DNS encoding of network names and other types
RFC 1101

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Network Working Group                                     P. Mockapetris
Request for Comments: 1101                                           ISI
Updates: RFCs 1034, 1035                                      April 1989

             DNS Encoding of Network Names and Other Types

1. STATUS OF THIS MEMO

   This RFC proposes two extensions to the Domain Name System:

      - A specific method for entering and retrieving RRs which map
        between network names and numbers.

      - Ideas for a general method for describing mappings between
        arbitrary identifiers and numbers.

   The method for mapping between network names and addresses is a
   proposed standard, the ideas for a general method are experimental.

   This RFC assumes that the reader is familiar with the DNS [RFC 1034,
   RFC 1035] and its use.  The data shown is for pedagogical use and
   does not necessarily reflect the real Internet.

   Distribution of this memo is unlimited.

2. INTRODUCTION

   The DNS is extensible and can be used for a virtually unlimited
   number of data types, name spaces, etc.  New type definitions are
   occasionally necessary as are revisions or deletions of old types
   (e.g., MX replacement of MD and MF [RFC 974]), and changes described
   in [RFC 973].  This RFC describes changes due to the general need to
   map between identifiers and values, and a specific need for network
   name support.

   Users wish to be able to use the DNS to map between network names and
   numbers.  This need is the only capability found in HOSTS.TXT which
   is not available from the DNS.  In designing a method to do this,
   there were two major areas of concern:

      - Several tradeoffs involving control of network names, the
        syntax of network names, backward compatibility, etc.

      - A desire to create a method which would be sufficiently
        general to set a good precedent for future mappings,
        for example, between TCP-port names and numbers,

Mockapetris                                                     [Page 1]
RFC 1101     DNS Encoding of Network Names and Other Types    April 1989

        autonomous system names and numbers, X.500 Relative
        Distinguished Names (RDNs) and their servers, or whatever.

   It was impossible to reconcile these two areas of concern for network
   names because of the desire to unify network number support within
   existing IP address to host name support.  The existing support is
   the IN-ADDR.ARPA section of the DNS name space.  As a result this RFC
   describes one structure for network names which builds on the
   existing support for host names, and another family of structures for
   future yellow pages (YP) functions such as conversions between TCP-
   port numbers and mnemonics.

   Both structures are described in following sections.  Each structure
   has a discussion of design issues and specific structure
   recommendations.

   We wish to avoid defining structures and methods which can work but
   do not because of indifference or errors on the part of system
   administrators when maintaining the database.  The WKS RR is an
   example.  Thus, while we favor distribution as a general method, we
   also recognize that centrally maintained tables (such as HOSTS.TXT)
   are usually more consistent though less maintainable and timely.
   Hence we recommend both specific methods for mapping network names,
   addresses, and subnets, as well as an instance of the general method
   for mapping between allocated network numbers and network names.
   (Allocation is centrally performed by the SRI Network Information
   Center, aka the NIC).

3. NETWORK NAME ISSUES AND DISCUSSION

   The issues involved in the design were the definition of network name
   syntax, the mappings to be provided, and possible support for similar
   functions at the subnet level.

3.1. Network name syntax

   The current syntax for network names, as defined by [RFC 952] is an
   alphanumeric string of up to 24 characters, which begins with an
   alpha, and may include "." and "-" except as first and last
   characters.  This is the format which was also used for host names
   before the DNS.  Upward compatibility with existing names might be a
   goal of any new scheme.

   However, the present syntax has been used to define a flat name
   space, and hence would prohibit the same distributed name allocation
   method used for host names.  There is some sentiment for allowing the
   NIC to continue to allocate and regulate network names, much as it
   allocates numbers, but the majority opinion favors local control of

Mockapetris                                                     [Page 2]
RFC 1101     DNS Encoding of Network Names and Other Types    April 1989

   network names.  Although it would be possible to provide a flat space
   or a name space in which, for example, the last label of a domain
   name captured the old-style network name, any such approach would add