DNS performs a crucial role in enabling user access to network resources so that users need not remember IP addresses and individual computers need not store a huge volume of domain names mapped to IP addresses. DNS employs a client/server model; a DNS server resolves a query for a DNS client by looking up the domain in its cache and if necessary sending queries to other servers until it can respond to the client with the corresponding IP address.
The DNS structure of domain names is hierarchical: the
top-level domain (TLD)
in a domain name can be a generic TLD (gTLD): com, edu, gov, int, mil, net, or org (gov and mil are for the United States only) or a country code (ccTLD), such as au (Australia) or us (United States). ccTLDs are generally reserved for countries and dependent territories; they are sometimes used in an unrelated context.