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| − | #[[Peer-to-Peer Network Architecture]]
| + | The Bitcoin network is a made up of one (and only one) type of node that is defined in section 5 of the white paper. These nodes are often referred to as miners and are characterised by an ability to produce valid blocks, distribute them to their peers (other nodes), and validate blocks they receive. Nodes are responsible for upholding the consensus mechanism of the system based on block publication and proof-of-work. There is no other definition of a node in the Bitcoin network. |
| − | #[[Exchanging "Inventory"]]
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| − | #[[Simplified Payment Verification]]
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| − | #[[Encrypted and Authenticated Connections]]
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| − | #[[Transaction Pools]]
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| | + | * A node constructs, distributes and validates blocks |
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| | + | Old nodes may drop off the network and new nodes may join at any time. There is no hierarchy in the process of block distribution or validation, making the network truly peer-to-peer. Nodes are incentivised to maintain a high degree of connectivity with other nodes. This means that the network topology is that of a nearly complete graph. At any one time there are typically less than ten nodes that publish the majority of blocks. |
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| − | Bitcoin uses a simple broadcast network to propagate transactions and blocks. All communications are done over TCP. Bitcoin is fully able to use ports other than 8333 via the -port parameter. IPv6 is [https://bitcointalk.org/index.php?topic=81378.0 supported] with Bitcoind/Bitcoin-Qt v0.7. Using bitcoin over [[tor]] is also supported.
| + | [[File:nearly_complete_graph.png|thumb|300px|centre|An example of the bitcoin network with six nodes. The topology is that of a nearly complete graph.]] |
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| − | == Messages ==
| + | Bitcoin nodes also validate and propagate transactions. Transactions enter the network through users of the system. The users themselves are outside the Bitcoin network and interact with one or more Bitcoin nodes through client software. |
| − | * ''version'' - Information about program version and block count. Exchanged when first connecting.
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| − | * ''verack'' - Sent in response to a version message to acknowledge that we are willing to connect.
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| − | * ''addr'' - List of one or more IP addresses and ports.
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| − | * ''inv'' - "I have these blocks/transactions: ..." Normally sent only when a ''new'' block or transaction is being relayed. This is only a list, not the actual data.
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| − | * ''getdata'' - Request a single block or transaction by hash.
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| − | * ''getblocks'' - Request an ''inv'' of all blocks in a range.
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| − | * ''getheaders'' - Request a ''headers'' message containing all block headers in a range.
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| − | * ''tx'' - Send a transaction. This is sent only in response to a ''getdata'' request.
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| − | * ''block'' - Send a block. This is sent only in response to a ''getdata'' request.
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| − | * ''headers'' - Send up to 2,000 block headers. Non-generators can download the headers of blocks instead of entire blocks.
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| − | * ''getaddr'' - Request an ''addr'' message containing a bunch of known-active peers (for bootstrapping).
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| − | * ''submitorder'', ''checkorder'', and ''reply'' - Used when performing an [[IP address|IP transaction]].
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| − | * ''alert'' - Send a network alert.
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| − | * ''ping'' - Does nothing. Used to check that the connection is still online. A TCP error will occur if the connection has died.
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| − | More information and in-depth technical information is in the [[Protocol Specification]].
| + | * A user interacts with nodes through client software |
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| − | == Connection ==
| + | An example of a user may be a service provider, storage entity, propagation entity, autonomous agent (smart contract), or a wallet belonging to a person or business. Note that the users do not play a role in the production, distribution, or validation of blocks on the Bitcoin network. Therefore, they are not involved in the consensus process. |
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| − | To connect to a peer, you send a ''version'' message containing your version number, block count, and current time. The remote peer will send back a ''verack'' message and his own ''version'' message if he is accepting connections from your version. You will respond with your own ''verack'' if you are accepting connections from his version.
