(Image credit: ZedAxis/YouTube)
How cheap can you build a hardware-based ad-blocking DNS filter? "Free," if you're willing to salvage some used hardware that's being thrown away. What if you aren't so lucky? In the era of the RAMageddon, even a Raspberry Pi will cost you a couple hundred bucks. But you know, you don't even need something that powerful. In fact, you can use a $5 microcontroller to build a fully functional ad-blocking filter with over 500,000 domains blocked and around 10ms latency.We know that's possible because Egyptian full-stack developer ZedAxis (@M-Abozaid on GitHub) has already built one. Using an ESP32-C3 "SuperMini" board, he's created a backup DNS for his home network that still provides ad blocking. His primary router is a Pi-hole, which is a Raspberry Pi running specialized software to manage DHCP addressing and DNS resolution with integrated ad-blocking. The SuperMini serves as a backup when the Pi-Hole is rebooting or otherwise unavailable.
The specific ESP32-C3 SuperMini board that ZedAxis used. (Image credit: ZedAxis/YouTube)Strictly speaking, we haven't seen ZedAxis' creation in action, but there's no reason to believe it doesn't work. The ESP32 family of embedded Wi-Fi-enabled microcontrollers is a well-known quantity, and this functionality is by no means outside the realm of its capabilities. In fact, this specific trick allows the use of the ESP32-C3, which is a cost-reduced version of the chip that doesn't have the 8MB of PSRAM found on some higher-end models. (There are MANY variants of the ESP32.)Instead, the ESP32-C3 used by ZedAxis has just 400KB of RAM, and 4MB of flash memory. With these limited specifications, he wasn't able to store a plaintext blocklist of any real size; it's simply too much data. So, he did what any enterprising hacker would do: he started hashing the data to reduce its size. Using 40-bit FNV-1a hashes, because 32-bit would give too many collisions and 64-bit wastes too much space, he can store some 537,000 domains in the flash memory of the device.
