Why not use MAC addresses instead of Local IPs?

Question

In similar questions, the question that has been answered is:

why do we need both MAC and IP addresses on the internet? They are both addresses. Why can't one just be used to describe a device?

The answer is along the lines of:

The two protocols are not universal, not all devices use it. IP provides a logical address and allows routing, MAC doesn't support routing, and more.

My new question is:

That's a nice answer as to why the internet as a whole needs both types of addresses, but why do we need Local IP addresses?

Locally, on the same network, no routing is involved, I'm simply sending to the computer next to me. Why can't I just send directly to his MAC address? And the router that connects our local network to the internet - why can't he just store a table of MAC addresses to keep track of what from the outside world goes where in the "local world"?

The existence of Local IP seems unnecessary.

Answer 1

So lets forget for a second that all modern OS's are primarily based on IP/IPv6 and your suggestion would completely break everything. Imagine this analogy:

An IP address is like a fully qualified postal address:

I. M. Ray
1024 Megabit Dr
Somecity, State 10101

Your MAC address is your physical house. The blue one 4 house from the corner, with the big oak tree.

When someone is sending you a letter conventionally, the mail is routed to your local post office based on the full address. We will compare this with routing of IP over the internet. The post office the mail was sent from could care less about your oak tree.

In the conventional method, the post man would organize his deliveries by street, and go house to house delivering the mail. This is similar to ARP table, we have organized the houses into an easy to find and navigate index.

In your proposed method, as soon as the mail arrives at the post office, they replace the envelope with your full address to one with a description of your house on it. It is now the post mans job to remember where the Blue house with the oak tree is.

So, while your thoughts are on the right track, they are just not practical. Once you are on the same layer 2 domain (local), then you don't necessarily need routing and could in theory use just physical addresses.

I am sorry if this is a pretty far out answer. I've been reading your other questions on the topic, and it seems as though you are trying to wrap your head around this subject, and this was my best attempt at breaking it down logically. The whole idea is pretty tricky to understand at first (we've all been there), but once you figure out the parts and the role they play in the grand scheme, the more it starts to make sense.

Please feel free to ask if you have any questions, as my primary intention of posting this is to actually help you out.