The Role of Wildcards in the Domain Name System
RFC 4592

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Network Working Group                                           E. Lewis
Request for Comments: 4592                                       NeuStar
Updates: 1034, 2672                                            July 2006
Category: Standards Track

                         The Role of Wildcards
                       in the Domain Name System

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.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This is an update to the wildcard definition of RFC 1034.  The
   interaction with wildcards and CNAME is changed, an error condition
   is removed, and the words defining some concepts central to wildcards
   are changed.  The overall goal is not to change wildcards, but to
   refine the definition of RFC 1034.

Lewis                       Standards Track                     [Page 1]
RFC 4592                      DNSEXT WCARD                     July 2006

Table of Contents

   1. Introduction ....................................................3
      1.1. Motivation .................................................3
      1.2. The Original Definition ....................................3
      1.3. Roadmap to This Document ...................................4
           1.3.1. New Terms ...........................................5
           1.3.2. Changed Text ........................................5
           1.3.3. Considerations with Special Types ...................5
      1.4. Standards Terminology ......................................6
   2. Wildcard Syntax .................................................6
      2.1. Identifying a Wildcard .....................................6
           2.1.1. Wildcard Domain Name and Asterisk Label .............6
           2.1.2. Asterisks and Other Characters ......................7
           2.1.3. Non-terminal Wildcard Domain Names ..................7
      2.2. Existence Rules ............................................7
           2.2.1. An Example ..........................................8
           2.2.2. Empty Non-terminals .................................9
           2.2.3. Yet Another Definition of Existence ................10
      2.3. When Is a Wildcard Domain Name Not Special? ...............10
   3. Impact of a Wildcard Domain Name on a Response .................10
      3.1. Step 2 ....................................................11
      3.2. Step 3 ....................................................11
      3.3. Part 'c' ..................................................12
           3.3.1. Closest Encloser and the Source of Synthesis .......12
           3.3.2. Closest Encloser and Source of Synthesis Examples ..13
           3.3.3. Type Matching ......................................13
   4. Considerations with Special Types ..............................14
      4.1. SOA RRSet at a Wildcard Domain Name .......................14
      4.2. NS RRSet at a Wildcard Domain Name ........................14
           4.2.1. Discarded Notions ..................................15
      4.3. CNAME RRSet at a Wildcard Domain Name .....................16
      4.4. DNAME RRSet at a Wildcard Domain Name .....................16
      4.5. SRV RRSet at a Wildcard Domain Name .......................17
      4.6. DS RRSet at a Wildcard Domain Name ........................17
      4.7. NSEC RRSet at a Wildcard Domain Name ......................18
      4.8. RRSIG at a Wildcard Domain Name ...........................18
      4.9. Empty Non-terminal Wildcard Domain Name ...................18
   5. Security Considerations ........................................18
   6. References .....................................................18
      6.1. Normative References ......................................18
      6.2. Informative References ....................................19
   7. Others Contributing to the Document ............................19

Lewis                       Standards Track                     [Page 2]
RFC 4592                      DNSEXT WCARD                     July 2006

1.  Introduction

   In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the
   synthesis of answers from special resource records (RRs) called
   wildcards.  The definition in RFC 1034 is incomplete and has proven
   to be confusing.  This document describes the wildcard synthesis by
   adding to the discussion and making limited modifications.
   Modifications are made to close inconsistencies that have led to
   interoperability issues.  This description does not expand the
   service intended by the original definition.

   Staying within the spirit and style of the original documents, this