EIP868 - Node Discovery v4 ENR Extension

# Abstract

This EIP defines an extension to Node Discovery Protocol v4 to enable authoritative resolution of Ethereum Node Records (ENR).

# Motivation

To bridge current and future discovery networks and to aid the implementation of other relay mechanisms for ENR such as DNS, we need a way to request the most up-to-date version of a node record. This EIP provides a way to request it using the existing discovery protocol.

# Specification

Implementations of Node Discovery Protocol v4 should support two new packet types, a request and reply of the node record. The existing ping and pong packets are extended with a new field containing the sequence number of the ENR.

# Ping Packet (0x01)

packet-data = [version, from, to, expiration, enr-seq]

enr-seq is the current sequence number of the sending node's record. All other fields retain their existing meaning.

# Pong Packet (0x02)

packet-data = [to, ping-hash, expiration, enr-seq]

enr-seq is the current sequence number of the sending node's record. All other fields retain their existing meaning.

# ENRRequest Packet (0x05)

packet-data = [ expiration ]

When a packet of this type is received, the node should reply with an ENRResponse packet containing the current version of its record.

To guard against amplification attacks, the sender of ENRRequest should have replied to a ping packet recently (just like for FindNode). The expiration field, a UNIX timestamp, should be handled as for all other existing packets i.e. no reply should be sent if it refers to a time in the past.

# ENRResponse Packet (0x06)

packet-data = [ request-hash, ENR ]

This packet is the response to ENRRequest.

request-hash is the hash of the entire ENRRequest packet being replied to.
ENR is the node record.

The recipient of the packet should verify that the node record is signed by node who sent ENRResponse.

# Resolving Records

To resolve the current record of a node public key, perform a recursive Kademlia lookup using the FindNode, Neighbors packets. When the node is found, send ENRRequest to it and return the record from the response.