Network ID and chain ID

Ethereum networks have two identifiers, a network ID and a chain ID. Although they often have the same value, they have different uses.

Peer-to-peer communication between nodes uses the network ID, while the transaction signature process uses the chain ID.

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

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

Besu sets the chain ID (and by default the network ID) automatically, using either the --genesis-file option or when specifying a network using the --network option. The following table lists the available networks and their chain and network IDs.

Specify a different network ID

Usually the network ID is the same as the chain ID, but if you want to separate specific nodes from the rest of the network so they can’t connect or synchronize with other nodes, you can override the default network ID for those nodes using the --network-id option.