Below are the number of reachable nodes as of 2021-10-19 10:10:03 UTC. Page refreshes automatically.
A Bitcoin node is a software or device that runs the Bitcoin protocol. Nodes contain the full or partially pruned database of all BTC transactions, originating all the way back to the Genesis Block to the latest block height of a valid block mined by a miner.
Nodes verify blockchain consensus rules by enforcing the core properties of the Bitcoin network. When a miner finishes a proof of work process, it then gets the ability to submit the found block onto the Bitcoin blockchain.
Before that happens, nodes must verify that the miner has found the correct hash that was set out as a requirement to find and submit the block that contains the transactions.
If everything is in order, then the block is put onto the blockchain, it will attach to the preceding block and all proceeding blocks will be attached to this block. The chain of blocks is called the blockchain.
Bitcoin nodes also serve an important role within the Bitcoin ecosystem. Due to their ability to enforce consensus rules, the nodes are of higher authority in the ecosystem due to their voluntary operational basis.
Although Bitcoin nodes can no longer mine blocks, they must cooperate with miners in order to include new blocks on the blockchain. When a miner produces a correct block, it receives a reward from the Bitcoin node network for finishing proof of work properly.
When a miner attempts to produce false blocks, the nodes reject those blocks and do not provide a block reward for false blocks.
Therefore, nodes are essential units of the defense mechanism of the Bitcoin network in relation to transaction processing, and act as a last line of defense against malicious miners.
Although a 51% attack could be used to produce blocks, the nature of the proof of work algorithm promotes adherence to the consensus rules to receive block rewards. Attacking the Bitcoin network comes with extremely high costs due to the expended energy that is required to produce the correct hashes that allow miners to submit blocks to nodes to include them on the blockchain
The map above shows concentration of reachable Bitcoin nodes found in countries around the world. The data is sourced using Bitnodes, which is currently being developed to estimate the size of the Bitcoin network by finding all the reachable nodes in the network.
The current methodology involves sending getaddr messages recursively to find all the reachable nodes in the network, starting from a set of seed nodes. Bitnodes uses Bitcoin protocol version 70001 (i.e. >= /Satoshi:0.8.x/), so nodes running an older protocol version will be skipped.