Every device comes with default settings. You get the details about those settings in manual. Since they’re common for every device of the same model, it is advised that you change them for security reasons. In order to know, AT&T router access code. Go to the gateway settings. There is a system information tab there, click on that and enter your current code. You will find the default code on the side. It is usually 192.168.1.1 or 192.168.0.1.