| + | The direct connection between users for the purpose of sending a transaction does not necessarily mean that they are part of any network. However, there may exist complex user networks that are separate to the Bitcoin network. A user may be a node on their own network whilst being a client on the Bitcoin network. Such networks may be thought of as being overlaid on top of the Bitcoin network. User networks may be peer-to-peer or hierarchical in structure, for example service providers and consumers. These user networks may be layered on top of one another in such a way that they form a [[Bitcoin Layered Networks|Bitcoin-Layered Network]]. |
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| − | The time data from all of your peers is collected, and the median is used by Bitcoin for all network tasks that use the time (except for other version messages).
| + | There is no requirement for a Bitcoin node to be made up of a single machine. A node may be made up of several different linked systems including routing, database and processing modules. However, there is no such thing as an archival or transaction propagation node on the Bitcoin network. |
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| − | You then exchange ''getaddr'' and ''addr'' messages, storing all addresses that you don't know about. ''addr'' messages often contain only one address, but sometimes contain up to 1000. This is most common at the beginning of an exchange.
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| − | == Standard relaying ==
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| − | When someone sends a transaction, they send an ''inv'' message containing it to all of their peers. Their peers will request the full transaction with ''getdata''. If they consider the transaction valid after receiving it, they will also broadcast the transaction to all of their peers with an ''inv'', and so on. Peers ask for or relay transactions only if they don't already have them. A peer will never rebroadcast a transaction that it already knows about, though transactions will eventually be forgotten if they don't get into a block after a while. The sender and receiver of the transaction will rebroadcast, however.
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| − | Anyone who is generating will collect valid received transactions and work on including them in a block. When someone does find a block, they send an ''inv'' containing it to all of their peers, as above. It works the same as transactions.
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| − | Everyone broadcasts an ''addr'' containing their own IP address every 24 hours. Nodes relay these messages to a couple of their peers and store the address if it's new to them. Through this system, everyone has a reasonably clear picture of which IPs are connected to the network at the moment. After connecting to the network, you get added to everyone's address database almost instantly because of your initial ''addr''.
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| − | Network alerts are broadcast with ''alert'' messages. No ''inv''-like system is used; these contain the entire alert. If a received alert is valid (signed by one of the people with the private key), it is relayed to all peers. For as long as an alert is still in effect, it is rebroadcast at the start of every new connection.
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| − | == Initial block download ==
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| − | At the start of a connection, you send a ''getblocks'' message containing the hash of the latest block you know about. If the peer doesn't think that this is the latest block, it will send an ''inv'' that contains up to 500 blocks ahead of the one you listed. You will then request all of these blocks with ''getdata'', and the peer will send them to you with ''block'' messages. After you have downloaded and processed all of these blocks, you will send another ''getblocks'', etc., until you have all of the blocks.
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| − | == Thin SPV Clients ==
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| − | [[BIP 0037]] introduced support for thin or lite clients by way of Simple Payment Verification. SPV clients do not need to download the full block contents to verify the existence of funds in the blockchain, but rely on the chain of block headers and bloom filters to obtain the data they need from other nodes. This method of client communication allows high security trustless communication with full nodes, but at the expensive of some privacy as the peers can deduce which addresses the SPV client is seeking information about.
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| − | [[MultiBit]] and [[Bitcoin Wallet]] work in this fashion using the library [[bitcoinj]] as their foundation.
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| − | == Bootstrapping ==
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| − | You choose which peers to connect to by sorting your address database by the time since you last saw the address and then adding a bit of randomization.
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| − | Bitcoin has three methods of finding peers.
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| − | === Addr ===
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| − | The ''addr'' messages described above create an effect similar to the IRC bootstrapping method. You know reasonably quickly whenever a peer joins, though you won't know for a while when they leave.
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| − | Bitcoin comes with a list of addresses known as "seed nodes". If you are unable to connect to IRC and you've never connected to the network before, the client will update the address database by connecting to one of the nodes from this list.
