Bridge mode means that the "modem" doesn't do any Level 3 processing on the traffic and passes it through, sort of like an Ethernet switch, e.g. you wouldn't see a HOP in traceroute. With the AT&T Gateway you cannot achieve a true bridge mode. The best you can do is:
For a static public subnet: the Cascaded Router (if you want to use a router to manage the public subnet)
For the dynamic public subnet: IP Passthrough (or DMZplus on the Gateways that call the feature by that name).
For a static public subnet: the Cascaded Router (if you want to use a router to manage the public subnet)
For the dynamic public subnet: IP Passthrough (or DMZplus on the Gateways that call the feature by that name).
When configured for IP Passthrough (Passthrough Mode) the AT&T provided gateway shares its Dynamic WAN IP address with a single device on the LAN.
