Domain Name System (DNS)

What is DNS?

The Domain Name System (DNS) is the address book of the Internet. Domain names are used by people to access information online. Through Internet Protocol (IP) addresses, web browsers can communicate. In order for browsers to load Internet resources, DNS converts domain names to IP addresses.

Each Internet-connected device has a distinct IP address that other computers can use to find the device. DNS servers replace the need for people to memorize IP addresses or more complicated modern alphanumeric IP addresses.

How does DNS work?

Your computer searches for the corresponding IP address of a website when you enter its address into a search engine to find the correct page.

The hostname-to-IP address translation, commonly known as DNS resolution, involves four primary servers. This includes the recursive DNS server, the root name server, the top-level domain (TLD) nameserver, and the authoritative nameserver.

Your browser receives the data after the correct IP address has been identified and the web page loads. Additionally, the recursive DNS server keeps that IP in its cache memory for a short while. This is done so that the server won't need to ping other servers in order to quickly return the address.

An error notice is shown to your browser if a query reaches the authoritative name server level and the IP address is still unreachable. Although it may seem like a long process, it usually just takes a few milliseconds.

What are the steps in a DNS lookup?

There are eight simple steps in a DNS lookup:

1. When a user enters "example.com" into a web browser, the query is sent over the Internet and is retrieved by a DNS recursive resolver.
2. The resolver then queries a DNS root nameserver.
3. After that, the root server responds to the resolver with the address of a Top Level Domain (TLD) DNS server (like.com or.net), which stores the data for its domains. When searching for example.com, the request is pointed toward the .com TLD.
4. The resolver then requests the .com TLD.
5. The TLD server then responds with example.com's nameserver's IP address.
6. The recursive resolver then sends a query to the nameserver for the domain.
7. The nameserver then provides the resolver with the IP address for example.com.
8. The IP address of the domain that was originally requested is then returned by the DNS resolver to the web browser.

 What are the types of DNS queries?

Three different types of queries are used in normal DNS lookups. An optimised DNS resolution process can reduce the distance traveled by using a combination of these queries. In a perfect world, a DNS name server would be able to respond to a non-recursive query thanks to cached record data.

The three types of queries are:

1. Recursive query

   A DNS client requires a DNS server to respond to a recursive query with either the requested resource record or an error message in the event that the resolver cannot locate it.

2. Iterative query
   In this case, a DNS client will allow a DNS server to provide the best response it can. A referral to a DNS server authoritative for a lower level of the domain namespace will be returned if the queried DNS server does not have a match for the query name. 

3.  

   Non-recursive query
   This usually happens when a DNS resolver client asks a DNS server for a record that the server already has access to, either because the server is authoritative for the record or because the record is already in the server's cache. Typically, a DNS server will cache DNS records to reduce upstream servers' load and additional bandwidth usage.