How DNS Ad Blocking Works: A Beginner's Guide

When I first heard about DNS ad blocking, I thought it sounded complicated. Turns out, it's actually pretty simple once you understand the basics. Let me break it down for you.

What is DNS?

Before we talk about blocking ads, let's understand what DNS is. Don't worry - I'll keep it simple!

DNS stands for Domain Name System. Think of it as the internet's phone book.

When you type "google.com" into your browser, your phone doesn't actually know where that is. It needs to look up the "phone number" (IP address) for Google's servers. That's where DNS comes in.

Here's what happens:

You type a website address
Your phone asks a DNS server: "Where is this website?"
The DNS server responds with the IP address
Your phone connects to that address

This happens in milliseconds, thousands of times a day, without you even noticing.

How Regular DNS Works

Normally, your phone uses whatever DNS server your internet provider gives you. This server just does its job - looking up addresses and returning results. It doesn't care if you're requesting a news article or an ad server.

The Magic of Ad-Blocking DNS

Here's where it gets interesting. An ad-blocking DNS server works the same way, but with one key difference: it maintains a blocklist.

When you request a website, the ad-blocking DNS checks:

Is this a legitimate website? ✅ Here's the address!
Is this an ad server? ❌ Sorry, doesn't exist!

By returning a "doesn't exist" response for known ad servers, the ads simply never load. Your phone tried to get them, but the DNS said "nope!"

Why This Method is So Effective

There are several reasons I love DNS-based ad blocking:

1. System-Wide Protection

Unlike browser extensions that only work in one app, DNS blocking works everywhere. Every app on your phone uses DNS, so every app gets ad blocking.

2. No Apps Required

You don't need to install any apps or give any special permissions. You're just changing which DNS server your phone talks to - a setting that's built right into iOS and Android.

3. Lightweight

Since the blocking happens at the DNS level, there's no heavy processing on your phone. No battery drain, no memory usage, no performance impact.

4. Hard to Bypass

Most ad blockers that work in browsers can be detected and bypassed. DNS blocking is much harder for advertisers to get around because it happens before your phone even connects to their servers.

What Gets Blocked?

A good ad-blocking DNS service typically blocks:

Ad networks (Google Ads, Facebook Ads, etc.)
Tracking domains (analytics, user tracking)
Malware domains (known malicious sites)
Telemetry (data collection from apps)

The blocklists are constantly updated as new ad domains appear.

What Doesn't Get Blocked?

It's important to understand the limitations:

First-party ads - If a website serves ads from its own domain, DNS blocking can't distinguish them from regular content
YouTube ads - These come from the same servers as the videos themselves
Sponsored content - Native ads that are part of the actual content

That said, DNS blocking still catches the vast majority of ads and trackers.

The Technical Stuff (Optional Reading)

If you're curious about the technical details, here's what's actually happening:

DNS Query Types

When your phone looks up a domain, it sends a DNS query. The ad-blocking DNS server intercepts this query and checks it against its blocklist.

For blocked domains, it returns one of these responses:

NXDOMAIN - "This domain doesn't exist"
0.0.0.0 - A null IP address
127.0.0.1 - Localhost (your own device)

Any of these responses effectively prevents the connection.

Encrypted DNS (DoH/DoT)

Modern DNS blocking uses encrypted connections:

DoH (DNS over HTTPS) - DNS queries encrypted like regular web traffic
DoT (DNS over TLS) - DNS queries encrypted with TLS

This means your internet provider can't see or interfere with your DNS queries. Extra privacy!

How to Set It Up

Ready to try DNS ad blocking? The setup is surprisingly simple:

On iOS:

iOS uses configuration profiles to set up encrypted DNS. You download a small file that tells your iPhone which DNS server to use. That's it!

View iOS Setup Guide →

On Android:

Android 9 and later has a "Private DNS" feature built right into the settings. You just enter the hostname of an ad-blocking DNS server.

View Android Setup Guide →

Choosing a DNS Provider

There are several good options for ad-blocking DNS:

NextDNS - Highly customizable, great blocklists
AdGuard DNS - Simple and effective
Quad9 - Focus on security
Cloudflare (1.1.1.1) - Fast, but doesn't block ads by default

I personally recommend NextDNS for most users because it gives you control over what gets blocked without being too complicated.

Frequently Asked Questions

Will this slow down my internet?

Nope! Good DNS servers are actually faster than your ISP's default servers. Plus, not loading ads means pages load faster overall.

Is it safe?

Absolutely. You're using the same technology that powers the internet - just with a smarter server. Encrypted DNS actually improves your security.

Can I undo it?

Yes! Just remove the DNS settings and you're back to normal. It's completely reversible.

Wrapping Up

DNS ad blocking is one of those rare solutions that's both simple and effective. You change one setting, and suddenly your entire phone is protected from ads and trackers.

No apps to install. No batteries to drain. No subscriptions required.

If you've made it this far, you now understand more about DNS than most people ever will. Time to put that knowledge to use!

Get Started with Setup →