IPv4 forwarding connects two / more networks by sending packets which arrive on one interface to another interface. It makes it works as a router. For an instance, can connect home network with the internet by IP forwarding. Typically in windows computers, it is there as:
HKEY_LOCAL_MACHINE \SYSTEM\CurrentControlSet\Services\Tcpip\Parameters and by modifying “IPEnableRouter”. Or Control Panel > Network > Protocols > TcpIP Protocol….