How to determine the local IP address a client behind a router?

[thesleepylizard]

At work I'm behind a router. That means when our remote web server handles an ASP.NET request, it looks like it's from ther router's IP address.

Say I need to determine the IP address of the actual requester, not the router. Or something that securely identifies them (IP address, MAC address, etc).

I've tried each of the ServerVariables but they don't seem to help. Any ideas?

(Obviously there's SOMETHING that identifies the client, since the router has to forward it back when it gets the response.)

 

[thesleepylizard]

For the record I've found an alternative solution which is quite complex, but does the job. Involves the server sending a random identifier number on each response (all responses are encrypted) and the cilent provides that on the next request to identify itself.

Much more complex than that, but that's the basic idea.

 

[stevexff]

Isn't that usually called a cookie?