What makes solutions like NAT* and IPv6 necessary is the concept of the "backbone". In spite of all its benefits, it also has tradeoffs too. When everything h

What makes solutions like NAT* and IPv6 necessary is the concept of the "backbone". In spite of all its benefits, it also has tradeoffs too. When everything has to pass through centralised "core" routers for enormous segments of the network, it limits how we can work with addresses. It forces us to allocate addresses in blocks (the larger ones within which most of the individual addresses remain unused). And it creates problematically large routing tables for those "core' routers. As with everything, there are both costs and benefits to doing things this way. There are always tradeoffs with any approach, whether it is centralised or decentralised. So arguments can go on to infinity about the "best" way. There is no such thing. There are just different alternatives, each with their own costs and benefits. And there's human consensus. And there are the inevitable workarounds, some of them pure "hacks". NAT* and IPv6 are a natural result of having a "backbone", "core routers", gigantic ever-growing routing tables and large address allocation minimums.