Additional Lessons
Lesson 4

DNS Overview

By Sai Kurada
August 22, 2023

DNS Overview

The Domain Name System (DNS) is a fundamental protocol used on the Internet and most private networks. It serves as the "phone book" of the internet, translating human-readable domain names (like into IP addresses (like, which computers use to identify each other on the network. DNS plays a crucial role in enabling the easy and user-friendly access to websites and services by mapping domain names to their corresponding IP addresses.

Here's an overview of how DNS works:

  1. Domain Name Hierarchy: The DNS system is organized hierarchically. At the top of the hierarchy are the root servers, which are responsible for directing queries to the appropriate top-level domains (TLDs) such as .com, .org, .net, etc.
  2. DNS Query: When a user enters a domain name into a web browser or other application, the system generates a DNS query to resolve the domain name to an IP address. The query is sent to a DNS resolver, which could be provided by the user's ISP, a public DNS service like Google DNS or Cloudflare DNS, or an organization's internal DNS server.
  3. Caching: DNS resolvers often cache responses to queries to speed up future queries for the same domain. This helps reduce the overall DNS query load and improve performance.
  4. Recursive Query: If the resolver doesn't have the IP address for the requested domain in its cache, it performs a recursive query. In a recursive query, the resolver starts from the root DNS servers and follows the hierarchy down to the authoritative DNS servers for the specific domain.
  5. Authoritative DNS Servers: The authoritative DNS servers are responsible for storing the DNS records for a particular domain. These records include information like the IP addresses associated with the domain, mail server addresses, and more. There are different types of DNS records, such as A records (for IPv4 addresses), AAAA records (for IPv6 addresses), MX records (for mail servers), and others.
  6. DNS Resolution: The recursive resolver receives responses from authoritative servers and stitches together the information to form a complete response. It then stores this information in its cache for future use and returns the IP address to the application that initiated the DNS query.
  7. TTL (Time-to-Live): Each DNS record has a TTL value that specifies how long the information can be cached by resolvers before it needs to be refreshed from the authoritative servers. This helps ensure that changes to DNS records are propagated efficiently.

Benefits of DNS:

  1. Human-Readable Addresses: DNS makes it easy for users to access websites and services using human-readable domain names, rather than having to remember numeric IP addresses.
  2. Load Distribution: DNS can be used to distribute traffic across multiple servers by using techniques like round-robin DNS.
  3. Redundancy: Multiple IP addresses can be associated with a single domain, providing redundancy and failover capabilities.
  4. Centralized Management: DNS allows centralized management of domain name assignments and changes, making it easier to update information as needed.
  5. Fast Resolving: Cached DNS responses allow for quicker access to frequently visited sites, reducing the time it takes to establish connections.

In summary, DNS is a critical component of the modern internet infrastructure that enables users to access websites and services using human-friendly domain names, translating them into the IP addresses required for network communication.