Setting up a third-party router with AT&T Gateway with IP Passthrough

About two weeks ago, I had bought a TP-Link router to use for my home network. The problem was… I have AT&T as my ISP Internet Service Provider - A company who sells you access to the internet . Despite the fact that many (including me) associate AT&T routers with being very restrictive, not allowing you to change many settings, this process was more or less surprisingly simple and straightforward. Here’s how I did it!

Note: This guide applies to the AT&T BGW320-500 fiber modem/router combo. You may have trouble following along if you use a different generation device.

What is IP Passthrough

IP Passthrough on AT&T Gateways is a feature that allows your Gateway to act as a tunnel, disabling its built-in firewall A security system that monitors and controls incoming and outgoing traffic on a network, blocking unauthorized access , and assigning its WAN (public) address to a single LAN device.¹

On the other hand, there is also DMZplus and Bridge mode, but I will not be discussing those as the BGW320-500 doesn’t support them AFAIK As Far As I Know .

Why IP Passthrough?

Because the BGW320-500 doesn’t support the superior Bridge mode, we must use IP Passthrough. With Passthrough, we can avoid a situation known as “double-NAT”, which happens when your third-party router is connected behind your AT&T Gateway, slightly increasing latency, and may cause issues with online gaming, port forwarding, etc. Don’t ask me to elaborate… because I don’t know.

Prerequisites

• A third-party router: Something snazzy that’s compatible with your gateway (NETGEAR, TP-Link, ASUS, you get the picture)
• Your router’s Access Code.. You’ll need it later on to bribe– I mean, persuade the Gateway into letting you change the settings
• Ethernet cables: Two, one for your computer to the Gateway, and one for the Gateway to your new router

Note: Before you start, disable Wi-Fi on your AT&T Gateway. Trust me… (Link to router page)

Setting Up

After you have your equipment ready, we can begin.

1. Plug in and turn on your third-party router. As it powers on, connect an Ethernet cable from one of the LAN ports of your AT&T Gateway into the port labelled “WAN” on your third-party router.
   • Note: Connect your computer to the AT&T Gateway via Ethernet too. It’ll make it easier to configure it.
2. Open your AT&T Gateway web portal. It should be http://192.168.1.254 by default.
3. Navigate to the Firewall > IP Passthrough tab (Link). You will need to enter your Access Code to open the IP Passthrough settings.
4. After you enter your Access Code and open the IP Passthrough page, you will be presented with this page:
5. Set the Allocation Mode to Passthrough, and Passthrough Mode to DHCPS-fixed. (If you cannot change the following settings, make sure to press Save after selecting Passthrough)
6. Fill out your third-party router’s MAC address A MAC address (Media Access Control address) is a unique identifier assigned to a network interface controller (NIC) for communication on a network or choose it from the drop-down list. Click Save when you have finished.
7. After you save your changes, continue the process by setting up your third-party router. Given every router out there is different, I can’t provide specific steps for this part.
   • One thing to note, however, is to make sure you set your third-party router’s WAN IP to the public IP assigned by AT&T (whatismyip.com can help you check this). If it’s set to DHCP, you might get the proper IP, or you might get a private IP behind the Gateway’s NAT, which is exactly what causes double-NAT.

Congrats! You have successfully set up a third-party router with Passthrough on your AT&T Gateway. If you have any questions or trouble following the instructions, good luck :D

References

1. AT&T Business ↩