How to get the Client-IP, even if a Proxy / VPN is used?

How do I get the clientIP from users in my regisrtationforms? It's easy to get the IP with the user isn't using a Proxy, Proxycacade or VPN. But if he uses one of those its difficult. X-Fowarded-For isn't reliable and fails within cascads.

But there are possibilities, because JavaApplets and Flash aren't using the Proxy-Services. How can I archieve to get the clientIP with those technics? I prever to use a small Flash-Code to get the IP from the client, but how to implement? Another way should be a counterpixel which is using IPv6. Most of the proxyservices only support IPv开发者_运维技巧4, can I tell an image only to use IPv6?

Maybe there are better solutions for my problem, so I look forward to you suggestions. Cheers.

Why do you want to know the IP address of the client? If they hide it then it's probably none of your business.

If you want to use it for limiting the number of connections, votes, etc. then think again. IPv4 addresses are running out so one IPv4 address will be used by many users, and even the IPv4 addresses between the ISP and the user and the IPv4 addresses inside a user's network will overlap. You will see the following situation more and more: You get a connection from a 'normal' IPv4 address, say 192.0.2.42. That will be a NAT box with i.e. 10.0.0.0/8 on the inside. On one of those addresses the user will connect a NAT box which NATs it to 192.168.1.0/24. Neither 192.0.2.42, the address in 10.0.0.0/8 nor the address in 192.168.1.0/24 will identify a user.

With IPv6 a user has an almost unlimited amount of IP addresses. An IPv6 address can only be used to see which /64 network the connection comes from, but not for tracking users or devices.

Giving meaning to IP addresses is pointless, unless you can go to law enforcement and get the NAT logs of all boxes involved...