The Domain Name System
The Domain Name System (DNS) is the naming system for all computers and servers connected to the internet. The DNS associates information with its corresponding domain name. You can think of the DNS as an address book for the internet, and of each domain name as a contact in the address book.
Domain Names
A domain name is just the address of a website. Examples of domain names include google.com, twitter.com, and medium.com. Although domain names are easy to remember for humans, computers prefer using numbers.
IP Addresses
Internet Protocol (IP) addresses are the addresses used by computers to identify other computers on the internet. Every computer connected to the internet is assigned a unique IP address by its router. To send information from one computer to another through the internet, the sender must know the receiving computer’s IP address.
How It Works
The primary function of the DNS is to associate domain names with IP addresses. This usually happens when you try to access a website using its domain name. If you computer does know know the IP address of the website you are trying to access, it uses the DNS to find the IP address by sending a lookup request to a DNS name server. The request includes the domain name you are looking up, and the response from the server includes the IP address associated with that domain. This entire lookup process typically takes less than a second. The DNS also specifies the DNS Protocol, a part of the Internet Protocol Suite that outlines how the data communications are carried out between computers at the network level.
Root Name Servers
This information is stored on DNS name servers, which serve as a database of every website on the internet. This database stores information about domain names like their A (AAAA) Records, Name Server (NS) Records, and Mail Exchanger (MX) Records. Each of these records contains different information about the domain. To access a website like www.google.com you need A Records, but to send an email to person@google.com you need MX Records. A complete list of record types can be found here.
There are thirteen root name servers that store this information. This does not mean that there are thirteen physical servers, but that the information is divided up into thirteen logical servers with physical servers located all around the world. Each operator uses redundant server backups in case of hardware or software failure. You can see a map of of these servers here.
Who Does All This
The DNS is maintained and administered by the Internet Corporation for Assigned Names and Numbers (ICANN). ICANN is based in Los Angeles, California, and is responsible for the DNS, IP address allocation, the protocol parameter registry, root server systems, generic top level DNS management, country code top level domain name DNS, and time zone database management.
