Updated on March 22, 2020

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.

Note

EIP-155 introduced using the chain ID as part of the transaction signing process to protect against transaction replay attacks.

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.

Chain ID 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.

Network	Chain	Chain ID	Network ID	Type
mainnet	ETH	1	1	Production
ropsten	ETH	3	3	Test
rinkeby	ETH	4	4	Test
goerli	ETH	5	5	Test
dev	ETH	2018	2018	Development
classic	ETC	61	1	Production
mordor	ETC	63	7	Test
kotti	ETC	6	6	Test

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.