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.
How does a new node find peers? The first method is to query DNS using a number of ((("nodes","seed")))((("DNS seed")))"DNS seeds", which are DNS servers that provide a list of IP addresses of bitcoin nodes. Some of those DNS seeds provide a static list of IP addresses of stable bitcoin listening nodes. Some of the DNS seeds are custom implementations of BIND (Berkeley Internet Name Daemon) that return a random subset from a list of bitcoin node addresses collected by a crawler or a long-running bitcoin node. The Bitcoin Core client contains the names of five different DNS seeds. The diversity of ownership and diversity of implementation of the different DNS seeds offers a high level or reliability for the initial bootstrapping process. In the Bitcoin Core client, the option to use the DNS seeds is controlled by the option switch +-dnsseed+, which is set to 1, to use the DNS seed, 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 seed. After the initial seed node is used to form introductions, the client will disconnect from it and use the newly discovered peers.
@ -123,7 +123,7 @@ During the development of the book, I made early drafts available on GitHub and
Once the book was drafted, it went through several rounds of technical review. Thanks to Cricket Liu and Lorne Lantz for their thorough review, comments, and support.
Several bitcoin developers contributed code samples, reviews, comments, and encouragement. Thanks to Amir Taaki and Eric Voskuil for example code snippets and many great comments; Vitalik Buterin and Richard Kiss for help with elliptic curve math and code contributions; Gavin Andresen for corrections, comments, and encouragement; and Michalis Kargakis for comments, contributions, and btcd writeup.
Several bitcoin developers contributed code samples, reviews, comments, and encouragement. Thanks to Amir Taaki and Eric Voskuil for example code snippets and many great comments; Vitalik Buterin and Richard Kiss for help with elliptic curve math and code contributions; Gavin Andresen for corrections, comments, and encouragement; Michalis Kargakis for comments, contributions, and btcd writeup; and Robin Inge for errata submissions improving the second print.
I owe my love of words and books to my mother, Theresa, who raised me in a house with books lining every wall. My mother also bought me my first computer in 1982, despite being a self-described technophobe. My father, Menelaos, a civil engineer who just published his first book at 80 years old, was the one who taught me logical and analytical thinking and a love of science and engineering.
Andreas M. Antonopoulos
9 years ago