How a Proxy Changes Your Exit IP Without IP Spoofing

“Spoof my IP” is often used casually to mean “make a website see another address.” A forward proxy can do the second thing without doing the first.

In the ordinary explicit-proxy arrangement, your computer connects to the proxy using its real network route. The proxy opens another connection to the destination. The destination receives that connection from the proxy's outbound address, or from the NAT device in front of it.

Your application -- connection A -- proxy -- connection B -- website

Connection A and connection B are not one TCP connection with an address label painted over. They have their own transport state. The proxy may relay the same application bytes while the surrounding TCP segments, acknowledgment timing, and packet boundaries differ.

Why the return traffic still works

The website replies along connection B. The proxy receives those replies and carries the relevant data back along connection A. Both legs have a participant able to receive traffic at the address it uses.

Forging a packet's source address is a different operation. It changes where a receiver would send its response. Ordinary TCP connection setup depends on receiving the handshake responses; merely writing somebody else's address into an outgoing packet does not provide a usable web session at that address. The TCP specification defines that connection establishment.

One visible address is not the whole identity story

The website can still receive account credentials, cookies, or forwarding information. The proxy still receives the client's connection. Those facts do not turn the operation into source-address spoofing; they explain why changing the destination's observed network peer is narrower than making the entire interaction anonymous.

For troubleshooting, ask which connection and which observer produced an address. “My IP changed” is useful only after identifying where it was observed.