Crypto glossary
Gossip protocol (P2P network)
A gossip protocol is how nodes spread transactions and blocks: each passes new data to a few peers, who pass it on until the whole network has it.
Public blockchains have no central server to distribute data. Each node keeps connections to a handful of peers, and when it receives a valid new transaction or block it forwards it to them. Like a rumour moving through a crowd, the information reaches thousands of nodes in seconds. Bitcoin nodes default to a limited number of outbound connections, while Ethereum's consensus layer uses a gossip system based on libp2p.
Propagation speed matters. Slow block relay increases the chance of competing blocks and gives an edge to large, well-connected miners or validators. Techniques such as compact blocks, which send only short transaction identifiers, and dedicated relay networks were developed to make gossip faster and lighter.
The peer-to-peer layer is also an attack surface. In an eclipse attack, an adversary surrounds a node with its own peers and feeds it a false view of the chain. Gossip can leak privacy, since the first node to relay a transaction is often its sender, and protocols such as Dandelion and the use of Tor try to hide that origin.
Example
A wallet broadcasts a transaction to one node; that node passes it to eight peers, each of them to their own peers, and within a few seconds most mempools in the network contain it.