Kademlia

A distributed hash table (DHT) using the XOR metric to provide efficient, decentralized node lookup and data storage.

Kademlia defines the architecture for decentralized peer-to-peer networks by treating node IDs as points in a 160-bit keyspace. Developed by Petar Maymounkov and David Mazières in 2002, it utilizes an XOR-based distance metric to calculate the 'closeness' between nodes, ensuring lookups resolve in O(log n) steps. This design powers massive systems like the BitTorrent Mainline DHT (supporting millions of concurrent users) and Ethereum's node discovery protocol. Its core strength lies in its resistance to churn: nodes update their routing tables (k-buckets) automatically during routine queries, maintaining network stability without heavy overhead.

https://pdos.csail.mit.edu/~petar/papers/maymounkov-kademlia-lncs.pdf