Binding a user to an IP address?

Question

Mobile development

Hello.
The question of a binding of the user to IP addresses ipv4/ipv6 interests.
What is it for? There is a small web application and clients to it (web and mobile). Binding a user to an IP address/browser is needed to generate a key that will be used for further interaction with the server API.
Accordingly, several questions arose specifically on IPv6:
1) Can a mobile device (Android / iOS) simultaneously have two IPv4 / IPv6 addresses?
2) If both IPv4 and IPv6 addresses are available to the user, which one will be used by default?
3) How to determine which IP version is used on a mobile device?
Thanks

Answer 1

1. Maybe more. Depends on the number of interfaces (do not forget that in addition to physical interfaces there are also virtual ones in the case of VPN)
2. Depends on the interface settings. Other things being equal, one of the interfaces should always take precedence. Plus routing.
3. For example myip.ru, if you are interested in an external IP, or look at the interface settings - it is displayed there.
PS Binding by IP is usually additional security.

Answer 2

IMHO a hopeless undertaking. I now have a green dot at home, so it
's not possible to work via ssh through it. Once every 3-5 minutes, the session breaks.
A static IP is not given.
Mobile clients all sit from a small pool of ip addresses.
Have you ever seen how Yandex or Google begin to require captcha?
Session binding if done, then on a subnet.
And limit the number of requests per unit of time per key.