Why though? You can't route MAC because... ?
Because ipv4 provides a higher entropy address?
Because MAC is self-assigned and reduplication would require a higher level system?
or just because we just don't use MAC addresses that way?
I'm certain there are reasons IP came to live alongside/on top of MAC, but saying you can't do multi-hop routing with it just isn't true. If all the technologies of the Internet were reset tomorrow, how might you design the perfect layer 2 addressing and routing system?
MACS are random. Given a MAC and a connection to a LAN, you can easily answer the question, "is there a station with that MAC here". If it's not here, and you have a single gateway to another network, you can figure out that to talk to that MAC, you need to go over a gateway. And then things eventually go funny. We hit a network that talks to four others. It has no idea where to send the packet destined for that MAC. It could send it to all four (multicast). Then when a reply comes from one of them, remember that destination for next time. Remember for how long? Sending a packet to every destination will cause an exponential explosion of that packet throughout the network.
It works on small scales. We can stitch together a few LANs with ethernet switches. The switches initially forward everything to all ports, but learn where the MACs are so as to send frames only to ports where the destination MAC is known to be.
Ethernet switching won't scale to anywhere near the complexity of the Internet.
You can't route MAC because there is no prefix matching - only exact matching. That's exactly why you need to "switch" them... and incidentally this is what your proposal accomplishes – it's equivalent to a fully-switched network. Switches (especially L3 switches) maintain port-MAC association tables to switch packets between ports and they're available off the shelf.
IP addresses have structure because a single ISP buys a contiguous block, like 123.234.*.*. A simple routing table sends that whole block to a single network port.
The table required for the whole Internet is large, but not gigabytes.
You can't route by MAC-address because it's effectively random. You'd have to store the port number for every device separately. This works fine at LAN scale, but not for the whole Internet.
MAC addresses being random is a historical accident (because of hardware limitations). today we can define them in software. and just like we have link-local addresses we could self-assign link-local MAC addresses.
and i think the self assigning protocol in link-local could even go a step further. instead of hard coding a subnet, it could detect the subnet by copying the one from its nearest neighbor. so start with a random address, talk to neighbor to learn the subnet (and netmask) in use and switch to a new address within that subnet. then possibly run DHCP and update the address again. for static addresses DHCP could identify hosts by its cryptographic host key (like the one for SSH)
when two subnets join one of them may have to adjust its prefix. more complex, but still possible.
subnet prefixes could still be assigned to organizations to avoid overlap on a global level.
i am sure i am missing some details but i think in general this could work.
well, it's merging MAC and IP into one address. there is no need for two if the MAC address can be assigned dynamically. and it's extending the auto-discovery of the address to work over larger networks. so it's not reinventing but simplifying things. (or not, i am not familiar enough with the details to be aware of other problems that could complicate things again)
>You can't route by MAC-address because it's effectively random. You'd have to store the port number for every device separately. This works fine at LAN scale, but not for the whole Internet.
Not that I see any advantages to the approach but it's almost workable(?), if a little silly, at internet scale:
If every device had a 64byte ID, guesstimating 10billion people * 100 devices/head gets us a 'measly' 64TB of storage. Double that to include routing info gets us to ~128TB. A bit much to be practical, but not entirely insane either.
the router needs to remember where each address goes. with MAC addresses being random, there is no shortcut. DNS is distributed and you look it up one subdomain level at a time, and that can be cached. same for IP, the router only needs to store the subnet for each destination, not all ip addresses.
a central lookup database for mac addresses (which could be distributed by having separate servers for a segment of the address space) doesn't make much sense because the distance of a server to the location of the device is to great and would make updates expensive.
so the router has to remember each address used. but at least it would not have to store all addresses in existence. actually, i think the storage needs are similar to those for NAT. well, except backbone routers which have to store a lot more.
the actual problem is the initial discovery of a MAC address. where does the routing information for a MAC address come from?
you need some peer finding protocols like DHT, and those are slower.
Because aggregation, summarization and continents are a thing. Also... there are things which speak IP and don't use Ethernet for underlying communications, specifically in the network carrier and high performance optical space.
I used a MAC address generator to get those two, but I think two is enough to make the discussion. Current reality aside, would you be able to identify those with binary math as being on the same network device, different network devices, across the world? MAC addresses on physical NICs are provided by the manufacturer, sure you can adjust them but I think that leaves the good-faith portion of this discussion.
