Each Ethereum stack selects one or more transports, and the transport fixes the framing, ports, and session setup of everything above it.
| Stack | Transport |
|---|---|
| devp2p (execution) | RLPx over TCP |
| discovery v4 and v5 | UDP datagrams |
| consensus libp2p | QUIC (primary) over UDP, TCP fallback |
| portal | uTP over discv5 |
RLPx is the TCP-based transport protocol for execution-layer peers. Discovery v4 and v5 send their messages as UDP datagrams. Consensus clients MUST support the QUIC (UDP) and TCP libp2p transports for dialing and listening, with QUIC as the primary transport. Portal runs its own framing over uTP sessions established through discv5.
The TCP, UDP, QUIC, and uTP pages state each transport's contract.