296 lines
12 KiB
Markdown
296 lines
12 KiB
Markdown
---
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title: Private Networks
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sort_key: B
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---
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This guide explains how to set up a private network of multiple Geth nodes. An Ethereum
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network is a private network if the nodes are not connected to the main network. In this
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context private only means reserved or isolated, rather than protected or secure.
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### Choosing A Network ID
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The network ID is an integer number which isolates Ethereum peer-to-peer networks.
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Connections between blockchain nodes will occur only if both peers use the same genesis
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block and network ID. Use the `--networkid` command line option to set the network ID used
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by geth.
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The main network has ID 1. If you supply your own custom network ID which is different
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than the main network, your nodes will not connect to other nodes and form a private
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network. If you're planning to connect to your private chain on the Internet, it's best to
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choose a network ID that isn't already used. You can find a community-run registry of
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Ethereum networks at <https://chainid.network>.
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### Choosing A Consensus Algorithm
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While the main network uses proof-of-work to secure the blockchain, Geth also supports the
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the 'clique' proof-of-authority consensus algorithm as an alternative for private
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networks. We strongly recommend 'clique' for new private network deployments because it is
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much less resource intensive than proof-of-work. The clique system is also used for
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several public Ethereum testnets such as [Rinkeby](https://rinkeby.io) and
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[Görli](https://goerli.net).
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Here are the key differences between the two consensus algorithms available in Geth:
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Ethash consensus, being a proof-of-work algorithm, is a system that allows open
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participation by anyone willing to dedicate resources to mining. While this is a great
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property to have for a public network, the overall security of the blockchain strictly
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depends on the total amount of resources used to secure it. As such, proof-of-work is a
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poor choice for private networks with few miners. The Ethash mining 'difficulty' is
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adjusted automatically so that new blocks are created approximately 12 seconds apart. As
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more mining resources are deployed on the network, creating a new block becomes harder so
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that the average block time matches the target block time.
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Clique consensus is a proof-of-authority system where new blocks can be created by
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authorized 'signers' only. The clique consenus protocol is specified in
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[EIP-225](clique-eip). The initial set of authorized signers is configured in the genesis
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block. Signers can be authorized and de-authorized using a voting mechanism, thus allowing
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the set of signers to change while the blockchain operates. Clique can be configured to
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target any block time (within reasonable limits) since it isn't tied to the difficulty
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adjustment.
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[clique-eip]: https://eips.ethereum.org/EIPS/eip-225
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### Creating The Genesis Block
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Every blockchain starts with the genesis block. When you run Geth with default settings
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for the first time, it commits the main net genesis to the database. For a private
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network, you usually want a different genesis block.
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The genesis block is configured using the _genesis.json_ file. When creating a genesis
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block, you need to decide on a few initial parameters for your blockchain:
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- Ethereum platform features enabled at launch (`config`). Enabling protocol features
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while the blockchain is running requires scheduling a hard fork.
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- Initial block gas limit (`gasLimit`). Your choice here impacts how much EVM computation
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can happen within a single block. We recommend using the main Ethereum network as a
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[guideline to find a good amount](gaslimit-char). The block gas limit can be adjusted
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after launch using the `--targetgaslimit` command-line flag.
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- Initial allocation of ether (`alloc`). This determines how much ether is available to
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the addresses you list in the genesis block. Additional ether can be created through
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mining as the chain progresses.
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[gaslimit-chart]: https://etherscan.io/chart/gaslimit
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#### Clique Example
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This is an example of a genesis.json file for a proof-of-authority network. The `config`
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section ensures that all known protocol changes are available and configures the 'clique'
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engine to be used for consensus.
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Note that the initial signer set must be configured through the `extradata` field. This
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field is required for clique to work.
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First create the signer account keys using the [geth account](./managing-your-accounts)
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command (run this command multiple times to create more than one signer key).
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```shell
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geth account new --datadir data
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```
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Take note of the Ethereum address printed by this command.
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To create the initial extradata for your network, collect the signer addresses and encode
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`extradata` as the concatenation of 32 zero bytes, all signer addresses, and 65 further
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zero bytes. In the example below, `extradata` contains a single initial signer address,
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`0x7df9a875a174b3bc565e6424a0050ebc1b2d1d82`.
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You can use the `period` configuration option to set the target block time of the chain.
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```json
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{
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"config": {
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"chainId": 15,
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"homesteadBlock": 0,
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"eip150Block": 0,
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"eip155Block": 0,
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"eip158Block": 0,
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"byzantiumBlock": 0,
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"constantinopleBlock": 0,
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"petersburgBlock": 0,
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"clique": {
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"period": 5,
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"epoch": 30000
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}
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},
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"difficulty": "1",
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"gasLimit": "8000000",
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"extradata": "0x00000000000000000000000000000000000000000000000000000000000000007df9a875a174b3bc565e6424a0050ebc1b2d1d820000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
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"alloc": {
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"7df9a875a174b3bc565e6424a0050ebc1b2d1d82": { "balance": "300000" },
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"f41c74c9ae680c1aa78f42e5647a62f353b7bdde": { "balance": "400000" }
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}
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}
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```
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#### Ethash Example
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Since ethash is the default consensus algorithm, no additional parameters need to be
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configured in order to use it. You can influence the initial mining difficulty using the
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`difficulty` parameter, but note that the difficulty adjustment algorithm will quickly
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adapt to the amount of mining resources you deploy on the chain.
