Is the network ID truly unique? It's hard to believe this, as it's just an integer.

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    Someone will probably chime in with a more detailed explanation. In summary, they have different Genesis Blocks and disregard each other. Mar 16, 2017 at 15:40

1 Answer 1


A geth node must have the same networkid as well as the same genesis block in order to join a network. The geth node also needs to know the enodeid of the peers you want to connect to. The geth client has a hardcoded list of bootnodes for the mainnet and official testnets.

You'll simply be connected to a different network if you have the same networkid but the genesis block is different.

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