a busy
   server, but can cause truncation and retries over TCP.  Additionally,
   UDP can be exploited for reflection attacks.  Using TCP would reduce
   retransmits and amplification.  However, clients commonly use TCP
   only for retries and servers typically use idle timeouts on the order
   of seconds.

   This document defines an EDNS0 option ("edns-tcp-keepalive") that
   allows DNS servers to signal a variable idle timeout.  This
   signalling encourages the use of long-lived TCP connections by
   allowing the state associated with TCP transport to be managed
   effectively with minimal impact on the DNS transaction time.

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/rfc7828.

Wouters, et al.              Standards Track                    [Page 1]
RFC 7828           The edns-tcp-keepalive EDNS0 Option        April 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 Notation . . . . . . . . . . . . . . . . . . . .   4
   3.  The edns-tcp-keepalive Option . . . . . . . . . . . . . . . .   5
     3.1.  Option Format . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Use by DNS Clients  . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Sending Queries . . . . . . . . . . . . . . . . . . .   5
       3.2.2.  Receiving Responses . . . . . . . . . . . . . . . . .   6
     3.3.  Use by DNS Servers  . . . . . . . . . . . . . . . . . . .   6
       3.3.1.  Receiving Queries . . . . . . . . . . . . . . . . . .   6
       3.3.2.  Sending Responses . . . . . . . . . . . . . . . . . .   6
     3.4.  TCP Session Management  . . . . . . . . . . . . . . . . .   7
     3.5.  Non-clean Paths . . . . . . . . . . . . . . . . . . . . .   8
     3.6.  Anycast Considerations  . . . . . . . . . . . . . . . . .   8
   4.  Intermediary Considerations . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

Wouters, et al.              Standards Track                    [Page 2]
RFC 7828           The edns-tcp-keepalive EDNS0 Option        April 2016

1.  Introduction

   DNS messages between clients and servers may be received over either
   UDP or TCP [RFC1035].  Historically, DNS clients used APIs that only
   facilitated sending and receiving a single query over either UDP or
   TCP.  New APIs and deployment of DNSSEC validating resolvers on hosts
   that in the past were using stub resolving only is increasing the DNS