Dynamic Updates in the Domain Name System (DNS UPDATE)
RFC 2136

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Network Working Group                                  P. Vixie, Editor
Request for Comments: 2136                                          ISC
Updates: 1035                                                S. Thomson
Category: Standards Track                                      Bellcore
                                                             Y. Rekhter
                                                                  Cisco
                                                               J. Bound
                                                                    DEC
                                                             April 1997

         Dynamic Updates in the Domain Name System (DNS UPDATE)

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

   The Domain Name System was originally designed to support queries of
   a statically configured database.  While the data was expected to
   change, the frequency of those changes was expected to be fairly low,
   and all updates were made as external edits to a zone's Master File.

   Using this specification of the UPDATE opcode, it is possible to add
   or delete RRs or RRsets from a specified zone.  Prerequisites are
   specified separately from update operations, and can specify a
   dependency upon either the previous existence or nonexistence of an
   RRset, or the existence of a single RR.

   UPDATE is atomic, i.e., all prerequisites must be satisfied or else
   no update operations will take place.  There are no data dependent
   error conditions defined after the prerequisites have been met.

1 - Definitions

   This document intentionally gives more definition to the roles of
   "Master," "Slave," and "Primary Master" servers, and their
   enumeration in NS RRs, and the SOA MNAME field.  In that sense, the
   following server type definitions can be considered an addendum to
   [RFC1035], and are intended to be consistent with [RFC1996]:

      Slave           an authoritative server that uses AXFR or IXFR to
                      retrieve the zone and is named in the zone's NS
                      RRset.

Vixie, et. al.              Standards Track                     [Page 1]
RFC 2136                       DNS Update                     April 1997

      Master          an authoritative server configured to be the
                      source of AXFR or IXFR data for one or more slave
                      servers.

      Primary Master  master server at the root of the AXFR/IXFR
                      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.

   A domain name identifies a node within the domain name space tree
   structure.  Each node has a set (possibly empty) of Resource Records
   (RRs).  All RRs having the same NAME, CLASS and TYPE are called a
   Resource Record Set (RRset).

   The pseudocode used in this document is for example purposes only.
   If it is found to disagree with the text, the text shall be
   considered authoritative.  If the text is found to be ambiguous, the
   pseudocode can be used to help resolve the ambiguity.

   1.1 - Comparison Rules

   1.1.1. Two RRs are considered equal if their NAME, CLASS, TYPE,
   RDLENGTH and RDATA fields are equal.  Note that the time-to-live
   (TTL) field is explicitly excluded from the comparison.

   1.1.2. The rules for comparison of character strings in names are
   specified in [RFC1035 2.3.3].

   1.1.3. Wildcarding is disabled.  That is, a wildcard ("*") in an
   update only matches a wildcard ("*") in the zone, and vice versa.

   1.1.4. Aliasing is disabled: A CNAME in the zone matches a CNAME in
   the update, and will not otherwise be followed.  All UPDATE
   operations are done on the basis of canonical names.

   1.1.5. The following RR types cannot be appended to an RRset.  If the
   following comparison rules are met, then an attempt to add the new RR
   will result in the replacement of the previous RR:

      SOA    compare only NAME, CLASS and TYPE -- it is not possible to
             have more than one SOA per zone, even if any of the data
             fields differ.

      WKS    compare only NAME, CLASS, TYPE, ADDRESS, and PROTOCOL
             -- only one WKS RR is possible for this tuple, even if the
             services masks differ.

Vixie, et. al.              Standards Track                     [Page 2]
RFC 2136                       DNS Update                     April 1997

      CNAME  compare only NAME, CLASS, and TYPE -- it is not possible