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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.

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CodyBugstein
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1 Answers1

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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.

David Houde
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    Another thing worth mentioning is IPv6's Link-Local addresses. These are IP addresses automatically generated by the network interface without the need for configuration. This doesn't answer your question, but does allow local communication without the need for assigning IP addresses or relying on a DHCP server to assign an address. It might be interesting for you to research as it seems like it may help you understand their solution to a similar problem. – David Houde Jun 27 '14 at 09:17
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    First of all, thank you for your generous answer and being a good sport about it. I've encountered a lot of downvotes simply for asking a question that was asked before in a different way and context. I really appreciate it! – CodyBugstein Jun 27 '14 at 09:45
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    Second, in your analogy, you say an IP address is like what's written on the envelope, and MAC address is like describing the house (4 from the corner, Oak tree, etc). So what would a Local IP be in this example? I guess it would be like a postman who numbers all the houses on his route, right? I still fail to see why this is better than using MAC addresses. What new capabilities does it add? – CodyBugstein Jun 27 '14 at 09:48
  • Local IP wouldn't be used by the post man, since no outside mail can be routed there. It's more like your neighbors all know you and what your house look like, and they can just come knock on your door if they need something, instead of having to get the government involved and have a certified mailbox installed and numbered. – David Houde Jun 27 '14 at 09:50
  • The capabilities are that it is auto configured among the local neighbors. There is no need to configure an IP or rely on DHCP to assign one. It is very similar to what you suggest as using MAC only, but the main advantage it has over using MAC only is that it WORKS. You cannot just avoid the TCP/IP stack and expect things to work. This is probably the closest to your idea that would actually work in the real world. I am sure it would be possible, but no one wants to redesign the internet – David Houde Jun 27 '14 at 09:52
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    "Local IP wouldn't be used by the post man" So back to my question, why do we need Local IPs, if the *post man* can just use MAC addresses? – CodyBugstein Jun 27 '14 at 11:44
  • It is not required, just very widely adopted. You could encapsulate anything in a Layer 2 frame with only the MAC address. You would just need to implement a different protocol or create your own, and it wouldn't work with the rest of the internet. – David Houde Jun 27 '14 at 11:50
  • Would you say the server to router and router to local computer are using the same protocol. Namely, the protocol to go from IP to IP? If so, I think Cody is asking if there is anything inherently wrong with using an IP to MAC address protocol for the router to local computer interactions. – Joshua Segal May 12 '20 at 19:30