So I see that GT4 is a special case , not just default net config , you should dedicate a net config for it , from it
EDIT: Wow . Just enable Use DHCP in the configurator
Primary DNS will be 192.168.0.1 (should it matter)
Finally run kaiEngine.exe I guess making private arena in the GT4 arena can help
The host may go to waiting for connection screen first , did this numerous times
In the GT4 options Host Yes Players 2 Traffic Light , head to LAN>waiting for connection screen then tell your buddy to head there too , the menu should proceed then must not press anything
PROFIT =} I even got to host for two others who were far far