ITS is the Domain Name Registrar for the university and provides DNS hosting services for university-affiliated custom domain names.

What is a Domain Name?

Generally speaking, domain names are the familiar, easy-to-remember and always unique names of computers on the Internet. Domain names distinguish computers on a network. Remember, though, the real work of identifying and distinguishing computers on a network is done by the IP address. DNS simply translates domain names into the numeric IP address because humans find IP addresses hard to remember.

Technically speaking, a domain name is a hierarchical series of character strings representing different levels of domains separated by dots (periods) proceeding from top-level domains at the right end of the name to specific host names to the left. The individual words or characters between the dots are called labels. The label furthest right represents the top-level domain. The second label from the right represents the second-level domain. Any labels to the left of the second-level domain are considered subdomains of the second-level domain (sometimes called third-level domains). A fully qualified domain name (FQDN) is a domain name that extends all the way back to root. It must include the root "." at the end of the name to be considered a FQDN (e.g., "computerstore.utexas.edu." not "computerstore.utexas.edu").

At the university, ITS is owner (Domain Name Registrar) of the utexas.edu second-level domain and creates subdomains at the request of departments or organizations within the university as approved by the University Communications Standards Committee (UCSC).

Domains and Domain Hierarchy

In the Domain Name System (DNS) hierarchy, domains consist of the root-level domain at the top (administered by InterNIC), with top-level domains underneath, followed by second-level domains and finally subdomains.

Top-Level Domains

A top-level domain is the label at the right end of the domain name, after the dot. There are two types of top-level domains, generic and country code:

• Generic Top-Level Domains (TLDs or gTLDs): Created for use by the Internet public. These are: .aero, .biz, .com, .coop, .edu, .gov, .info, .int, .mil, .museum, .name, .net, and .org (.pro is being established).

• Country Code Top-level Domains (ccTLDs): Two letter domains which correspond to a country, territory or other geographic location (e.g., .uk, .de, .jp, .us).

Second-Level Domains

A domain is a second-level domain if it is contained within a top-level domain. A second-level domain is the label immediately to the left of the top-level domain, separated by a dot.

Subdomains

A domain is a subdomain of another domain if it is contained within that domain. A subdomain is the label immediately to the left of a second-level domain.

How Domain Names are Assigned

The Internet Corporation for Assigned Names and Numbers (ICANN) is the ultimate authority for domain-name assignments. ICANN conveys authority to (accredits) Registrars throughout the world to register second-level domains within specific top-level domains; this ensures that all domain names are unique.

The owner of a particular second-level domain then can create an unlimited number of domains (subdomains) that use the original name as a suffix. These subdomains sometimes represent different computer servers within different departments. Several examples of subdomains within the utexas.edu second-level domain are gslis.utexas.edu, computerstore.utexas.edu, po.utexas.edu,engr.utexas.edu.

Each subdomain can have its own subdomains. In the example below, each label represents a subdomain of the (sub)domain immediately to its right, separated by a dot; all these domains are within the second-level domain utexas.edu:

one.example.of.many.subdomains.in.the.domain.utexas.edu

There can be no more then 127 labels. No label can be longer than 63 characters.

Further Reading

• InterNIC FAQs: The Domain Name System: A Non-Technical Explanation — Why Universal Resolvability Is Important

• InterNIC FAQs on the Domain Names, Registrars, and Registration

• ICAAN Frequently Asked Questions (FAQs)

• RFC 1591 - Domain Name System Structure and Delegation

• RFC 1034 - Domain Names -- Concepts and Facilities

• RFC 921 - Domain Name System Implementation Schedule - Revised

• RFC 920 - Domain Requirements