The Domain Name System Specified

The Domain Name System (DNS) is the Internet's distributed directory: it turns names such as example.com into the numeric addresses that machines use, without any single computer holding the whole list. It was invented by Paul Mockapetris at the University of Southern California's Information Sciences Institute (ISI) and published in November 1983 as two documents, RFC 882 (concepts and facilities) and RFC 883 (implementation and specification). The design was revised in November 1987 as RFC 1034 and RFC 1035, which remain the core of DNS today. The familiar top-level domains came separately: .com, .edu, .gov, .mil and .org were laid down by Jon Postel and J. Reynolds in RFC 920 in October 1984.

The problem: one file for the whole network

Before DNS, every host on the ARPANET learned every other host's name from the same place. Hosts were registered with the Network Information Center (NIC) at SRI, and the list was kept as a single table, the file HOSTS.TXT on the SRI-NIC machine. RFC 882 put the difficulty in one sentence: "The size of this table, and especially the frequency of updates to the table are near the limit of manageability."

RFC 1034, written four years later with hindsight, explained why. Every host fetched the file by FTP, so the total network bandwidth spent distributing each new version grew with the square of the number of hosts. The switch to TCP/IP on 1 January 1983 had made it easy to attach whole new networks, and organisations wanted to manage their own names without waiting for the NIC to update a master file.

The design: a tree, delegated

RFC 882 states the basic need as "a consistent name space which will be used for referring to resources", and argues that the size of the database and the frequency of updates mean it "must be maintained in a distributed manner, with local caching to improve performance". Its answer had three parts.

• A hierarchical name space. Names form a tree, read from the leaf toward the root. Any node can be handed to a different organisation to administer, so authority over a subtree can be delegated.
• Name servers. Server programs hold information about part of the tree and answer queries about it.
• Resolvers. Programs on the user's side that extract information from name servers in response to user requests, caching answers locally.

The system was also designed to be general, not just a host-address table. RFC 881, Postel's companion plan, notes that the domain server design could also map mailbox addresses to the host name of the mail server for that mailbox, so that a mailbox could belong to an organisation rather than to a particular machine.

The roll-out and the top-level domains

RFC 881 was frank about the catch: domain-style names required a great deal of software to change, and some groups wanted to use them at once while others did not want to see them for a long time. Its solution was a schedule. Initially every host would sit in a single domain, "ARPA", with a second domain, "DDN", for the defence network to follow; other domains could be added if they met stated requirements.

The list of top-level domains that people now recognise was set out in RFC 920, by Postel and Reynolds, in October 1984: ARPA for the existing ARPA-Internet hosts, then GOV, EDU, COM, MIL and ORG, plus two-letter country codes. NET does not appear in RFC 920; it was introduced in January 1985. So .com is not as old as DNS itself — it is about a year younger.

From 882 and 883 to 1034 and 1035

The 1983 documents were explicitly a starting point. In January 1986 Mockapetris published RFC 973, collecting changes and lessons from the first implementations. In November 1987 he replaced the whole set with RFC 1034 (concepts) and RFC 1035 (implementation), which declare RFCs 882, 883 and 973 obsolete. RFC 1034 describes the history in its own words: the distributed design had been described in RFCs 882 and 883 and, "based on experience with several implementations", evolved into the 1987 scheme. Later extensions — DNSSEC signatures, DNS over HTTPS — sit on top of that 1987 base.

Who invented DNS

The Internet Society's Brief History of the Internet says plainly that DNS "was invented by Paul Mockapetris of USC/ISI". The Internet Hall of Fame, which inducted him in 2012, likewise credits him with inventing it in 1983, after he recognised the problem of keeping every name-to-address translation in a single table on a single host. The surrounding work was collective: Postel, also at ISI, wrote the roll-out plan and co-wrote the top-level domain list, and the NIC at SRI, led by Elizabeth Feinler, had run the host table that DNS replaced.

For what DNS does today, see DNS in the glossary; its neighbours in time are on the Internet and Web timeline, from the ARPANET to the World Wide Web proposal that would soon put domain names in front of everyone.