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Create a private network using Ethash

A private network provides a configurable network for testing. By configuring a low difficulty and enabling mining, this allows for fast block creation.

You can test multi-block and multi-user scenarios on a private network before moving to one of the public testnets.

danger

The steps in this tutorial create an isolated, but not protected or secure, Ethereum private network. We recommend running the private network behind a properly configured firewall.

Prerequisites​

Steps​

Listed on the right-hand side of the page are the steps to create a private network using Ethash.

1. Create directories​

Each node requires a data directory for the blockchain data. When the node starts, Besu saves the node key in this directory.

Create directories for your private network, each of the three nodes, and a data directory for each node:

Private-Network/
├── Node-1
│   ├── data
├── Node-2
│   ├── data
└── Node-3
    ├── data

2. Create a genesis file​

The genesis file defines the genesis block of the blockchain (that is, the start of the blockchain). The genesis file includes entries for configuring the blockchain, such as the mining difficulty and initial accounts and balances.

All nodes in a network must use the same genesis file. The network ID defaults to the chainID in the genesis file. The fixeddifficulty enables fast block mining.

Copy the following genesis definition to a file called privateNetworkGenesis.json and save it in the Private-Network directory:

{
  "config": {
    "berlinBlock": 0,
    "ethash": {
      "fixeddifficulty": 1000
    },
    "chainID": 1337
  },
  "nonce": "0x42",
  "gasLimit": "0x1000000",
  "difficulty": "0x10000",
  "alloc": {
    "fe3b557e8fb62b89f4916b721be55ceb828dbd73": {
      "privateKey": "8f2a55949038a9610f50fb23b5883af3b4ecb3c3bb792cbcefbd1542c692be63",
      "comment": "private key and this comment are ignored.  In a real chain, the private key should NOT be stored",
      "balance": "0xad78ebc5ac6200000"
    },
    "f17f52151EbEF6C7334FAD080c5704D77216b732": {
      "privateKey": "ae6ae8e5ccbfb04590405997ee2d52d2b330726137b875053c36d94e974d162f",
      "comment": "private key and this comment are ignored.  In a real chain, the private key should NOT be stored",
      "balance": "90000000000000000000000"
    }
  }
}
note

We recommend specifying the latest milestone when creating the genesis file for a private network. This ensures you are using the most up-to-date protocol and have access to the most recent opcodes.

danger

Don't use the accounts in alloc in the genesis file on Mainnet or any public network except for testing. The private keys display, which means the accounts are not secure.

3. Start the first node as a bootnode​

Start Node-1:

besu --data-path=data --genesis-file=../privateNetworkGenesis.json --miner-enabled --miner-coinbase fe3b557e8fb62b89f4916b721be55ceb828dbd73 --rpc-http-enabled --host-allowlist="*" --rpc-http-cors-origins="all"

The command line enables:

info

The miner coinbase account is one of the accounts defined in the genesis file.

When the node starts, the enode URL displays. Copy the enode URL to specify Node-1 as the bootnode in the following steps.

Node 1 Enode URL

4. Start Node-2​

Start another terminal, change to the Node-2 directory and start Node-2 specifying the Node-1 enode URL copied when starting Node-1 as the bootnode:

besu --data-path=data --genesis-file=../privateNetworkGenesis.json --bootnodes=<Node-1 Enode URL> --p2p-port=30304

The command line specifies:

  • A different port to Node-1 for P2P discovery using the --p2p-port option.
  • The enode URL of Node-1 using the --bootnodes option.
  • A data directory for Node-2 using the --data-path option.
  • A genesis file as for Node-1.

5. Start Node-3​

Start another terminal, change to the Node-3 directory and start Node-3 specifying the Node-1 enode URL copied when starting Node-1 as the bootnode:

besu --data-path=data --genesis-file=../privateNetworkGenesis.json --bootnodes=<Node-1 Enode URL> --p2p-port=30305

The command line specifies:

  • A different port to Node-1 and Node-2 for P2P discovery.
  • A data directory for Node-3 using the --data-path option.
  • A bootnode and genesis file as for Node-2.

6. Confirm the private network is working​

Start another terminal, use curl to call the JSON-RPC API net_peerCount method and confirm the nodes are functioning as peers:

curl -X POST --data '{"jsonrpc":"2.0","method":"net_peerCount","params":[],"id":1}' localhost:8545

The result confirms Node-1 (the node running the JSON-RPC service) has two peers (Node-2 and Node-3):

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x2"
}

Next steps​

Import accounts to MetaMask and send transactions as described in the Quickstart tutorial.

info

Besu doesn't support private key management.

Send transactions using eth_sendRawTransaction to send ether or, deploy or invoke contracts.

Use the JSON-RPC API.

Start a node with the --rpc-ws-enabled option and use the RPC Pub/Sub API.

Stop the nodes​

When finished using the private network, stop all nodes using ++ctrl+c++ in each terminal window.

tip

To restart the private network in the future, start from 3. Start the first node as a bootnode.