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A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)
RFC 1996

Document type: RFC - Proposed Standard (August 1996; No errata)
Updates RFC 1035
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Document shepherd: No shepherd assigned

IESG State: RFC 1996 (Proposed Standard)
Responsible AD: (None)
Send notices to: No addresses provided

Network Working Group                                           P. Vixie
Request for Comments: 1996                                           ISC
Updates: 1035                                                August 1996
Category: Standards Track

    A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This memo describes the NOTIFY opcode for DNS, by which a master
   server advises a set of slave servers that the master's data has been
   changed and that a query should be initiated to discover the new
   data.

1. Rationale and Scope

   1.1. Slow propagation of new and changed data in a DNS zone can be
   due to a zone's relatively long refresh times.  Longer refresh times
   are beneficial in that they reduce load on the master servers, but
   that benefit comes at the cost of long intervals of incoherence among
   authority servers whenever the zone is updated.

   1.2. The DNS NOTIFY transaction allows master servers to inform slave
   servers when the zone has changed -- an interrupt as opposed to poll
   model -- which it is hoped will reduce propagation delay while not
   unduly increasing the masters' load.  This specification only allows
   slaves to be notified of SOA RR changes, but the architechture of
   NOTIFY is intended to be extensible to other RR types.

   1.3. This document intentionally gives more definition to the roles
   of "Master," "Slave" and "Stealth" servers, their enumeration in NS
   RRs, and the SOA MNAME field.  In that sense, this document can be
   considered an addendum to [RFC1035].

Vixie                       Standards Track                     [Page 1]
RFC 1996                       DNS NOTIFY                    August 1996

2. Definitions and Invariants

   2.1. The following definitions are used in this document:

   Slave           an authoritative server which uses zone transfer to
                   retrieve the zone.  All slave servers are named in
                   the NS RRs for the zone.

   Master          any authoritative server configured to be the source
                   of zone transfer for one or more slave servers.

   Primary Master  master server at the root of the zone transfer
                   dependency graph.  The primary master is named in the
                   zone's SOA MNAME field and optionally by an NS RR.
                   There is by definition only one primary master server
                   per zone.

   Stealth         like a slave server except not listed in an NS RR for
                   the zone.  A stealth server, unless explicitly
                   configured to do otherwise, will set the AA bit in
                   responses and be capable of acting as a master.  A
                   stealth server will only be known by other servers if
                   they are given static configuration data indicating
                   its existence.

   Notify Set      set of servers to be notified of changes to some
                   zone.  Default is all servers named in the NS RRset,
                   except for any server also named in the SOA MNAME.
                   Some implementations will permit the name server
                   administrator to override this set or add elements to
                   it (such as, for example, stealth servers).

   2.2. The zone's servers must be organized into a dependency graph
   such that there is a primary master, and all other servers must use
   AXFR or IXFR either from the primary master or from some slave which
   is also a master.  No loops are permitted in the AXFR dependency
   graph.

3. NOTIFY Message

   3.1. When a master has updated one or more RRs in which slave servers
   may be interested, the master may send the changed RR's name, class,
   type, and optionally, new RDATA(s), to each known slave server using
   a best efforts protocol based on the NOTIFY opcode.

   3.2. NOTIFY uses the DNS Message Format, although it uses only a
   subset of the available fields.  Fields not otherwise described
   herein are to be filled with binary zero (0), and implementations

Vixie                       Standards Track                     [Page 2]
RFC 1996                       DNS NOTIFY                    August 1996

   must ignore all messages for which this is not the case.

   3.3. NOTIFY is similar to QUERY in that it has a request message with

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