Comprehensive Guide to Ad Blocking: Techniques for a Cleaner Internet Experience

In the modern digital landscape, online advertising is ubiquitous, ranging from unobtrusive banners to intrusive pop-ups and video ads. While some level of advertising is tolerable, many users seek ways to eliminate disruptive and malicious ads. This article provides a detailed exploration of various ad-blocking techniques, balancing theory with practical implementation, suitable for users ranging from casual internet surfers to network administrators.

Understanding Ad Delivery Mechanisms

To effectively block ads, it’s crucial to understand how they are delivered. Ads are often loaded through JavaScript code embedded in websites, fetching content from specific ad servers. Analyzing website source code and network requests can reveal these ad delivery pathways.

Computer screen displaying website source code with highlighted ad script

DNS-Based Ad Blocking

One approach to ad blocking involves manipulating the Domain Name System (DNS). By preventing a device from resolving the domain names of ad servers, the ads cannot be loaded. This method can be implemented at the router level, affecting all devices on the network. Tools like dnsmasq, AdGuard Home, and even DNS modules within proxy tools like Xray and Sing-box can be utilized.

How it Works: DNS-based ad blocking essentially “poisons” the DNS resolution of known ad domains, pointing them to invalid IP addresses (e.g., 0.0.0.0).
Implementation: In dnsmasq, this involves specifying domain-to-IP mappings for ad servers.
Limitations: DNS-based blocking is limited because it blocks entire domains. If a domain serves both ads and legitimate content, the entire domain will be blocked.

While DNS-based ad blocking is a starting point, its effectiveness is limited, making it less preferred compared to other methods.

Host-Based Ad Blocking via Proxy Tools

Modern proxy tools such as Sing-box and OpenClash offer more sophisticated ad-blocking capabilities. They operate by inspecting the “host” field in HTTP requests after the DNS resolution, allowing for more granular control.

Screenshot of Sing-box configuration interface showing ad-blocking rules

How it Works: After the DNS resolution, the proxy tool checks the target website’s host against a list of known ad domains. If a match is found, the request is blocked.
Implementation (Sing-box): Using Homeproxy, users can define rulesets containing lists of ad domains. These rulesets are then applied to routing rules, blocking any traffic destined for those domains.
Implementation (OpenClash): OpenClash allows users to add additional rules that leverage external lists of ad domains, rejecting connections to those domains.

MITM (Man-in-the-Middle) Ad Blocking

For ads served from the same domain as legitimate content, more advanced techniques are required. MITM ad blocking intercepts and inspects encrypted HTTPS traffic, enabling the filtering of ads based on content.

Diagram illustrating the MITM ad blocking process with a proxy tool decrypting and inspecting HTTPS traffic

To implement MITM, a proxy tool decrypts HTTPS traffic, inspects the content for ads, and then re-encrypts the traffic before sending it to the destination server. This process requires installing a Certificate Authority (CA) certificate on the client device to allow the proxy to decrypt the traffic.

iOS Implementation (Shadowrocket): Users generate and install a CA certificate. The data is then decrypted and rules are written to reject traffic containing ads.
Limitations: MITM requires significant computational resources due to the encryption and decryption processes. It also raises privacy concerns, as the proxy tool has access to decrypted traffic.

Browser-Based Ad Blocking

Browser extensions offer a convenient and powerful way to block ads. These extensions operate within the browser, inspecting and filtering HTTP traffic before it is rendered.

Advantages: Browser extensions can easily remove ad elements from web pages without requiring complex configurations.
Functionality: They use filter lists and rules to identify and block ad content, often allowing users to create custom rules.
Example: AdGuard browser extension.

While effective, browser extensions can also introduce privacy risks if the extension is malicious. Users should exercise caution when installing browser extensions, ensuring they come from reputable sources.

Conclusion

Ad blocking is a multifaceted field with a range of techniques available, each with its own strengths and limitations. From basic DNS-based blocking to advanced MITM techniques, users can tailor their approach to achieve a cleaner and more enjoyable internet experience. While ethical considerations surrounding ad blocking exist, the methods discussed here empower users to take control of their online experience.