TPLink Deco Mesh setup, which Passthrough mode option?

DCHPS-Dynamic

Means that the first device to ask for an IP address via DHCP will be setup as the IP Passthrough device.  This is okay if you are sure that only your router can connect.  If you may want to connect with your phone or some other device, then this is a bad idea.

DCHPS-Fixed

Means that you specify the device that you want to be the IP Passthrough device from the Drop Down List.  The Gateway remembers its MAC address and any time that MAC address asks for an IP address, it will be treated as the IP Passthrough device.

Manual

Means that you will statically assign the WAN IP address, proper Default Gateway and Subnet mask to the WAN interface of your router so that it doesn't have to ask the Gateway for it.  The Gateway will just assume that you've done that and treat it as the IP Passthrough device.  This can be real useful if your router doesn't work with the Gateway's DHCP server well (some don't).  It can be a pain in the rare instance that your public dynamic IP address actually changes (which is nearly, but not quite, never).

I always choose Fixed, that way you're sure the BGW320 will always hand the public address to your Deco router.

Awesome, thanks! Sounds like fixed it is. That also would explain the dropdown list. Appreciate the quick help!

I used fixed until I had some unexplained dropouts that happened with a frequency pretty close to my IP Passthrough DHCP renewal period.  Then I went manual.  Loved it until I switched to fiber and got a new IP address and needed to manually reset the WAN and Default Gateway.  But that's the only time in years that my public dynamic has changed.

The passthrough mode you choose will depend on the configuration of your network and the requirements of your devices.

• DCHP-Dynamic: This mode will automatically assign IP addresses to devices connected to your network. This is the most common mode used for home networks, and it is the easiest to set up.
• DCHP-Fixed: This mode will assign fixed IP addresses to specific devices based on their MAC addresses. This is useful if you want to ensure that specific devices always have the same IP address, such as for port forwarding or other advanced configurations.
• Manual: This mode will allow you to manually configure the IP addresses and other network settings for each device. This is typically used for advanced network configurations and may require more technical knowledge.

For your case, you should choose DCHP-Dynamic as this is the most common and easiest to set up mode. It will allow you to connect all your devices to the network and have them automatically assigned IP addresses.

You should also check the Router's documentation, to confirm the setup process, and check if there are any specific settings that need to be done.

Additionally, you should check if there are any settings on the AT&T BGW320-500 gateway hardware, that need to be configured in order to work with the TP-Link Deco XE75 Pro.

@Ramoss Your advice is general, not specific to IP Passthrough, and as such really doesn't belong here.  I'm leaving it for now with this caveat.