I know how to split but I'd like to know if, technically, all transactions on the Ethereum chain are automatically broadcasted on the "Ethereum Classic" chain and vice-versa or if replay "attacks" have to be specifically made by someone.
The one transaction I did to test it out, without using any splitter contract, was nearly instantly carried out on both chain. It was moreover valid on both chain, so the transaction happened on both chain (which was fine: it was just a test, with adresses I control).
So my question is: are all transactions automatically broadcasted to both chains and, for each chain, only those who are valid executed, or are there bots automatically replaying some (or all) the transactions?