  The peer-to-peer (P2P) network of blockchain used to transport its
transactions and blocks has a high impact on the efficiency and security of the
system. The P2P network topologies of popular blockchains such as Bitcoin and
Ethereum, therefore, deserve our highest attention. The current Ethereum
blockchain explorers (e.g., Etherscan) focus on the tracking of block and
transaction records but omit the characterization of the underlying P2P
network. This work presents the Ethereum Network Analyzer (Ethna), a tool that
probes and analyzes the P2P network of the Ethereum blockchain. Unlike Bitcoin
that adopts an unstructured P2P network, Ethereum relies on the Kademlia DHT to
manage its P2P network. Therefore, the existing analytical methods for
Bitcoin-like P2P networks are not applicable to Ethereum. Ethna implements a
novel method that accurately measures the degrees of Ethereum nodes.
Furthermore, it incorporates an algorithm that derives the latency metrics of
message propagation in the Ethereum P2P network. We ran Ethna on the Ethereum
Mainnet and conducted extensive experiments to analyze the topological features
of its P2P network. Our analysis shows that the Ethereum P2P network possesses
a certain effect of small-world networks, and the degrees of nodes follow a
power-law distribution that characterizes scale-free networks.
