Unable to play games together on the same network

I have purchased genuine copies of games like Black ops, Arma 2, Dayz, BF3 and BF4 for my Sony Vaio Z Series.
When me and my friend wanted to play together being on the same server, it is not allowing us. But when we play separately, we are able to do so. None of the games we own, allowing us both at the same time. We both are using the same network using separate Ethernet cables.
What is the cause of this issue? Is there any setting I have not done to allow more than one person to play the game?
