title: Why is it not possible to fake an IP address?
body: <p>I know it's possible to change an IP address using a proxy, but I'm interested in why is it not possible to change it by sending changed data from a single computer?</p>
  
  <p><strong>Update:</strong></p>
  
  <p>Thanks for quick replies, but it's not clear, what would happen, should a stateless protocol be used, like HTTP. I'm not familiar with lower-level network communication, but it seems that theoretically it should be possible to faken IP address if a PC connects to the server and receives the reply immediately.</p>