Why DNS Blocking Cannot Stop YouTube Ads

The question everyone asks

Anyone who sets up DNS ad blocking soon asks the same question: why do YouTube ads still play? Banner ads on news sites disappear, smart TVs go quiet, but the pre-roll ad before a video still appears. It is not a configuration mistake. It is a fundamental limit of how DNS filtering works, combined with how YouTube delivers its ads.

Understanding the reason helps you set realistic expectations, avoid breaking YouTube by blocking the wrong domains, and decide which tools can help instead.

How DNS ad blocking works

DNS ad blocking works by refusing to resolve domains that serve advertising. When a web page tries to load an advert from a separate advertising domain, the DNS filter answers that lookup with 0.0.0.0 or NXDOMAIN. The advert fails to load, and the rest of the page continues normally. This works well whenever adverts are served from domains that are separate from the content you actually want.

The key assumption is separation. DNS sees only domain names. If the advert and the content come from the same domain, DNS cannot tell them apart.

How YouTube serves ads

YouTube delivers videos and video ads through the same infrastructure. Both are streamed from Google's video delivery domains, and the ad is typically stitched into the playback process by the player itself. From a DNS point of view, the lookup that fetches the ad looks the same as the lookup that fetches the video. Blocking the domain would block the videos as well. [VERIFY: describe current YouTube ad delivery only in general terms; avoid naming specific internal domains]

This is a deliberate design that many large platforms use, partly because it makes ad blocking harder and partly because it is simply efficient to deliver all video through one optimised network.

What happens if you try anyway

Lists circulate online that claim to block YouTube ads with DNS. In practice, they tend to do one of three things: block nothing useful, block a few tracking or ad-measurement domains without removing the ads themselves, or break YouTube playback entirely. Some cause videos to buffer endlessly or fail on certain devices. Because the platform changes regularly, even a list that seems to help one week may stop working the next.

If you have added such entries and YouTube misbehaves, check your query log for blocked lookups while playing a video and remove those entries from your blocklist.

The same applies to other platforms

YouTube is the best-known example, but the same limitation applies to many large services that serve ads from their own domains: social network feeds, some streaming services and some apps. Sponsored posts on social media are part of the feed itself. Ads inside streaming apps on smart TVs are often delivered with the stream. DNS filtering can reduce tracking around these services but rarely removes the ads.

• Ads served from the same domain as the content cannot be blocked by DNS
• Sponsored posts in social feeds are part of the content
• In-stream ads on TV apps usually share the video delivery domains
• Ad measurement and tracking domains can sometimes be blocked separately

What does help with YouTube ads

Removing ads that share a domain with the content requires a tool that can see inside the page or app, not just the domain name. Browser extensions that block ads work at that level: they can recognise and remove the ad elements and requests within the page. Their effectiveness varies as platforms change, and some platforms actively restrict them. The other option is a paid ad-free subscription offered by the platform itself, which is the only method that works reliably across devices and apps.

On smart TVs and mobile apps, browser extensions are not available, so in practice the choice is between accepting the ads and paying for an ad-free tier.

What DNS ad blocking is still good for

None of this makes DNS ad blocking pointless. On a typical home or office network, it removes a large share of banner advertising, pop-up ad networks and third-party trackers across every device, including devices where you cannot install anything. It reduces smart TV telemetry, cuts background requests and lowers exposure to malicious advertising, which is a real security risk. It just does not reach ads served from first-party domains.

• Removes many display ads on websites and in apps
• Reduces telemetry from smart TVs and IoT devices
• Blocks many third-party trackers
• Reduces exposure to malvertising

Combining tools sensibly

A practical setup combines layers. Use DNS filtering on the router to block malware, phishing, trackers and many ads for every device. Use a reputable ad-blocking extension in desktop browsers for the remaining in-page ads. For video platforms where ads bother you most, consider whether the ad-free subscription is worth it. This combination covers far more than any single tool, with little effort.

Being honest about expectations

We would rather explain this clearly than promise something DNS cannot deliver. FirewallDNS focuses on security filtering first: malware, phishing and newly registered domains, plus content categories and custom lists. Ad and tracker reduction is a useful side benefit on many devices. [VERIFY: whether ad and tracker blocking is a separate switch in the FirewallDNS dashboard] YouTube ads are outside what any DNS service can reliably block.

A short technical explanation

When you press play, the video player asks the platform's servers what to play. The answer can include both the advertisement and the video, delivered from the same pool of servers under the same domain names. The DNS lookups made by your device look identical whether the bytes that follow will be an ad or a video. A DNS resolver only sees the name being looked up, never the content that is downloaded afterwards, so it has nothing to distinguish one from the other.

Some platforms go further and insert the advert into the video stream on the server side before it is sent. In that case, even tools that inspect requests inside the browser struggle, because the ad and the video arrive as one continuous stream.

What about smart TVs and streaming boxes?

On smart TVs, DNS filtering still has a visible effect: home-screen advertising, automatic content recognition and telemetry often use separate domains and can be reduced. But ads inside the YouTube app, or inside other streaming apps, behave exactly as they do in a browser. Because there are no extensions on TVs, the realistic options are to accept the ads or subscribe to an ad-free tier. Blocking video delivery domains on a TV usually makes the app unusable.

If you want to see what your TV is doing, open your query log while the TV is on. You will typically see the platform domains used for video alongside separate telemetry and advertising domains. The separate ones are candidates for blocking; the video domains are not.

Common myths

A few myths keep circulating about DNS and video ads.

• Myth: a big enough blocklist will remove YouTube ads. Reality: size does not help when ads share domains with videos.
• Myth: blocking one specific subdomain removes ads. Reality: it usually breaks playback or does nothing, and changes over time.
• Myth: encrypted DNS changes the picture. Reality: encryption hides lookups from the network, but the resolver still sees only domain names.

Summary

DNS blocking cannot stop YouTube ads because the ads and the videos come from the same domains. Lists that claim otherwise usually do nothing or break playback. Use DNS filtering for what it does well, security and broad ad and tracker reduction across the network, and use browser extensions or an ad-free subscription for first-party video ads.