bon, impossible de copier le lien sur JV.com...
donc je te mets directement la réponse du support technique trouvée sur ACTIVISION
To setup for multiple users:
1) Right-click on the Play Call of Duty Multiplayer icon you use to start the game.
2) Select Properties.
3) In the Target field you´ll see a line like " C:\Program Files\Call of Duty\CodMP.exe", add the Quake III net_port command to specify a unique communication port for each system. The complete field should look like this:
" C:\Program Files\Call of Duty\CodMP.exe" +set net_port 28960
4) Click OK.
5) Repeat for each system behind the NAT, adding one to the net_port selected ( 28960,28961,28962)
While the first player behind the NAT joins fine, adding additional players is problematic in the default configuration. Symptoms include rejected challenges, invalid cdkey, dropped delta packets, and severe " connection interrupted" messages.
By default, Call of Duty clients send and receive data over the same port, causing the server to treat multiple clients as a single data connection.