USA - AT&T fiber - IP passthrough configuration [2026]

[Bill_Stewart]

As of Feb 2026 I am an AT&T subscriber and they provided a BGW320-505 as the gateway device. I already have a robust ASUS router set up with the features I want and I want to use the BGW320-505 as the gateway only.

Here's my working configuration for those who might be curious:

Home Network -> Subnets & DHCP:

• Device IPv4 Address: 192.168.1.254
• Subnet Mask: 255.255.255.0
• DHCP Server Enable: On
• DHCPv4 Start Address: 192.168.1.252
• DHCPv4 End Address: 192.168.1.253
• DHCP Lease: 0:0:10:0 <i.e., 10 minutes>
• Public Subnet Mode: Off
• Cascaded Router Enable: Off

Firewall -> Packet Filter:

• (Disable packet filtering)

Firewall -> IP Passthrough:

• Allocation Mode: Passthrough
• Passthrough Mode: DHCPS-fixed
• Passthrough Fixed MAC Address: <MAC address of router's WAN interface>
• Passthrough DHCP Lease: 0:0:10:0 <i.e., 10 minutes>

Firewall -> Firewall Advanced:

• (Disable all settings)

Random notes about the above:

• The DHCP server in the BGW320-505 must be enabled or you can't change Passthrough Mode to DHCPS-fixed
• The DHCPv4 start and end address specifies 2 addresses because the GUI requires at least 2 IPs in the range; changing this range is optional
• ASUS routers apparently use the same MAC address on the LAN and WAN interfaces; the Passthrough Fixed MAC Address in my configuration matches the MAC address on the router label
• I set both the DHCP Lease (Home Network -> Subnets & DHCP section) and Passthrough DHCP Lease (Firewall -> IP Passthrough section) to 10 minutes

Now I have seen the case where if the router reboots, its WAN interface can get assigned a private IP from the BGW320-505's DHCP server. After restarting the WAN interface on the router, it gets assigned the public IP. I'm still testing on how to prevent this from happening.

Hope this helps.