Why is it not possible to fake an IP address?

Question

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?

Answer 1

If you try to send a packet by changing the source ip addres you can send it to someone else but if you want a packet to return to your pc you must use something like a NAT

If you are behind a router on your network you are in essence changing hiding your own identity

Example: you : 192.168.1.4 insiderouter: 192.168.1.1 external-ip: 8.8.8.8 destination-ip: 8.8.4.4

Sending a packet: from: 192.168.1.4 (you) to 8.8.4.4 (dest) router transelates to : from: 8.8.8.8 (external-ip) to 8.8.4.4 (dest) and keeps your ip in his memory

than the packet arives at his destination.

Now the destination sends a packet back from: 8.8.4.4 (dest) to 8.8.8.8 (external-ip) router transelates to (whith using its memory) from: 8.8.4.4 (dest) to 192.168.1.4 (you)

and now the packet returns to your pc

as you can see the destination doesnt know your ip but only knows the ip of the router

this is a way you can acclompisch a way to hide your ip