I am unable to connect to certain online games at the same time and in the same game session as another user in the house. We’re both connected to the modem via ethernet cables. It appears that these games (so far it’s Call of Duty: Modern Warfare 2 and Call of Duty: Black Ops) seem to be unable to tell the difference between our two computers so one of us gets booted. However, if I connect my internet using a different manufacture of modem, I have no problem. I’ve also tried connecting up with an old Draytek 2600G modem and everything worked fine, we were able to join the same matches. I’ve tried a number of different NAT settings and tried forwarding ports for one of the computers only as well as for both and for none (the other modems tested worked fine without having to forward ports at all).
The “Call of Duty” game requires a number of ports as listed at:
20500, 20510, 28960
ADD the All TCP and UDP ports to NAT >> Open Ports.