Additional Lessons
Lesson 4

DNS Components

By Sai Kurada
August 23, 2023

DNS Components

The Domain Name System (DNS) consists of several key components that work together to enable the translation of human-readable domain names into IP addresses. These components ensure the efficient and accurate resolution of DNS queries.

Here are the main components of DNS:

DNS Client: This is the software component running on a user's device or application that initiates DNS queries. The DNS client sends queries to DNS resolvers to obtain the IP address corresponding to a given domain name.

DNS Resolver: The resolver is responsible for receiving DNS queries from clients and finding the corresponding IP address. There are different types of resolvers:
  • Stub Resolver: This is a simplified resolver present on client devices. It sends queries to recursive resolvers to resolve domain names.
  • Recursive Resolver: The recursive resolver performs the actual work of finding the IP address for a domain name. It may query multiple DNS servers in a hierarchical manner to resolve the domain. Recursive resolvers also maintain caches to store DNS responses for faster future lookups.

Root DNS Servers: These are the highest-level DNS servers in the hierarchical DNS structure. There are a relatively small number of root servers worldwide. They provide information about the authoritative DNS servers for top-level domains (TLDs) like .com, .org, and country-code TLDs like .uk, .jp, etc.

Top-Level Domain (TLD) DNS Servers: These servers are responsible for managing the DNS records for specific top-level domains (e.g., .com, .org, .net). They provide information about the authoritative DNS servers for second-level domains within their TLD.

Authoritative DNS Servers: These servers are the ultimate source of truth for DNS records for specific domain names. They store the DNS records that map domain names to IP addresses. There are different types of authoritative DNS servers:
  • Primary (Master) Server: This server holds the original copy of DNS records for a domain. Changes are made here first.
  • Secondary (Slave) Server: These servers obtain DNS records from the primary server and provide redundancy. They periodically synchronize with the primary server to ensure consistency.
  • Caching Only Server: These servers do not store authoritative records but only maintain caches of DNS responses. They can quickly respond to queries for previously resolved domain names.

DNS Records: DNS records are data entries stored on authoritative DNS servers. They contain information that maps domain names to IP addresses and serve various purposes. Common DNS record types include A, AAAA, MX, CNAME, TXT, NS etc.

DNS Zone: A DNS zone is a portion of the DNS namespace managed by a specific organization or entity. It contains authoritative DNS records for a domain and its subdomains.

TTL (Time-to-Live): TTL is a value associated with DNS records that determines how long resolvers can cache the record's information before requesting an update from authoritative servers.

These components work together to ensure that DNS queries are efficiently resolved, allowing users to access websites and services using human-readable domain names. The distributed and hierarchical nature of DNS helps ensure reliability and scalability across the global network.