What Is Node Discovery?

In peer-to-peer networks with no central server, a newly started node does not know how to reach the rest of the network. For this reason, client software includes predefined starting points: DNS seeds and hardcoded address lists in Bitcoin, and bootnodes in Ethereum. After connecting to these points, the node learns the addresses of other peers and expands its connection list.

Ethereum's discovery protocols are based on the distributed hash table (DHT) approach called Kademlia. Nodes map out the network step by step by asking each other for peers close to their own ID. Ethereum Node Records (ENR), a core part of discv5, let a node announce which network it runs on and with which capabilities; consensus layer clients also find their peers with this protocol.

Node discovery matters for network security. In a method known as an eclipse attack, the attacker tries to isolate the target node from the rest of the network and feed it false information by filling its connections with nodes under the attacker's control. Randomness in the discovery process, connection diversity, and limits on addresses coming from the same network block are measures used to make such attacks harder.