The IPv4 address may be a private one, with a NAT box between you and the web site. This is very common on cellular networks (because of the large number of dev

The IPv4 address may be a private one, with a NAT box between you and the web site. This is very common on cellular networks (because of the large number of devices), even in developing countries with good allotment of IPv4 addresses. They have to do large scale NAT (CGNAT = Carrier Grade NAT), and it can have a bad influence on performance. During peak time those boxes can become a bottleneck. Let's take an example I got from a Cisco presentation, when NAT is used. A map web application may have to download a lot of tiles quickly. It's best done using several parallel TCP connections. Each of those connections must be tracked by the NAT box. At scale and for peak time load, this can become a nightmare and some connections may be dropped --- leading to retries and delays in completing the web page display. With IPv6 this issue doesn't exist. Supporting IPv6 can help providing a better mobile user experience in this case, and is why a lot of the big companies do support IPv6 already. Bypassing CGNAT helps with latency in a situation as in the above example.