NAT (Network Address Translation)

Network Address Translation lets a whole private network reach the internet through one public IP. Your router keeps a table mapping internal, private addresses to the single public address, rewriting the address fields of packets as they pass in and out. NAT exists because public IPv4 addresses are scarce; it also incidentally hides internal devices, since the outside world sees only the router's public address. Almost every home and office network uses it, which is why many devices can browse at once through one connection.

When an internal device sends a packet out, the router replaces its private source address with the public one and notes the mapping so it can route the reply back to the right device. Unsolicited inbound connections have no such mapping, so NAT blocks them by default — which is why exposing a service requires explicit port forwarding. Because outsiders only ever see the router's public address, NAT provides a basic layer of obscurity, though it is not a substitute for a firewall or for the origin-masking a VPN or proxy provides.

s4m has selectable public exit configurations. Use the endpoint or profile issued for the protocol and location selected in your account. An outbound exit address does not by itself open inbound ports to your device. That requires separate supported routing and firewall configuration. An exit IP can have a prior history. Accounts, cookies and browser signals may still identify a user; changing an address does not guarantee a clean reputation. Related topics: origin IP, VPN, proxy, exit IP, CGNAT, dedicated IP.