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.
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
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
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
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