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```json
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{
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"config": {
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"chainId": 15,
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"homesteadBlock": 0,
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"eip150Block": 0,
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"eip155Block": 0,
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"eip158Block": 0,
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"byzantiumBlock": 0,
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"constantinopleBlock": 0,
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"petersburgBlock": 0,
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"ethash": {}
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},
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"difficulty": "1",
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"gasLimit": "8000000",
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"alloc": {
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"7df9a875a174b3bc565e6424a0050ebc1b2d1d82": { "balance": "300000" },
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"f41c74c9ae680c1aa78f42e5647a62f353b7bdde": { "balance": "400000" }
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}
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}
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```
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### Initializing the Geth Database
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To create a blockchain node that uses this genesis block, run the following command. This
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imports and sets the canonical genesis block for your chain.
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```shell
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geth init --datadir data genesis.json
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```
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Future runs of geth using this data directory will use the genesis block you have defined.
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```shell
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geth --datadir data --networkid 15
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```
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### Scheduling Hard Forks
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As Ethereum protocol development progresses, new Ethereum features become available. To
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enable these features on your private network, you must schedule a hard fork.
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First, choose any future block number where the hard fork will activate. Continuing from
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the genesis.json example above, let's assume your network is running and its current block
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number is 35421. To schedule the 'Istanbul' fork, we pick block 40000 as the activation
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block number and modify our genesis.json file to set it:
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```json
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{
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"config": {
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...
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"istanbulBlock": 40000,
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...
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},
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...
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}
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```
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In order to update to the new fork, first ensure that all Geth instances on your private
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network actually support the Istanbul fork (i.e. ensure you have the latest version of
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Geth installed). Now shut down all nodes and re-run the `init` command to enable the new
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chain configuration:
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```shell
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geth init --datadir data genesis.json
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```
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### Setting Up Networking
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Once your node is initialized to the desired genesis state, it is time to set up the
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peer-to-peer network. Any node can be used as an entry point. We recommend dedicating a
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single node as the rendezvous point which all other nodes use to join. This node is called
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the 'bootstrap node'.
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First, determine the IP address of the machine your bootstrap node will run on. If you are
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using a cloud service such as Amazon EC2, you'll find the IP of the virtual machine in the
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management console. Please also ensure that your firewall configuration allows both UDP
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and TCP traffic on port 30303.
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The bootstrap node needs to know about its own IP address in order to be able to relay it
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others. The IP is set using the `--nat` flag (insert your own IP instead of the example
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address below).
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```shell
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geth --datadir data --networkid 15 --nat extip:172.16.254.4
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```
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Now extract the 'node record' of the bootnode using the JS console.
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```shell
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geth attach data/geth.ipc --exec admin.nodeInfo.enr
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```
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This command should print a base64 string such as the following example. Other nodes will
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use the information contained in the bootstrap node record to connect to your peer-to-peer
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network.
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```text
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"enr:-Je4QEiMeOxy_h0aweL2DtZmxnUMy-XPQcZllrMt_2V1lzynOwSx7GnjCf1k8BAsZD5dvHOBLuldzLYxpoD5UcqISiwDg2V0aMfGhGlQhqmAgmlkgnY0gmlwhKwQ_gSJc2VjcDI1NmsxoQKX_WLWgDKONsGvxtp9OeSIv2fRoGwu5vMtxfNGdut4cIN0Y3CCdl-DdWRwgnZf"
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```
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Setting up peer-to-peer networking depends on your requirements. If you connect nodes
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across the Internet, please ensure that your bootnode and all other nodes have public IP
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addresses assigned, and both TCP and UDP traffic can pass the firewall.
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If Internet connectivity is not required or all member nodes connect using well-known IPs,
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we strongly recommend setting up Geth to restrict peer-to-peer connectivity to an IP
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subnet. Doing so will further isolate your network and prevents cross-connecting with
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other blockchain networks in case your nodes are reachable from the Internet. Use the
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`--netrestrict` flag to configure a whitelist of IP networks:
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```shell
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geth <other-flags> --netrestrict 172.16.254.0/24
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```
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With the above setting, Geth will only allow connections from the 172.16.254.0/24 subnet,
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and will not attempt to connect to other nodes outside of the set IP range.
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### Running Member Nodes
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With the bootnode operational and externally reachable (you can try `telnet <ip> <port>`
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to ensure it's indeed reachable), you can start more Geth nodes and connect them via the
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bootstrap node using the `--bootnodes` flag.
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To create a member node running on the same machine as the bootstrap node, choose a
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separate data directory (example: `data-2`) and listening port (example: `30305`):
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```shell
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geth --datadir data-2 --networkid 15 --port 30305 --bootnodes <bootstrap-node-record>
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```
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With the member node running, you can check whether it is connected to the bootstrap node
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or any other node in your network by attaching a console and running `admin.peers`. It may
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take up to a few seconds for the nodes to get connected.
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```shell
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geth attach data-2/geth.ipc --exec admin.peers
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```
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### Clique: Running A Signer
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To set up Geth for signing blocks in proof-of-authority mode, a signer account must be
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available. The account must be unlocked to mine blocks. The following command will prompt
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for the account password, then start signing blocks:
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```shell
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geth <other-flags> --unlock 0x7df9a875a174b3bc565e6424a0050ebc1b2d1d82 --mine
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```
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You can further configure mining by changing the default gas limit blocks converge to
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(with `--targetgaslimit`) and the price transactions are accepted at (with `--gasprice`).
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### Ethash: Running A Miner
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For proof-of-work in a simple private network, a single CPU miner instance is enough to
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create a stable stream of blocks at regular intervals. To start a Geth instance for
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mining, run it with all the usual flags and add the following to configure mining:
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```shell
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geth <other-flags> --mine --minerthreads=1 --etherbase=0x0000000000000000000000000000000000000000
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```
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This will start mining bocks and transactions on a single CPU thread, crediting all block
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rewards to the account specified by `--etherbase`.
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