IPv4 vs. IPv6 FAQ
My issue with IPv6 is that its designers assume that everyone with an IPv6 network will get static IPv6 addresses.However, it didn’t turn out that way in the real world.  Every time my router resets, all of the IPv6 addresses in my home network change.  So, I don’t use IPv6 to connect among computers in my home network; since I also get one IPv4 address from my ISP, I simply use IPv4 NAT so that the addresses in my home network are easily remembered and do not change.The reason I don’t use IPv6 and 6:6 NAT is because the IPv6 designers feel this makes networking too complicated, never mind that NAT is a solved problem, so 6:6 NAT support just really isn’t there.Another annoyance I have with IPv6 is that it needs to have more than one localhost IP address, considering that IPv4 has a 24-bit space for localhost.  A large number of localhost addresses is useful for network regression tests (e.g. if we have one authoritative DNS server on 127.10.0.1 and one which isn’t responding on 127.10.0.2, does our recursive DNS server on 127.12.0.1 correctly handle an upstream DNS server being down?  Nice to be able to run the test using only localhost IPs; also nice to be able to change the IPs each test so we don’t have to wait for the kernel to release TCP sockets for a given IP + port).For the record, I have gone to a lot of effort to give my open source networking software IPv6 support.