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| − | The -addnode command line option can be used to manually add a node. The -connect option can force bitcoin to connect only to a specific node.
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| − | === DNS ===
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| − | Bitcoin looks up the IP Addresses of several host names and adds those to the list of potential addresses. This is the default seeding mechanism, as of v0.6.x and later.
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| − | === IRC ===
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| − | As-of version 0.6.x of the Bitcoin client IRC bootstrapping is no longer enabled by default, and as of version 0.8.2 support for IRC bootstrapping has been removed completely. The information below is accurate for most versions prior.
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| − | Bitcoin joins a random channel between #bitcoin00 and #bitcoin99 on irc.lfnet.org. Your nick is set to an encoded form of your IP address. By decoding all the nicks of all users on the channel, you get a list of all IP addresses currently connected to Bitcoin.
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| − | For hosts that cannot make outbound connections on port 6667, the lfnet servers are also [[FAQ#Do_I_need_to_configure_my_firewall_to_run_bitcoin?|listening on port 7777]].
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| − | == Heartbeat ==
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| − | If thirty minutes or more has passed since the client has transmitted any messages it will transmit a message to keep the connection to the peer node alive.
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| − | If ninety minutes has passed since a peer node has communicated any messages, then the client will assume that connection has closed.
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| − | == See Also ==
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| − | * [[Protocol Specification]]
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| − | * [[Satoshi Client Node Discovery]]
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| − | * [http://bitcoinstatus.rowit.co.uk/ Historical Network Status (no longer updated)]
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| − | * [http://getaddr.bitnodes.io/ Bitnodes.io's network size estimate]
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| − | * [http://fullnode.info/howto.html How to run your own cheap full bitcoin node]
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| − | * [https://www.bitcoinmining.com/ Bitcoin Mining]
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| − | * [https://www.youtube.com/watch?v=GmOzih6I1zs Video: What is Bitcoin Mining]
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| − | [[Category:Technical]]
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| − | [[pl:Sieć]]
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The Bitcoin network is a made up of one (and only one) type of node that is defined in section 5 of the white paper. These nodes are often referred to as miners and are characterised by an ability to produce valid blocks, distribute them to their peers (other nodes), and validate blocks they receive. Nodes are responsible for upholding the consensus mechanism of the system based on block publication and proof-of-work. There is no other definition of a node in the Bitcoin network.
- A node constructs, distributes and validates blocks
Old nodes may drop off the network and new nodes may join at any time. There is no hierarchy in the process of block distribution or validation, making the network truly peer-to-peer. Nodes are incentivised to maintain a high degree of connectivity with other nodes. This means that the network topology is that of a nearly complete graph. At any one time there are typically less than ten nodes that publish the majority of blocks.
An example of the bitcoin network with six nodes. The topology is that of a nearly complete graph.
Bitcoin nodes also validate and propagate transactions. Transactions enter the network through users of the system. The users themselves are outside the Bitcoin network and interact with one or more Bitcoin nodes through client software.
- A user interacts with nodes through client software
An example of a user may be a service provider, storage entity, propagation entity, autonomous agent (smart contract), or a wallet belonging to a person or business. Note that the users do not play a role in the production, distribution, or validation of blocks on the Bitcoin network. Therefore, they are not involved in the consensus process.
The direct connection between users for the purpose of sending a transaction does not necessarily mean that they are part of any network. However, there may exist complex user networks that are separate to the Bitcoin network. A user may be a node on their own network whilst being a client on the Bitcoin network. Such networks may be thought of as being overlaid on top of the Bitcoin network. User networks may be peer-to-peer or hierarchical in structure, for example service providers and consumers. These user networks may be layered on top of one another in such a way that they form a Bitcoin-Layered Network.
There is no requirement for a Bitcoin node to be made up of a single machine. A node may be made up of several different linked systems including routing, database and processing modules. However, there is no such thing as an archival or transaction propagation node on the Bitcoin network.
