گره کامل در Blockchain: | Full node in Blockchain:
Full node in Blockchain:
Any computer that connects to the Bitcoin network is called a node.
Nodes that fully verify all of the rules of Bitcoin are called full nodes.
The most popular software implementation of full nodes is called Bitcoin Core, its latest release can be found on the github page.
What makes a full node?
Here are examples of consensus rules, though there are many more:
Blocks may only create a certain number of bitcoins.
(Currently 6.25 BTC per block.)
Transactions must have correct signatures for the bitcoins being spent.
Transactions/blocks must be in the correct data format.
Within a single block chain, a transaction output cannot be double-spent.
If a transaction or block violates the consensus rules, then it is absolutely rejected, even if every other node on the network thinks that it is valid.
For full nodes, miners actually have fairly limited power: they can only reorder or remove transactions, and only by spending a lot of computing power.
A powerful miner is able to execute some serious attacks, but because full nodes rely on miners only for a few things, miners could not completely change or destroy Bitcoin.
Nodes that have different consensus rules are actually using two different networks/currencies.
Changing any of the consensus rules requires a hard fork, which can be thought of as creating a new currency and having everyone move to it.
Consensus rules are different from policy rules, which specify how a node or miner prioritizes or discourages certain things.
Policy rules can be changed freely, and different nodes can have different policy rules.
Because all full nodes must use exactly the same consensus rules in order to remain compatible with each other, even duplicating bugs and oddities in the original consensus rules, creating a full node from scratch is extremely difficult and dangerous.
It is therefore recommended that everyone who wishes to run a full node uses software based on the reference client, which is the only client guaranteed to behave correctly.
At minimum, a full node must download every transaction that has ever taken place, all new transactions, and all block headers.
Additionally, full nodes must store information about every unspent transaction output until it is spent.
By default full nodes are inefficient in that they download each new transaction at least twice, and they store the entire block chain (more than 165 GB as of 20180214) forever, even though only the unspent transaction outputs (<2 GB) are required.
Performance can improved by enabling -blocksonly mode and enabling pruning.
A subset of full nodes also accept incoming connections and upload old blocks to other peers on the network.
This happens if the software is run with -listen=1 as is default.
Contrary to some popular misconceptions, being an archival node is not necessary to being a full node.
Why should you use a full node wallet:
Running a full node is the only way you can use Bitcoin in a trustless way.
You will know for sure that all the rules of Bitcoin are being followed, for example that no bitcoins are spent not belonging to the owner, that no coins were spent twice, that no inflation happens outside of the schedule and that all the rules needed to make the system work (e.g.difficulty) are followed.
Full nodes are currently the most private way to use Bitcoin, with nobody else learning which bitcoin addresses belong to you.
Full nodes are the most secure way to use Bitcoin, they do not suffer from many attacks that affect lightweight wallets.
This is by far the most important reason for running a full node, though it is a little difficult to understand.
As explained previously, full nodes enforce the consensus rules no matter what.
However, lightweight nodes do not do this.
Lightweight nodes do whatever the majority of mining power says.
Therefore, if most of the miners got together to increase their block reward, for example, lightweight nodes would blindly go along with it.
If this ever happened, the network would split such that lightweight nodes and full nodes would end up on separate networks, using separate currencies.
People using lightweight nodes would be unable to transact with people using full nodes.
However, if almost everyone on the network is using lightweight nodes in this situation, then everyone would continue being able to transact with each other, and so Bitcoin could very well end up "hijacked" by evil miners.
In practice, miners are unlikely to attempt anything like the above scenario as long as full nodes are prevalent because the miners would lose a lot of money.
But the incentives completely change if everyone uses lightweight nodes.
It is only reasonably secure to use a lightweight node because most of the Bitcoin economy uses full nodes.
This is especially important for Bitcoin businesses, which have more economic weight.
Downloading the entire blockchain is the most private way to operate a wallet.
All other lightweight solutions leak information about which addresses are yours because they must query third-party servers.
The Electrum servers will know which addresses belong to you and can link them together.
Despite bloom filtering, SPV nodes based on BitcoinJ do not provide much privacy against nodes who connected directly to the wallet .
For some use cases, such privacy may not be required.
But an important reason to run a full node and use it as a wallet is to get the full privacy benefits.
Lightweight nodes are sometimes able to be temporarily tricked into accepting transactions or blocks that are not actually valid.
This could cause serious financial damage, especially for websites that automatically process Bitcoin transactions.
Full nodes provide the maximum security possible, and so they should be used by all businesses, and also by regular users whenever doing so is convenient.
Full nodes may provide various services to other network participants (if the software is run with -listen=1 as is default).
This is especially important for lightweight nodes.
These services include:
Filtering transactions and blocks on behalf of lightweight nodes so that lightweight nodes do not need to download every transaction ever made on the network in order to find their own transactions.
Serving historical full blocks to nodes that have been offline for a while.
Transmitting new transactions from users to miners.
Broadcasting new blocks from miners to other nodes.
For the most part, these services are only usefully performed by full nodes that are listening on port 8333.
The more full nodes that accept incoming connections there are, the more users the Bitcoin network can support.
Although if there is ever a shortage, lots of archival nodes can be easily created by cheaply renting VPS or AWS space.
Some are incentivizing it:
Bitnodes ran a program to incentivize full node operators until the end of 2015.How to run a full node:
If you run the Bitcoin Core/bitcoind wallet, you are running a full node.
There are a few alternate full node implementations, but they are not recommended for serious use because it is currently difficult to determine whether they implement the consensus rules with 100% accuracy.
Even very slight inaccuracies could cause serious problems for the users of these alternate clients.
Example of implementations Bitcore, libbitcoin, btcd.