how does the magic number work for different era's?

Question

I'm a but confused with the magic number in the testnet:

• when we execute a transaction with the cli cardano-cli run transaction , we run it in the alonzo-era. when we check for the magic number, we have to check the networkMagic field in testnet-shelly-geneisis.json

There doesn't seem to be a networkMagic in testnet-alonzo-genesis.json, although there is in both the shelly and byron config files, and it's the same networkMagic in these two configs.

Can someone explain how this works with the magic number and the era's?

(As a small side question, why is it actually called the Alonzo era, while we're in the Cardano Goguen era? For the first two, they use the same era names, for the one we're in now, it's another name. It's a bit confusing.)

Answer 1

The network magic is not supposed to be mutable. The only reason it's in the Shelley Genesis is because the Shelley Genesis simplified the Byron genesis file format significantly and allows the code to "ignore" the mess of the Byron genesis file as soon as it reaches the Shelley era. Newer era Genesis files are additive to the Shelley era rather than a replacement like we had from Byron to Shelley transition.