Design Domain Name System (DNS)

Let’s consider the example of a mobile phone where a unique number is associated with each user. To make calls to friends, we can initially try to memorize some of the phone numbers. However, as the number of contacts grows, we’ll have to use a phone book to keep track of all our contacts. This way, whenever we need to make a call, we’ll refer to the phone book and dial the number we need.

Similarly, computers are uniquely identified by IP addresses—for example, 104.18.2.119 is an IP address. We use IP addresses to visit a website hosted on a machine. Since humans cannot easily remember IP addresses to visit domain names (an example domain name being educative.io), we need a phone book-like repository that can maintain all mappings of domain names to IP addresses. In this chapter, we’ll see how DNS serves as the Internet’s phone book.

What is DNS?

The domain name system (DNS) is the Internet’s naming service that maps human-friendly domain names to machine-readable IP addresses. The service of DNS is transparent to users. When a user enters a domain name in the browser, the browser has to translate the domain name to IP address by asking the DNS infrastructure. Once the desired IP address is obtained, the user’s request is forwarded to the destination web server.

The slides below show the high-level flow of the working of DNS:

The entire operation is performed very quickly. Therefore, the end user experiences minimum delay. We’ll also see how browsers save some of the frequently used mappings for later use in the next section.

Important details

Let’s highlight some of the important details about DNS, some of which we’ll cover in the next section:

• Name servers: It’s important to understand that the DNS isn’t a single server. It’s a complete infrastructure with numerous servers. DNS servers that respond to users’ queries are called name servers.

• Resource records: The DNS database stores domain name to IP address mappings in the form of resource records (RR). ...