IPv6 is not a "wildly different network stack". It retains almost everything of the IPv4 stack. It replaces some small parts of the stack (e.g., DHCP by statele

IPv6 is not a "wildly different network stack". It retains almost everything of the IPv4 stack. It replaces some small parts of the stack (e.g., DHCP by stateless auto-configuration, which doesn't affect applications). Updating an application-layer IPv4 program to support IPv6 is usually just a matter of fixing the structs/API calls. And how is it "much more complicated"? IPv4 with layers of NAT bolted on top of it in an ad-hoc fashion doesn't strike me as a paragon of simplicity. The IPv6 world seems much cleaner to me. Also, IPv4 addresses absolutely are complicated enough to have warranted their own Wikipedia articles: https://en.wikipedia.org/wiki/Classful_network https://en.wikipedia.org/wiki/Classful_network, https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing. But it doesn't matter - for the most part, applications don't need to care about the structure of an IPv6 address.