Hacker News Reader

Comment by noahl | Hacker News Reader

This was a very informative article for me, but there was one thing I didn't understand. At the end he made the case that mobile routing needed essentially two layers: a fixed per-device (or per session) identifier, and then a separate routing-layer address that could change as a device moved. QUIC has session identifiers, and that's great and could solve the problem.

But earlier in that very article, he already pointed out that every device already has a globally unique identifier used in layer 2 routing ... the ethernet MAC address.

Would someone please explain to me why we can't use MAC addresses as globally unique device IDs?

(Is MAC spoofing the issue?)

View on HN

In theory we can use MAC addresses, but there are problems: 0) Privacy: You don't want all traffic to be labeled with your hardware ID. 1) Flatness: MACs are essentially random, and a router would need a huge table to keep track of who's where. IP (v4/v6) assigns addresses hierarchically, making routing tables manageable.

The idea would be to use IP addresses for all levels of routing, and MAC addresses only on the endpoints to identify the connection. So routing actually becomes simpler. However, you have a good point about privacy. One of the other commenters also mentioned non-unique MACs.

Another point against using MACs which I want to point out is that they don't make much sense if you have a service running on multiple hosts. I mean, you could introduce "virtual MACs", but it seems better to keep the idea of "service ID" separate from "device ID". Session IDs solve the multiple hosts problem too, by completely avoiding it.

I think, he explains it early in the article,

"The problem with ethernet addresses is they're assigned sequentially at the factory, so they can't be hierarchical. That means the "bridging table" is not as nice as a modern IP routing table, which can talk about the route for a whole subnet at a time."

MACs aren't unique and can be changed. Certain fly by night Asian manufacturers just make up MACs randomly. It's a big problem with counterfeit gear, too.

They are supposed to be unique, but in the real world they are not.

Among other reasons: there are still a fair number of non-Ethernet devices with IP addresses out there...

Reply on news.ycombinator.com