Open-source ESP32-C3 DNS ad blocker supports up to over 500,000 domains without PSRAM

Developed by Zed (M-Abozaid), the esp32-c3-adblock is an open-source, Pi-hole-style DNS ad blocker that runs on a $2 ESP32-C3 microcontroller board/module without requiring PSRAM. It blocks ads and tracking domains across devices on a home or small office network by filtering DNS requests. Instead of storing domain strings in RAM, the project stores them as sorted 40-bit FNV-1a hashes in flash memory and uses binary search to check DNS requests. When a UDP DNS query comes in, the C++ firmware extracts the domain, hashes it (including parent suffixes), and performs a binary search against the flash hash table. If the domain is on the blocklist, the ESP32-C3 returns 0.0.0.0 to block the request. Otherwise, it forwards the query to an upstream DNS server and returns the response to the client. This method fits over 140,000 domains into ~0.7 MB of flash memory while using only ~50 KB of RAM. A […]

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