URL filtering with Pi-hole

Into the Funnel

Article from Issue 274/2023

Supporting browser plug-ins, network-based DNS blockers like Pi-hole help protect you against online tracking and unwanted content.

One episode of the award-winning TV series Futurama depicts the Internet as a metaverse in which advertising banners attack users' avatars like birds of prey: "The Internet! My God! It's full of ads!" Even without a metaverse, Internet users today are tracked by trackers and cookies and flooded with unwanted advertising. But users can protect themselves against this flood of advertising. There are various methods of evading tracking by advertisers, confusing trackers, and keeping unwanted content out of websites. With the help of the free Pi-hole [1], this article looks at a couple of effective approaches that help protect you against unwanted content at the server, network, and client levels, while minimizing the threat of phishing at the same time.

Proxy Filter with Problems

In the early 2000s, the proxy filter was the best way to protect yourself against unwanted content and threats from viruses and Trojan Horses from the web. Clients do not request the content of a website directly from the web, but pass the request to a central proxy server such as Squid. The server then retrieves the content, stores some of it in a local cache, and returns the information to the browser. In times of limited bandwidth, proxies were popular mainly because of their caching function, which meant that less information needed to be retrieved over slow Internet connections. Plugins such as squidGuard blocked unwanted content at the proxy level, while other extensions inspected the content of websites directly and checked for malware.

The proxies' work was made more difficult by an important security feature: HTTPS. Encrypted protocols need to pass through a proxy server without change, meaning that their content cannot be filtered, unless you break the encryption. This method, SSL Bump, is still used, especially by large companies: The proxy server terminates the SSL connection of the accessed website and inspects, filters, and caches the decrypted content. For communication with the client browser, the proxy then encrypts the data again, but uses its own certificate for this purpose. For a scenario such as this, the administrator needs to modify the configurations of all the browsers on the LAN so they accept the proxy's certificate for all URLs.


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