Right now, there is another battle between AT&T's CGNAT (entire customer base) and Yahoo's NEW login authentication mechanism.

Web browser visiting Yahoo Mail is poorly comparing your external IPv6 with your home's IPv4 and rejecting your login.

This problem gets worse for Linux users as more and more websites (DirecTV) start to use the NEWEST Yahoo login authentication until AT&T somehow starts disbursing IPv6 inside your LAN, ... or something.

So "NAT" security is technically being compromised by Yahoo's JavaScript.