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    Networking 5 min read

    The internet is a global network of computers that communicate with one another via TCP/IP protocol. Connected devices, including websites, communicate using their unique IP address, which is a long string of numbers.

    But long strings of digits are hard for humans to remember, so websites use a word based format – or domain name – as well. Thus, every site will have both a domain name and a corresponding IP address.

    Domain name system is like a phonebook for the internet. It keeps track of the URL for each website, and its corresponding IP address.

    DNS Definition

    Short for Domain Name System, DNS is an Internet service that translates domain names to IP addresses.

    Think of google.com, youtube.com or skynews.com – all of these contain words or phrases that make it obvious what the site is about. This serves the site, by allowing it to announce its “brand” or purpose, and it serves the user because it’s easy to remember.

    But the internet is based on numeric IP addresses; devices cannot read domain names. Therefore, a domain name system server is required to “translate” the URL into its underlying IP address, which can be read by connected devices.

    For example, the domain www.example.com might resolve (translate) to 198.105.232.4.

    The domain name system is, in fact, its own network in which different types of server handle different segments of information. When a query enters the system, the DNS root server (the entry point) directs the query down the hierarchy of servers until the data is located.

    What is a DNS server?

    A DNS server is a database containing the IP addresses that correspond with domain names, or URLs. It functions as a phonebook for the internet. Each time a user navigates to a website using its domain name, DNS locates the corresponding IP address, which can be “read” by the servers of that website. With your request translated into the correct syntax, the website’s servers can understand the request and serve up the page.

    How does DNS work?

    The process of translating a URL based query into a readable IP based request takes place in four stages. Each stage is carried out by its own dedicated server in the Domain Name System.

    1) DNS Recursor (or DNS resolver)

    This is the first recipient of your query. This is effectively your internet service provider, which starts by checking its own cache memory for the domain you’ve entered. If it’s unable to locate this information in its cache, it will send your query to the next level of DNS servers, known as root servers.

    2) Root Servers

    Root servers sit at the top of the domain name system system hierarchy. There are 13 root servers in existence, positioned strategically around the world and operated by a group of organizations. When a Root Server receives your query, it will pass it down to the next level of servers in the DNS hierarchy, known as Top Level Domain servers.

    3) TLD Servers

    Top level domain servers store all of the address information for top level domains, for example .com or .org. Although the TLD cannot point directly to the IP address you’re looking for, it will be able to direct you to the final level of servers, which can provide the specifics.

    4) Authoritative Name Servers

    These are the final level of DNS servers. These are the final authority, responsible for knowing everything about a domain including its IP address. When an authoritative name server receives your query from the resolver, it will respond with the IP address you’re looking for. With the data sent back to your computer, you’ll now be able to access that web page.

    Authoritative DNS servers v recursive DNS servers

    Recursive DNS server

    A recursive DNS server is the first place your query goes when you type in a domain name. It functions as a middleman between you, the end user, and the authoritative name server, which provides the IP address you’re seeking.

    Recursive servers, or resolvers, are commonly provided by internet service providers. Sometimes, the recursive server will be able to locate the domain name you’ve entered in its cache, from a previous search. Where this is not the case, it will pass your query on to the DNS servers to be located.

    Authoritative DNS server

    The authoritative DNS server is the final point of call for any DNS query. This server holds all information for a given domain name, including its IP address. Once this information is transmitted back to the resolver, and finally your browser, you’ll be able to acess the page you’ve requested.

    DNS servers and IP address

    How are DNS and IP addresses related? Simply put, if there were no domain name system, you would need to memorize the IP address for every website you wanted to visit.

    For example, instead of typing webopedia.com into your browser, you’d need to remember 172.66.40.224. It doesn’t have quite the same ring to it.

    Imagine having to do this for every website. DNS therefore performs an essential role in making the internet accessible and intuitive for humans, while conforming to the underlying TCP/IP protocol.