$5 ESP32 Blocks 537K Domains

Egyptian developer ZedAxis created a $5 ad-blocking DNS filter using an ESP32-C3 microcontroller, capable of storing 537,000 blocked domains. He overcame RAM limitations by hashing domain names and storing them in the device’s 4MB of flash memory. This allows the ESP32 to perform binary searches and block ads with around 10ms latency.

The project serves as a backup DNS server for ZedAxis’ home network, taking over when his primary Pi-hole system reboots or is unavailable. While not intended to replace comprehensive ad-blocking platforms like Pi-hole, it provides a low-power, cost-effective solution for maintaining ad-free browsing. The device can operate using only a USB port from an existing router for power.

ZedAxis achieved this by downloading public blocklists, removing duplicates, and using a 40-bit hashing algorithm. He can store roughly 537,000 domains if he disables over-the-air firmware updates, which would otherwise use some of the flash memory.