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, 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).