AT&T 2wire "router behind router" setup how to

I just switched from Comcast to AT&T U-verse for TV + internet service and was surprised to find out that the AT&T modem has a router built in… ugh…

With Comcast, I had been using my Linksys WRT54GS (with the AMAZING Tomato firmware installed) as my router.  Now, I had to choose between:

  1. Using the AT&T 2Wire router as my only router and put the Linksys box in the closet :(
  2. Figuring out how to setup a “router behind router” configuration so that I could continue to use my Linksys box to manage my LAN.

I chose option 2 :)

I’m no IT guy, so I’m not sure if this is the *best* solution.  However, here’s how I got it working:

  1. Log into your 2wire AT&T router (go to 192.168.1.254 in your browser)
  2. I use the 192.168.1.0 / 255.255.255.0 subnet for my Linksys router which happens to be the same subnet that comes as default on the AT&T 2wire router.  To switch the AT&T 2wire router to a different subnet (172.16.0.0 / 255.255.0.0):
    1. Go to Home Network -> Advanced Settings
    2. If a password prompt appears, enter the password on label attached to the side of the AT&T 2wire router
    3. Check the radio button titled “172.16.0.0 / 255.255.0.0” under Settings -> Private Network
    4. Click “Save”
  3. Attach your router to a free LAN port on the AT&T modem and power it on
  4. On the AT&T modem go to Firewall -> Firewall Settings
  5. Select your router under the “Select a computer”
  6. Check the radio button titled “Allow all applications (DMZplus mode)”
  7. Click “Done”
  8. Reboot everything
  9. Make sure that your personal router is using the AT&T router as the DNS server (in this case, it should be pointing set to 172.20.0.1).  My router had a bunch of static addresses left over, which screwed up the DNS resolution when I first tried this…

What should occur is that your personal router should pick up the SAME IP address as the WAN IP address of AT&T router (yes, you read correctly- the SAME IP address).  The DMZplus will seamlessly forward all ports to your personal router! Everything should work as though the AT&T router is not there. Voilà, it works!

Now, you might be asking yourself- “why would I want to use my own router if AT&T gives me one?”

In my case, it is because of the additional functionality and control I get by using the Tomato firmware.  Tomato has built in dynamic DNS clients, QOS, Static DHCP, and many other great features.  If you think your $49 Linksys router sucks, install Tomato!  It will un-suck it…hehe