Thank you very much. But I have read hours of documentation like this. And each solution is saying to "refer to the product documentation or manufacturer's website", that is really hard to understand when you are not a technicien. For me it's very complicated to understand. I forgot to say the dap-1360 is plug into a cable modem. When the cable modem is pluged directly into the iMac, everything works perfectly and I have access to the internet. But when it is plug into the dap-1360, the iMac can see the dap-1360 but don't give me access to the internet.
So if somebody has already something similar that is working, I would like to know what ip adresses (ipv4, router address, etc.) to put on airport on the iMac, and how I can set the dap-1360 so it can let me access the internet.
Thank you.