CAIP-2 (Blockchain references)

[axic]

@MicahZoltu

@ligi

Do you have any EIP/link where it was actually introduced?

I am pretty sure it has always been there and I think it is part of the genesis block (though it might be called Network ID in there because early on the two were conflated)? It is necessary to keep testnetworks and mainnet separate from each other, and then eventually (with the ETC split) to keep ETC separate from ETH.

I do not think it existed from beginning, hence on the Morden testnet, each new account had a starting nonce of 2^20 in order to differentiate transactions from mainnet transactions.