Can a Time Capsule in bridge mode assign static ip addresses

No, a bridged TC is basically a glorified switch/wifi AP/hard drive.

There are ways of doing what you want though.. the AT&T router should be able to do it.. since it is currently assigning IP via DHCP.. just check what the main router can do.

There is another mode other than bridge and router for the TC.. that is DHCP.. It is tricky to setup but I can give details if your main router has issues.

The "Off (Bridge Mode)" setting means that the routing functions of the Time Capsule are turned Off, so it cannot act as a router to distribute IP addresses in this setting. As it stands, the Time Capsule is simply passing through the IP address information to connected devices that is being handled by your ATT router.

As LaPastenague mentions, if you need to assign one or more static IP addresses to devices on your network, you'll need to check the settings on the ATT router. Usually, you do this by entering the default IP address of the router......something like 192.168.0.1 for example......into your browser and then entering the password for the router.

This information is usually found on a label on the bottom or back of the router. Check with ATT Support if you need more information about setting up your ATT router to provide static IP addresses.