DNS Filtering: What it is, why it helps, and how to set it up safely

DNS Filtering

Why it matters

Most threats start with a click. Stopping connections at the DNS layer cuts off malware downloads, command-and-control beacons, and fake login pages -without slowing users or breaking trusted sites.

How it works 

  • Your device asks DNS for a site’s address.

  • The resolver compares the domain to threat feeds and your rules.

  • Allowed domains resolve normally; blocked domains return nothing or a safe page.

  • Categories (malware, phishing, adult, piracy, crypto-mining) make policy easy.

Good uses

  • Security: block malware/phishing and C2 call-outs by default.

  • Compliance & productivity: restrict categories at work/school.

  • Home safety: filter adult content and scam sites across all devices.

Limits to know

  • Doesn’t see IP-only traffic or traffic sent through some VPNs.

  • Users can try alternate DNS unless you enforce it on the network.

  • False positives happen—keep an allowlist and review logs.

Quick setup 

  1. Pick a reputable DNS filtering service with categories and custom lists.

  2. Force all DNS to your resolver at the router/firewall; block outbound 53/853 to others.

  3. Enable DoH/DoT to your chosen resolver to prevent tampering.

  4. Start in monitor mode for a week, review hits, then enforce.

  5. Maintain allow/deny lists; alert on malware/phishing blocks.

    Glossary (A–Z)

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