How DNS Works: A Comprehensive Guide

Let’s Understand How DNS Works and key types of DNS records

In this comprehensive guide, we delve into the intricacies of how DNS works, providing a detailed look at the role of the DNS server in the modern internet. From the basics of DNS to understanding the various types of DNS records, this article is your go-to resource for mastering the essentials of DNS and enhancing your website’s performance and security.

DNS (Domain Name System) is a fundamental technology that translates domain names into IP addresses, enabling browsers to locate and load websites. Here’s a detailed explanation of how DNS works with the help of various DNS records:

Key Types of DNS Records

1. A Record (Address Record):
   • Function: Maps a domain name to an IPv4 address.
   • Example: example.com has an A record pointing to 192.0.2.1.
2. AAAA Record (IPv6 Address Record):
   • Function: Maps a domain name to an IPv6 address.
   • Example: example.com has an AAAA record pointing to 2001:db8::1.
3. CNAME Record (Canonical Name Record):
   • Function: Maps an alias domain name to another domain name (canonical name).
   • Example: www.example.com is a CNAME for example.com.
4. MX Record (Mail Exchange Record):
   • Function: Specifies the mail servers responsible for receiving email for a domain.
   • Example: example.com has an MX record pointing to mail.example.com.
5. TXT Record (Text Record):
   • Function: Allows domain administrators to insert arbitrary text into DNS records. used frequently for security and verification reasons.
   • Example: A TXT record can be used to verify domain ownership or include SPF (Sender Policy Framework) data for email security.
6. NS Record (Name Server Record):
   • Function: Indicates which DNS servers are authoritative for a particular domain.
   • Example: example.com has NS records pointing to ns1.example.com and ns2.example.com.
7. SRV Record (Service Record):
   • Function: Specifies the location of specific services within a domain.
   • Example: Used to locate services like SIP servers or LDAP servers.
8. PTR Record (Pointer Record):
   • Function: Maps an IP address to a domain name (reverse DNS lookup).
   • Example: 192.0.2.1 has a PTR record pointing to example.com.

DNS Resolution Process

1. User Query: A user types a domain name (e.g., www.example.com) into their web browser.
2. Local Cache Check: The user’s device checks its local DNS cache for the IP address of the domain.
3. Recursive DNS Server Query: If the IP address is not in the local cache, the device queries a recursive DNS server (provided by the ISP or a third-party service).
4. Querying the DNS Hierarchy:
   • Root Servers: The recursive DNS server queries a root DNS server for information about the domain.
   • TLD Servers**: The root server directs the query to the appropriate Top-Level Domain (TLD) server (e.g., for .com).
   • Authoritative Servers: The TLD server directs the query to the authoritative DNS server for the specific domain (e.g., example.com).
5. Authoritative DNS Server Response: The authoritative DNS server provides the necessary DNS records, such as the A record containing the IP address.
6. Returning the IP Address: The recursive DNS server returns the IP address to the user’s device.
7. Connecting to the Web Server: The user’s device uses the IP address to connect to the web server and load the website.

Example Scenario

1. The user enters www.example.com in their browser.
2. The device checks the local DNS cache for an A record for www.example.com.
3. If not found, the device queries the recursive DNS server.
4. The recursive server queries the root server, which points to the .com TLD server.
5. The TLD server directs the query to the authoritative DNS server for example.com.
6. The authoritative server responds with the A record (192.0.2.1) for www.example.com.
7. The recursive server returns the IP address to the user’s device.
8. The browser connects to 192.0.2.1 and loads the website.

Additional Record Usage

• CNAME Records: If www.example.com is a CNAME for example.com, the query resolves to example.com, and then the A record for example.com is used.
• MX Records**: When sending an email to user@example.com, the mail server queries the MX records for example.com to find the mail server to handle the email.
• TXT Records: Used for domain verification or to include SPF information to prevent email spoofing.
• NS Records: Direct the query to the correct authoritative servers for the domain.
• SRV Records: Used to locate specific services within the domain.

DNS records ensure the correct translation of domain names into IP addresses and provide essential information for various internet services, enabling seamless connectivity and communication across the internet.

Also Read: What steps do I follow to set up domain and DNS settings for my Linux VPS?

-Written By Vishwanath