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Document INF/6-E

14 October 2002

Original: English





Note by the Secretary General


Information paper

Internet Domain Name System Basics


To understand the issues related to Internet domain names, it helps to start with Internet Protocol (IP) addresses.  This is a number that identifies each computer (or application) connected to the Internet.

One might think that this is no different from a telephone number, but this is not quite right.  A telephone number (or at least a fixed-line telephone number) identifies the wire, the line, coming out of a central switch and going to a home or office.  It does not identify the terminal device (the telephone) itself.  There are other important differences between telephone numbers and IP addresses, for more details, please see the paper at: .

But for the purposes of this very summary introduction, all we need to know is that each computer on the Internet is identified by an IP address.  IP addresses are currently 32 bits long.  As the Internet has grown, the number of devices that need IP addresses has grown, leading to the development of a longer form of IP address, the IP address Version 6 (IPv6).  A discussion of the issues related to the transition from current IP addresses to IPv6 is given in the paper referenced above.

But how do we get from IP addresses to domain names?  The Internet was initially implemented as a research and military network.  As its popularity grew, users and administrators found that it was inconvenient to have to remember the IP address (a number) of specific computers or applications, so a system to map user-friendly names to IP addresses was developed.

There are many ways to build such systems.  The method chosen was the well-known hierarchical design.  That is, a hierarchical name space was created.  At the top level, some of the names chosen were "edu" for computers in US universities, "mil" for computers in the US military, "com" for computers in commercial companies, and "int" for international organizations (there are several other so-called generic top-level domain names-gTLDs).  Computers outside the US were under top level codes derived from the ISO list of country codes, for example "fr" for France (these codes are called ccTLDs).  The registration of names under ccTLD codes is typically (but not always) handled by an organization located in the country corresponding to ccTLD code.  This system of mapping names to IP addresses is called the Domain Name System (DNS).  It is comprised of many individual computer systems.  For more details on the DNS, please see the paper at: .

Any number of names can be created under each name at the top level.  The levels are separated by a period (full stop).  For example, there is an entry "itu" under "int".  Any number of names can be created under second-level names.  For example, identifies a computer that is the external web server of the ITU.

Whenever a user types the name (called a domain name), software looks up the name in the hierarchical domain name system and returns the IP address of the external web server of the ITU, allowing users to access the web pages on that computer.  For more details of how the domain name system is actually structured and on how it functions, please see the presentation at: .

There were no real issues with this hierarchical system so long as the Internet was mostly used for research.  But its growing popularity and wide implementation led to calls to remove the restrictions on commercial use that had originally been imposed by the US agencies that had sponsored the development of the network.  Once these restrictions were removed, there was very rapid growth in the names registered under the "com" gTLD.

More importantly, the names started to be used to refer to "real world" objects, rather than just to refer to computers.  For example, the expectation was that "" would refer to the web pages of the real-world ITU, and not just to the web pages of some organization that had chosen to register the domain name "itu", or to some computer that the ITU had chosen to name "www".  This expectation was particularly strong for commercial companies registering domain names in the "com" gTLD.  Trademark owners requested that measures be taken to ensure that their trademarks were not used as domain names by other companies.

In addition, the rapid growth in the demand for domain names led to calls for the introduction of competition in domain name registrations, which had previously been handled mostly by a single organization.

As a result of these pressures, as well as the recognition that the Internet was rapidly evolving into an important international infrastructure and that therefore it was appropriate to revisit the methods that had previously been used to ensure coordination and stable expansion of the domain name system, a series of consultations were initiated, which resulted in the creation of the coordination structure that is in place today.  This and some subsequent developments are described in the introduction to the proposed draft revision of Resolution 102 (DT 30)[1].



[1] See also Plenipotentiary Information Document 4 at



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