ADNL (Abstract Datagram Network Layer) is TON's own networking protocol — the equivalent of TCP/IP for the blockchain. All node-to-node communication (validators, full nodes, light clients) happens on top of ADNL.
ADNL uses addresses derived from Ed25519 public keys, is independent of IP routing, and resilient to IP changes. DHT, RLDP, and ADNL tunnels are all built on top of it.