I'm using Ruby on Rails as server-side framework, but I'm sure that solution is cross-platform.
I want to show user his real ip address. The application is deployed in corporate network. Most of users connect to application in straightforward way without proxy, NAT and etc. But some of them use proxy.
Now they see IP address of proxy server.
What is the best way to show them their real IP address?
As I could see It is not possible using only serve-side techniques. So solution should be something using JS (almost all users enable JS), Flash (about 80% users use it) or JAVA (about 50%). It would be great if solution was rails plugin, but it is not so important.
UPD. Unfortunately, X-Forwarded-For header has no interesting information.
UPD2. I want to show a local network ip (e.g. 192.168..).
UPD3. Almost all client browsers are Internet Explorer (7,8,6 versions)