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Learning About the Domain Name System (DNS) from its Terminology

  • Kazunori Fujiwara
  • Paul E. Hoffman
  • Andrew Sullivan
  • 11 Feb 2019

An RFC updating DNS terminology was recently published, continuing a decades-long IETF practice of publishing documents to help introduce interested readers to protocol topics by going through the most important terms.


The list of topics with terminology documents include general terminology (RFC 1983), network address translators (NATs) (RFC 2663), Diffserv (RFC 3260), Internet connectivity (RFC 4084), internationalization (RFC 6365), and Internet of Things (IoT) networks (RFC 7228). Although these documents are not meant to be step-by-step introductions to the topics, they help someone who already has some understanding go deeper into the topic, and often help clarify terms that are often misused in common writing.

There are many dozens of RFCs defining the DNS, so the terminology is often hard to find. Some common terms such as "host name" are not defined in any RFCs; some are defined only by example; worse, some are defined differently in different RFCs. RFC 8499, "DNS Terminology", was published as an update to an earlier work to address these issues.

This document is the result of long discussions in the Domain Name System Operations (DNSOPS) Working Group, where dozens of DNS operators, software developers, and other experts brought up terms to be covered and argued over the current meaning of terms that are more than 30 years old. A common glossary is necessary to operate the DNS, and to continue to develop the DNS, so that people know what each other mean. The Working Group also hoped that the document would be useful to people who used the DNS tangentially, such as developers of other protocols and non-technical people who interact with the DNS in their work.

RFC 8499 is an update to the first DNS terminology document, RFC 7719. While the first document was being written, the WG agreed that some definitions (such as for "domain name") needed more work, and it was so difficult to get consensus on other terms that they were left out. The new document is much more complete, and contains some common terms not covered in the earlier document, such as "recursive query", "lame delegation", and "split DNS".

Another significant addition to the document is the first definition of a standards-track document of "the global DNS" and "private DNS". Many people think they know what "the DNS" is but may not have a specific definition for it; these new terms helps get everyone using the same definitions. Overall, nearly 40 terms that are not defined in other RFCs are defined in this document. Of course, the DNS will continue to evolve, and new terminology may appear. RFC 8499 is stable, but it might be revised a few years down the road to add these new terms.


  • [1] RFC 1983
    Internet Users' Glossary

    There are many networking glossaries in existence. This glossary concentrates on terms which are specific to the Internet. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.

  • [2] RFC 2663
    IP Network Address Translator (NAT) Terminology and Considerations

    This document attempts to describe the operation of NAT devices and the associated considerations in general, and to define the terminology used to identify various flavors of NAT. This memo provides information for the Internet community.

    Pyda Srisuresh

  • [3] RFC 3260
    New Terminology and Clarifications for Diffserv

    This memo captures Diffserv working group agreements concerning new and improved terminology, and provides minor technical clarifications. It is intended to update RFC 2474, RFC 2475 and RFC 2597. When RFCs 2474 and 2597 advance on the standards track, and RFC 2475 is updated, it is intended th...

  • [4] RFC 4084
    Terminology for Describing Internet Connectivity

    As the Internet has evolved, many types of arrangements have been advertised and sold as "Internet connectivity". Because these may differ significantly in the capabilities they offer, the range of options, and the lack of any standard terminology, the effort to distinguish between these service...

    Dr. John C. Klensin

  • [5] RFC 6365
    Terminology Used in Internationalization in the IETF

    This document provides a list of terms used in the IETF when discussing internationalization. The purpose is to help frame discussions of internationalization in the various areas of the IETF and to help introduce the main concepts to IETF participants. This memo documents an Internet Best Curr...

    Paul E. Hoffman

  • [6] RFC 7228
    Terminology for Constrained-Node Networks

    The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks.

    Ari Keränen, Carsten Bormann

  • [7] RFC 8499
    DNS Terminology

    The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for m...

  • [8] Domain Name System Operations

    Domain Name System Operations