The genesis file contains the necessary fields required for a custom genesis block. This is the first block in the network and does not point to any previous block. The Ethereum protocol performs checking in order to ensure that no other node on the internet can participate in the consensus mechanism unless they have the same genesis block. Chain ID is usually used as an identification of the network.
A custom genesis file that will be used later in the example is shown here:
{ "nonce": "0x0000000000000042", "timestamp": "0x00", "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000", "extraData": "0x00", "gasLimit": "0x8000000", "difficulty": "0x0400", "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000", ...
