How DNS, Firewalls and Endpoint Tools Block Websites

When a website block works, the request has been stopped at a particular point. The domain may never resolve to an IP address, the connection may be rejected before leaving the device, or endpoint software may prevent the browser or application from reaching the destination.

Each method works with different information. DNS filters inspect domain queries, basic firewall rules inspect network addresses and ports, TLS filters may read hostnames during connection setup, and endpoint tools can use information about the application making the request.

Understanding those differences explains why a website may remain accessible even when a filtering service reports that its rules are active.

Blocking Through the Hosts File and DNS

The earliest decision can happen on the device itself. Before contacting a DNS resolver, an operating system may check its local hosts file. On Linux and other Unix-like systems, this is usually /etc/hosts. Windows uses %SystemRoot%\System32\drivers\etc\hosts.

An...

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