Updated 2019-10-02

Network ID and Chain ID

Ethereum networks have a network ID and a chain ID. The network ID defaults to the chain ID specified in the genesis file.

Chain ID in Genesis File

{
  "config": {
    "ethash": {
    },
     "chainID": 1981
  },
  ...
}

For most networks including MainNet and the public testnets, the network ID and the chain ID are the same and are specified in the genesis file.

The network ID and chain ID are automatically defined by Besu when connecting to networks specified using the --network option:

When using the --network=dev or --genesis-file options, you can override the network ID using the --network-id option.