So if you wanted to have those to communicate no matter what you would have to have a network device state: "I'm network device A, I have this device 0C:F9:31:D2:DB:51" then another state: "I'm network device B, I have this device AB:33:C6:C6:19:74". Then whenever 0C:F9:31:D2:DB:51 wants to talk with AB:33:C6:C6:19:74 it's network device will have to just send it to the next upstream network device or if there are multiple network devices that could be upstream you could send it to them all which is just not great for security whatsoever or you now have to do a recursive lookup for whatever n devices might yet be upstream and wait for a response to see if one of those has it. Overall trying to send ethernet frames globally without an IP network sounds like not a great idea.
So it seems like the primary use of IP, as you describe, is to define a way to narrow the search to sub address groups so as to not require enumerating every address in the scheme.
Still, there's doesn't seem to be any reason you couldn't just say "device 1 gets MAC 00:00:00:00:00:01" and "device 2 gets 00:00:00:00:00:02" and the gateway controller gets :::00 and there's a special address on :::FF that can be used to talk to everyone...
Is that it? Is that all there is to IP? A loose pattern for reducing search scope, a couple reserved addresses for special cases, and a balance between address bitsize and total number of unique addresses (without requiring additional routing complexity)?
You could. Assuming all your equipment supports setting the MAC, and you make sure to operate on prefixes so you can route by prefix. There's nothing stopping you from doing so.
The reason we don't is because at the time IP was introduced, there were many alternative physical layers in active use. And while Ethernet is near ubiquitous now, what we learnt from that was that it is unreasonable to assume that all your data will go over the same physical layer. And so you need a standard addressing format that will work elsewhere too.
Nothing stops you from stripping it back locally and using MAC addresses for everything internal to you, and ditching IP, and "just" gateway to/from IP. Lots of people did gateway between different protocols before IP became the dominant choice.
But you won't get everyone else to change because it'd require new firewall and new routers, and all kinds of software rewrites, and you can see how long the IPv6 transition has taken, so you'd still need to wrap and unwrap TCP/IP and find a way to address IP for everything that isn't 100% local, and even for lots of local-only stuff unless you want to rewrite everything.
There would be potential ways. E.g. you could certainly use a few bits to say "this is external" and then have some convention to pack an IPv4 address into the MAC or let an IPv6 address overflow into the data, and use that to make gatewaying and routing to external networks easier, while everything else just relies on the MAC. But you'd still need a protocol header for other things too, and then the question is how much benefit you would gain from ditching pretty much just ARP, which isn't exactly complex, a lookup table, and replacing the IPs in the header with just a destination MAC. Because the rest of the complexity is still there.
And you can gain most of the benefit of that by getting an IPv6 EUI64 address [1]. They'll work with "normal" IP equipment, and you can optimize in your own software by having the IP stack ditch ARP lookups when they see a local EUI64 address. Whether that optimisation actually makes a difference is another question.
Then you realize doing some action ends up being O(n^2) so you add some workaround in your switch and cache some things. And you know what they say about cache invalidation. And vendor A implemented it wrong in 1993 so you have a special case for their systems. And then you want to handle abuse cases. And authentication. And you're competing against the whole rest of the world and your thing isn't enough better.
Then how do you send traffic to device1 on another network? You need globally unique addresses and hierarchy. Go back to the drawing board and come back when you’ve ended up inventing a worse IP protocol.
> It all seems so... simple
Because you haven’t even thought through basic use cases.
MAC is just one way to identify ("address") directly connected/visible nodes on a network. Not all L2 technologies use MAC addresses.
- "Directly connected/visibile" means node X can contact node Y simply by throwing something on the medium (wire, radio, etc.) and doesn't have to knowingly send to a middleman (router).
When Ethernet was invented in the early 80's there were a lot more L2 technologies. Most are uncommon now (Frame Link DLCIs I think fall in this category, and PPP/dialup was common at one time - no MACs there) except for one: I don't think the cellular network uses MAC addresses at all. I could be wrong with newer 4G/5G stuff which overlaps with Wi-Fi in various places.
> I'm certain there are reasons IP came to live alongside/on top of MAC
There were different teams/universities working on what today we would call LAN and WAN. I forget the details and history (I'm sure someone here, who was involved, could chime in, hah) and might have this wrong, but the result is LAN networking is MAC based while WAN networking is IP based.
It's one of those accidents of history that things are just the way they are and many don't question it. I run into it a lot describing basic networking concepts or early cisco material when people ask _why_ both MACs and IP addresses exist and its just... not always the correct time to explain those details to them.
I'm certain there are reasons IP came to live alongside/on top of MAC, but saying you can't do multi-hop routing with it just isn't true. If all the technologies of the Internet were reset tomorrow, how might you design the perfect layer 2 addressing and routing system?