Bridged mode means the DSL/Broadband modem/gateway device only terminates a DSL connection.
About Bridge Mode with AT&T
In a bridged mode, the modem/gateway device does not authenticate, does not manage, has no ability to perform any firewall protection, and does not allow for remote access into the modem/gateway device. The subsequent device connected to the DSL/Broadband modem/gateway device has to perform all these tasks, if needed.
Bridged mode is not possible on the AT&T platform. The reasons for that are:
Bridged mode is not compatible with AT&T services, because AT&T requires all gateways to have 802.1x proprietary authentication.
AT&T Customer Care has no way to remotely access the modem/gateway device in order to do diagnostics testing.
A bridged mode configuration does not allow the device to receive any future firmware updates from AT&T as remote access is disabled with a bridged mode setting.
PPPoE is not applicable on the AT&T platform.
If you are trying to enable Bridge mode because you have a third party router that you want to manage your network, or if you have another device that you want to receive a WAN IP address, several configuration options are available. Please visit Configuring Ip Passthrough and DMZ plus for assistance configuring your hardware.