Extension Mechanisms for DNS (EDNS) EXPIRE Option
RFC 7314

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Independent Submission                                        M. Andrews
Request for Comments: 7314                                           ISC
Category: Experimental                                         July 2014
ISSN: 2070-1721

           Extension Mechanisms for DNS (EDNS) EXPIRE Option

Abstract

   This document specifies a method for secondary DNS servers to honour
   the SOA EXPIRE field as if they were always transferring from the
   primary, even when using other secondaries to perform indirect
   transfers and refresh queries.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This is a contribution to the RFC Series, independently
   of any other RFC stream.  The RFC Editor has chosen to publish this
   document at its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see 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/rfc7314.

Copyright Notice

   Copyright (c) 2014 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.

Andrews                       Experimental                      [Page 1]
RFC 7314    Extension Mechanisms for DNS (EDNS) EXPIRE Option  July 2014

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Reserved Words  . . . . . . . . . . . . . . . . . . . . .   2
   2.  Expire EDNS Option (Query)  . . . . . . . . . . . . . . . . .   3
   3.  Expire EDNS Option (Response) . . . . . . . . . . . . . . . .   3
     3.1.  Primary Server  . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Secondary Server  . . . . . . . . . . . . . . . . . . . .   3
     3.3.  Non-authoritative Server  . . . . . . . . . . . . . . . .   3
   4.  Secondary Behaviour . . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The expire field of a DNS zone's SOA record [RFC1035] is supposed to
   indicate when a secondary server shall discard the contents of the
   zone when it has been unable to contact the primary [RFC1034].
   Current practice only works when all the secondaries contact the
   primary directly to perform refresh queries and zone transfers.

   While secondaries are expected to be able to, and often are
   configured to, transfer from other secondaries for robustness reasons
   as well as reachability constraints, there is no mechanism provided
   to preserve the expiry behaviour when using a secondary.  Instead,
   secondaries have to know whether they are talking directly to the
   primary or another secondary and use that to decide whether or not to
   update the expire timer.  This, however, fails to take into account
   delays in transferring from one secondary to another.

   There are also zone-transfer graphs in which the secondary never
   talks to the primary, so the effective expiry period becomes
   multiplied by the length of the zone-transfer graph, which is
   infinite when it contains loops.

   This document provides a mechanism to preserve the expiry behaviour
   regardless of what zone-transfer graph is constructed and whether the
   secondary is talking to the primary or another secondary.

1.1.  Reserved Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

Andrews                       Experimental                      [Page 2]
RFC 7314    Extension Mechanisms for DNS (EDNS) EXPIRE Option  July 2014

2.  Expire EDNS Option (Query)

   The EDNS [RFC6891] EXPIRE option has the value <9>.  The EDNS EXPIRE
   option MAY be included on any QUERY, though usually this is only done
   on SOA, AXFR, and IXFR queries involved in zone maintenance.  This is
   done by adding a zero-length EDNS EXPIRE option to the options field
   of the OPT record when the query is made.

3.  Expire EDNS Option (Response)

3.1.  Primary Server

   When the query is directed to the primary server for the zone, the