IPv6 comes with a slew of improvements from larger address space to self-organizing addressing to required support of multicast, but these improvements are a double-edged sword. With NAT going away, DHCP no longer being required, modern operating systems and networks supporting and preferring IPv6 over IPv4, ICMP being required for network operation, iptables not applying to IPv6, and multiple IP addresses being associated with individual interfaces, IPv666 conjures the perfect storm of fail open defaults.