Either you store it in a cookie which the browser passes to the server for you, or you store it in a url parameter and you (or your html / temp laying Generation framework, or some JavaScript manipulation) needs to ensure all links or other server calls like POST, will need to include that session ID passed back to the server.
And this talk about IP addresses is complete nonsense because of Proxies and NAT and a ton of other reasons. You can attempt to use it in combination with a session ID, but you certainly cannot use that alone.