For my web application I want to increase the security a bit by checking the route that a visitor has made to get at my server. Now, there is various information already available on how to do a traceroute where you'd just generate an outgoing request for the IP address. (This SO answer, for example.) But I don't want that!
What I want is that I get an incoming request and I want to know the route that this specific request has taken! I don't want the route to the visitor but the route of the request. And I'm not sure if this information can even be retrieved in some way...
Is this possible? If so, how? In C#, of course...
Short answer: "NO" See RFC791
The request may have been fragmented, different packets taking different routes to reach you, and the return path may well be different. That's the beauty of IP and without it the packet would grow in size as it traversed the network.