What is Ad Blocking?

DNS-based ad blocking operates during the domain resolution step that precedes every web connection:

• Domain lookup: When a page loads, the browser makes DNS queries for every domain referenced — including ad servers, tracking pixels, and analytics services
• Blocklist check: The DNS filter compares each queried domain against a blocklist of known advertising domains
• Blocked response: If the domain is on the blocklist, the resolver returns an NXDOMAIN or a redirect to a block page — the ad content never loads
• Allowed response: Legitimate page content domains resolve normally, so the website itself loads without interruption

Because this happens at the DNS layer, it works regardless of the browser, app, or device. It also reduces bandwidth usage since blocked ad content is never downloaded.

DNS-based ad blocking offers several advantages over browser-based solutions:

• Network-wide protection: Every device connected to the network (phones, tablets, smart TVs, IoT) is covered without per-device configuration
• Performance improvement: Blocking ads at DNS reduces page load times and saves bandwidth
• Privacy protection: Many ad networks track users across sites — blocking their domains also blocks tracking
• No software required: Works by changing DNS settings on your router — no apps or extensions needed

Limitations include the inability to block ads served from the same domain as page content (first-party ads) and the lack of cosmetic filtering (hiding empty ad placeholders on the page).

CleanBrowsing's DNS filtering includes ad blocking as part of its content filtering categories. With 21+ content categories available on paid plans, you can enable or disable ad blocking alongside other filtering rules.

For organizations managing website infrastructure, NOC.org provides authoritative DNS, CDN, and WAF services to protect the sites themselves — while CleanBrowsing protects the users browsing them.