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I’m having a hard time thinking of what kind of network topology would result in a routing loop. Can you elaborate? It seems like the first router would have

by comex 5y ago

I’m having a hard time thinking of what kind of network topology would result in a routing loop. Can you elaborate? It seems like the first router would have to be forwarding only a subset of a /32 to the second router; if the second router was responsible for the whole /32 (or more), then it would have no reason to send packets back to the first router even if it didn’t know about the extension. But forwarding a subset of a /32 to a router that doesn’t know about the extension is clearly a misconfiguration.

lmm 5y ago
Two different /48s might be on two different sides of the world; the first router has no idea what the full path from it to either of them is (and of course the path shifts dynamically because that's how internet routing works) so it has no idea which paths might have IPv4-only routers on. If you have to advocate addresses in IPv4-routable blocks (/32s, or I think /30s in practice because of needing a broadcast address etc.) then your protocol doesn't fix the address exhaustion problem and you still have to make a clear distinction between the parts of your network that are running "v4.1" and the parts that are running "v4". You'd end up with something like 6to4/6rd but running that way forever, with no prospect of ever improving, and the IPv4 address space fragmentation issues would get worse and worse. So there's not really any practical advantage over CGNAT.