Open-source ESP32-C3 DNS ad blocker supports over 500K domains without PSRAM

So, if you want to use a locked down router, this device adds a blocklist, and you resolve your systems DNS requests through it, via wifi.

Personally, i'd just get a different router, although for $2, its a cheap stop gap.

"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."

"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 lookup takes around 10 ms (including WiFi round-trip time), requiring about 18 flash reads."

Nice demonstration of an embedded software technique, to create a device I can't imagine a practical use for, although I'm sure someone else can.