Because MAC addresses are only usable across the local network segment, we use IP addresses to communicate with other segments via routers. Meanwhile, for local targets, ARP is used to translate IPs into MAC addresses and the MAC addresses are used from then on in the conversation.
This leaves me to wonder why we use IP addresses at all on the local network. Given a scenario where all systems are in the same subnet, it would seem that IP addresses are then superfluous since the systems are only really using MAC addresses to route communications between each other.
Could computers actually do without IP addresses entirely, if they do not need to communicate outside the local network segment? Why don't they?
Best Answer
IP addresses are explicitly not designed to be bound by hardware where as MAC addresses are. MAC addresses can be changed temporarily most of the time but each device is supposed to have a globally unique factory assigned MAC address.
Furthermore, MAC is specific to Ethernet, and while it is now the defacto Layer 2 encapsulation method, it wasn't always the case and you never know if something better will come along in the future.