The Domain Name System (DNS) acts as the Internet’s address book, translating human-friendly domain names into IP addresses that computers use to communicate. Without DNS, accessing websites and online services would be complex and error-prone. This article explains how DNS works, its core components like zones and records, different types of queries, and the importance of configurations like Split DNS in modern networks.

How DNS Works?

When you type a domain name like example.com into your web browser, your device doesn’t know the IP address right away. It first sends a DNS query to a local DNS resolver — usually operated by your internet service provider (ISP) or your network’s own DNS server. This is called the initial query.
The resolver checks if it already has the answer cached. If not, it starts contacting other DNS servers to find the correct IP address for the domain you requested.

2. Local Cache Check:

Before reaching out to external servers, the DNS resolver first checks its local cache — a temporary storage of recently looked-up domain names and their corresponding IP addresses.
If the requested domain is already stored and the information is still valid (not expired), the resolver immediately returns the cached IP address to the client.
This cache check speeds up the process significantly, reducing internet traffic and improving the user’s browsing experience.

3. Recursive Resolution:

If the DNS resolver doesn’t find an answer in its cache, it acts on behalf of the client, querying a series of external servers step-by-step — starting from root servers, then TLD servers, and finally the authoritative server — until it retrieves the correct IP address for the domain.

Root Servers

A root server is the first major stop when looking up a website’s IP address through the Domain Name System (DNS). Think of it like a giant directory that helps computers find the next step. It doesn’t store the exact address you’re asking for but tells your computer which top-level domain (TLD) server — like .com, .net, or .org — you should ask next.

There are only a few hundred root servers worldwide, but they are critical because they keep the entire internet organized and help every DNS query find its way faster.

TLD Servers (Top-Level Domain Servers)

TLD servers are special DNS servers that manage the last part of a domain name — like .com, .net, .org, or country codes like .uk or .jp.

When your computer contacts a root server and asks for a website, the root server points it to a TLD server based on the domain extension. The TLD server then directs your computer to the correct authoritative server that knows the exact IP address of the website you want to visit.

Authoritative Server

An authoritative server is the final source of truth in the DNS process. It holds the actual records (like IP addresses) for domain names. When a DNS query reaches an authoritative server, it provides the exact IP address needed to access the requested website. Unlike other servers, it doesn’t ask anyone else for the answer—it already knows it.

For example, if you request information about Hastyread, the authoritative server for that domain responds with the correct IP address, allowing your browser to quickly load the site.

Response to Client

Once the DNS resolver finds the correct IP address by communicating with other servers, it sends that IP address back to your computer (the client). This allows your browser to connect directly to the website you asked for. It’s like getting the exact location you need after asking for directions — now you can go straight there!

Note: The entire process is typically completed in milliseconds due to DNS efficiency and caching mechanisms.

DNS Resolution Process

Authoritative DNS servers store and provide the official IP addresses for domain names. They directly answer queries about a domain. Recursive DNS servers, meanwhile, act like intermediaries. They search across multiple DNS servers to find the correct IP address for a user’s request, ensuring fast, smooth internet browsing.

Authoritative DNS Server

Imagine an authoritative DNS server like an official contact list that stores the true connection between website names and their IP addresses. When asked about a domain, it provides the exact IP without needing to look elsewhere. It is the final authority for the domains it manages, ensuring users get directed to the correct destination.

Recursive DNS Server

The recursive DNS server acts like a smart messenger. When you enter a website name, it first checks its memory. If it doesn’t know the answer, it quickly searches across the internet’s directory system, gathers the correct IP address, and brings it back to your device so the website can open.

Domain Name System (DNS): Zones

A DNS zone represents a portion of the domain namespace managed by a specific organization or administrator. It contains a collection of resource records that define mappings between domain names and IP addresses.

Types of DNS Zones:

• Forward Lookup Zone:
  Resolves FQDNs (fully qualified domain names) to IP addresses.
  Example: www.example.com → 192.0.2.1
• Reverse Lookup Zone:
  Resolves IP addresses to domain names using PTR records.
  Example: 192.0.2.1 → www.example.com

Core DNS Record Types

DNS Query Types

DNS Split

DNS split, also known as split-horizon DNS, is a method where two different DNS responses are given based on where the user is connecting from — inside or outside a private network. It allows different DNS responses based on the querying source. For example, if someone inside a company’s network asks for a website address, they might get a private internal IP. But if someone from outside asks, they receive the public IP. This technique improves security by hiding internal infrastructure and helps manage traffic better between internal and external users. It’s commonly used in businesses to protect sensitive resources and optimize network management.

• Internal Clients: Receive private IP addresses for corporate resources.
• External Clients: Receive public IP addresses for services exposed to the internet.

Use Case Example:

• Internal crm.company.local → 10.0.0.5
• External crm.company.com → 203.0.113.5

This approach improves security, prevents DNS leakage, and optimizes access control.

DNS Zone Types

Best Practices for DNS Deployment

• Use Redundant DNS Servers: Deploy at least two authoritative DNS servers in different geographic locations.
• Enable DNSSEC: Use DNS Security Extensions to protect against spoofing and ensure data integrity.
• Minimize TTLs Carefully: Short TTLs allow faster propagation of changes but increase server load.
• Segment Internal and External DNS: Apply split DNS architecture to safeguard internal networks.
• Regularly Update Root Hints and Zone Transfers: Ensure reliable forwarding paths and replication accuracy.

What is DNS spoofing?

DNS spoofing, also called DNS cache poisoning, is a cyberattack where fake or malicious data is inserted into the cache of a DNS resolver. When a user tries to access a website, instead of reaching the legitimate site, they are unknowingly redirected to a fraudulent one controlled by the attacker. This fake website may look identical to the real one and is often used to steal sensitive information like usernames, passwords, or financial details.

The attack typically works by exploiting vulnerabilities in the DNS system or tricking the resolver into accepting false information. Once the resolver’s cache is poisoned with the wrong IP address, it continues sending future visitors to the fake site until the cache is cleared.

DNS spoofing can have serious consequences. It can lead to identity theft, malware infections, or large-scale data breaches. To protect against it, organizations and individuals use security measures like DNSSEC (Domain Name System Security Extensions), which helps ensure that the DNS data has not been tampered with. Regularly clearing DNS caches and using secure, trusted DNS servers are also good preventive steps.

In short, DNS spoofing undermines the trust users place in web addresses by manipulating the system that translates domain names into IP addresses.

Important Notes for Certification

• DNS uses UDP port 53 by default (TCP is used for zone transfers and large queries).
• Root hints are critical for bootstrapping recursive queries.
• Zone transfers (AXFR, IXFR) are often secured via IP whitelisting or TSIG keys.
• Public DNS Examples: Google (8.8.8.8), Cloudflare (1.1.1.1).