The Domain Name System (DNS) is a fundamental
component of the modern Internet, providing a critical
link between human users and Internet routing infrastructure by mapping host names to IP addresses. The DNS utilizes a hierarchical name space divided into zones, or domains. This hierarchy is manifested in the widespread “dots” structure. For example, com is the parent zone for example.com, microsoft.com, cnn.com, and approximately 20 million other zones.
Each zone has one or more authoritative name servers.
These are dedicated servers, whose job is to answer queries for names within their zone(s). For example, UCSD has three authoritative name servers