p2p – Is Bitcoins’ peer-to-peer network unstructured or structured?
The Bitcoin network is unstructured.
Wikipedia describes it like this
Unstructured peer-to-peer networks do not impose a particular structure on the overlay network by design, but rather are formed by nodes that randomly form connections to each other. (Gnutella, Gossip, and Kazaa are examples of unstructured P2P protocols).
Bitcoin uses a specific variety of gossip protocol.
The Bitcoin network is mostly layered on the Internet Protocol (IP) network which is structured in the sense of routing vs bridging. As Wikipedia puts it
Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is still widely used within localized environments.