so if I send a packet from a host to another from the same network we know the mac address of both the source and destination.
However if the receiver is in a remote network the destination mac address will be first the router's mac then changed to the actual destination (let's assume there's one router connecting the networks).
My Question is: if the final mac address is not mentioned in the initial packet (but instead replaced with the router), how does the router know it?
Now I know there's the arp protocol that translate the IP address into a mac address, but from my understanding the mac address is associated with the nic and I think that a single device can have multiple nics and thus multiple mac addresses, so how does it choose the correct one? unless each nic is connected to a different network, and in that case what's even the use of a mac address?