



Network Working Group                                            M. Pels
Internet-Draft                                                  F. Obser
Intended status: Standards Track                                RIPE NCC
Expires: 19 November 2026                                    18 May 2026


                    AXFR message type for DNS NOTIFY
                    draft-pels-dnsop-axfr-notify-00

Abstract

   This document defines a new AXFR message type for DNS NOTIFY
   messages.  The message instructs a secondary server to perform an
   AXFR zone transfer of a zone.

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   This Internet-Draft will expire on 19 November 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Protocol sequence . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Initiation  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Secondary server behaviour  . . . . . . . . . . . . . . .   3
   4.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   DNS NOTFY[RFC1996] describes a method to inform secondary name
   servers that a zone has changed.  Upon receipt of a NOTIFY(SOA)
   message, a secondary will query the primary server for the SOA of the
   zone, and perform an IXFR[RFC1995] or AXFR[RFC5936] zone transfer if
   the SOA SERIAL has been incremented since the last time the zone was
   fetched.

   There are cases when it is desirable to force a secondary server to
   perform an AXFR zone transfer.  Example scenarios are an incorrectly
   synchronized database on a secondary server due to a software bug, or
   an operator incidentally wanting to propagate changes to a zone
   without updating the SOA SERIAL.

   Most authoritative DNS server software supports performing a forced
   AXFR zone transfer.  However, this can only be initiated by the
   operator of the DNS server, and secondary servers for a zone may not
   be managed by the same operator as the primary server(s).  This
   document defines a new NOTIFY(AXFR) message type, used to initiate
   forced AXFR transfers by secondary servers from a primary server of a
   zone.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.







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3.  Protocol sequence

3.1.  Initiation

   When a primary server wants its secondary servers to perform an AXFR
   zone transfer, it sends a NOTIFY message with the following
   characteristics to each secondary server:

   query ID:   (new)
   op:         NOTIFY (4)
   resp:       NOERROR
   flags:      AA
   qcount:     1
   qname:      (zone name)
   qclass:     (zone class)
   qtype:      T_AXFR

3.2.  Secondary server behaviour

   When a secondary server receives a NOTIFY(AXFR) request from one of
   its locally designated primaries for the zone enclosing the given
   QNAME, with QTYPE=AXFR and QR=0, it SHOULD perform an AXFR zone
   transfer from one of its configured primary servers.  It will also
   send a NOTIFY response back to the NOTIFY request's source, with the
   following characteristics:

   query ID:   (same)
   op:         NOTIFY (4)
   resp:       NOERROR
   flags:      QR AA
   qcount:     1
   qname:      (zone name)
   qclass:     (zone class)
   qtype:      T_AXFR

   If the secondary server, for the zone enclosing the given QNAME, is
   configured as a primary server for other secondary servers, it MUST
   also send a NOTIFY(AXFR) request to each of its configured
   secondaries.  This ensures that an entire chain of secondary servers
   is synchronized in concert.

4.  IANA considerations

   This document has no IANA actions.







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5.  Security considerations

   A NOTIFY(AXFR) request with a forged IP/UDP source address can cause
   a secondary to send spurious AXFR requests to its primary servers,
   leading to a denial of service attack if the forged requests are sent
   very often.  To counter this, secondary servers MUST rate-limit how
   often they will request an AXFR from their primaries.

   If a primary server has many secondaries, requesting all of them to
   perform an AXFR simultaneously may cause the primary to become
   overloaded.  The sending out of NOTIFY(AXFR) requests to secondary
   servers SHOULD be splayed to reduce this thundering herd effect.

6.  Normative References

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,
              <https://www.rfc-editor.org/info/rfc1995>.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <https://www.rfc-editor.org/info/rfc1996>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.

7.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Appendix A.  Acknowledgements

   The authors would like to thank Anand Buddhdev for contributing ideas
   and feedback to this document.

Authors' Addresses

   Martin Pels
   RIPE NCC
   Netherlands



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   Email: mpels@ripe.net


   Florian Obser
   RIPE NCC
   Netherlands
   Email: fobser@ripe.net












































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