The peer node responds with +verack+ to acknowledge and establish a connection, and optionally sends its own +version+ message if it wishes to reciprocate the connection and connect back as a peer.
How does a new node find peers? Although there are no special nodes in bitcoin, there are some long-running stable nodes that are listed in the client as((("nodes","seed")))((("seed nodes"))) _seed nodes_. Although a new node does not have to connect with the seed nodes, it can use them to quickly discover other nodes in the network. In the Bitcoin Core client, the option to use the seed nodes is controlled by the option switch +-dnsseed+, which is set to 1, to use the seed nodes, by default. Alternatively, a bootstrapping node that knows nothing of the network must be given the IP address of at least one bitcoin node, after which it can establish connections through further introductions. The command-line argument +-seednode+ can be used to connect to one node just for introductions, using it as a DNS seed. After the initial seed node is used to form introductions, the client will disconnect from it and use the newly discovered peers.
[[network_handshake]]
.The initial handshake between peers
image::images/msbt_0604.png["NetworkHandshake"]
How does a new node find peers? Although there are no special nodes in bitcoin, there are some long-running stable nodes that are listed in the client as((("nodes","seed")))((("seed nodes"))) _seed nodes_. Although a new node does not have to connect with the seed nodes, it can use them to quickly discover other nodes in the network. In the Bitcoin Core client, the option to use the seed nodes is controlled by the option switch +-dnsseed+, which is set to 1, to use the seed nodes, by default. Alternatively, a bootstrapping node that knows nothing of the network must be given the IP address of at least one bitcoin node, after which it can establish connections through further introductions. The command-line argument +-seednode+ can be used to connect to one node just for introductions, using it as a DNS seed. After the initial seed node is used to form introductions, the client will disconnect from it and use the newly discovered peers.
Once one or more connections are established, the new node will send an((("addr message"))) +addr+ message containing its own IP address to its neighbors. The neighbors will, in turn, forward the +addr+ message to their neighbors, ensuring that the newly connected node becomes well known and better connected. Additionally, the newly connected node can send +getaddr+ to the neighbors, asking them to return a list of IP addresses of other peers. That way, a node can find peers to connect to and advertise its existence on the network for other nodes to find it. <<address_propagation>> shows the address discovery protocol.
myarbrough@oreilly.com
10 years ago