The world in which IPv6 was a good design (2017)
&gt; Edit 2017-08-16: It turns out that nothing in this section requires IPv6. It would work fine with IPv4 and NAT, even roaming across multiple NATs.<p>That&#x27;s not quite fair. IPv4 and NAT require maintaining a lot of state at critical intermediate routers. I&#x27;m sure we&#x27;ve all experienced (perhaps regularly) a NAT&#x27;ing router losing state because of a reboot, state tables overflowing, or similar hiccups.<p>The one absolutely redeeming quality of IPv6 is that with 128 bits routing can be kept much more hierarchical and stateless. Fragmentation will occur and is occurring because we now apply trust metrics to IP addresses (thanks, spammers!) so there&#x27;s value in owning transferable subnets, but I think IANA and major ISPs can keep the fragmentation process slow enough that hardware&#x2F;software capabilities can stay apace, preserving a largely stateless, hierarchical routing infrastructure.<p>That doesn&#x27;t solve the mobility problem, but it does provide significant benefits to mobility solutions. Don&#x27;t underestimate the cost of NAT&#x27;ing in terms of systems complexity. NAT&#x27;ing isn&#x27;t the type of layer, like ethernet MAC addressing, that we&#x27;ll always be stuck with.<p>It&#x27;s also worth pointing out that some of the [now] unnecessary complexity of IPv6 will fall away over time. IPv6 will get simpler as time progresses, as it already has.