Gossip Protocol
Also: gossip
network · intermediate
How nodes propagate information — transactions, blocks, channel announcements — by telling a few peers, who tell a few more, until everyone has it.
Bitcoin and Lightning both use gossip. The network has no central broker; every node knows about a handful of peers and forwards new things to them. Within a few hops, news has spread to most of the network. This is robust against attackers censoring any single point — you'd have to suppress propagation at every peer's peer.
In Bitcoin Core, transactions are relayed via the inv / getdata protocol — peers exchange short inventory vectors of what they have, then request only what's new. Erlay (BIP-330, partially deployed) further reduces bandwidth by batching set-reconciliation rather than per-transaction announcements.
Lightning gossip works similarly but the payload is different: channel announcements (a channel exists between these two nodes), channel updates (fee policy, available capacity hints), and node announcements (this is my alias, my IPs). The gossip graph is what trampoline-less routing depends on.