RFC 2915 (rfc2915) - Page 2 of 18

The Naming Authority Pointer (NAPTR) DNS Resource Record

RFC 2915                      NAPTR DNS RR                September 2000


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  NAPTR RR Format  . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Substitution Expression Grammar  . . . . . . . . . . . . . .   7
   4.  The Basic NAPTR Algorithm  . . . . . . . . . . . . . . . . .   8
   5.  Concerning How NAPTR Uses SRV Records  . . . . . . . . . . .   9
   6.  Application Specifications . . . . . . . . . . . . . . . . .  10
   7.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.1 Example 1  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.2 Example 2  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.3 Example 3  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  DNS Packet Format  . . . . . . . . . . . . . . . . . . . . .  13
   9.  Master File Format . . . . . . . . . . . . . . . . . . . . .  14
   10. Advice for DNS Administrators  . . . . . . . . . . . . . . .  14
   11. Notes  . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . .  15
   13. Security Considerations  . . . . . . . . . . . . . . . . . .  15
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  16
       References . . . . . . . . . . . . . . . . . . . . . . . . .  16
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  17
       Full Copyright Statement . . . . . . . . . . . . . . . . . .  18

1. Introduction

   This RR was originally produced by the URN Working Group [3] as a way
   to encode rule-sets in DNS so that the delegated sections of a URI
   could be decomposed in such a way that they could be changed and re-
   delegated over time.  The result was a Resource Record that included
   a regular expression that would be used by a client program to
   rewrite a string into a domain name.  Regular expressions were chosen
   for their compactness to expressivity ratio allowing for a great deal
   of information to be encoded in a rather small DNS packet.

   The function of rewriting a string according to the rules in a record
   has usefulness in several different applications.  This document
   defines the basic assumptions to which all of those applications must
   adhere to.  It does not define the reasons the rewrite is used, what
   the expected outcomes are, or what they are used for.  Those are
   specified by applications that define how they use the NAPTR record
   and algorithms within their contexts.

   Flags and other fields are also specified in the RR to control the
   rewrite procedure in various ways or to provide information on how to
   communicate with the host at the domain name that was the result of
   the rewrite.





Mealling & Daniel           Standards Track