alt Hacker News> We can't have globally routable, unique, random-esque ID precisely because it has to be hierarchical
This is not, technically, true. We could have globally-routable, unique, random-esque IDs if every routing device in the network had the capacity to store and switch on a full table of those IDs.
I'm not saying this is feasible, mind you, just that it's not impossible.
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I guess it depends on what you mean by "impossible." If you only mean that it's theoretically possible, then sure, one can imagine a world where that is done. But even with IPv4's meager 32 bits of address space, it would explode TCAM requirements on routers if routers would start accepting announcements of /32s instead of the /24s that are accepted now. And /64 (or, jesus, /128) for IPv6? That's impossible.
It isn't just storage - lookup in those tables needs to be usefully fast.