The Bitcoin peer-to-peer network port — full nodes gossip blocks and transactions here.
Bitcoin Core listens on TCP 8333 for mainnet peer connections; bitcoin.org's full-node guide states the port and notes that supporting the network requires allowing inbound connections through your router and firewall. A node makes outbound peer connections on its own, so an open 8333 specifically means the host is willing to accept peers. Testnet and other networks use different ports, and the protocol is unauthenticated and public by design — anyone may connect and request blocks.
Fine to expose
Public exposure is the point: an inbound-reachable node is what serves blocks to other peers. The RPC port (8332) is the one that must never be public.
$ nc -vz TARGET 8333Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.