Table of Contents

Background

AT&T Uverse service is a triple-play service (internet, phone, and TV) provided by AT&T - depending on what service is available in your area you may be getting FTTH (Fiber to the Home), FTTN (Fiber to the Node), or VDSL (either bonded or unbonded).

FTTN and VDSL both use VDSL2 connectivity from your house to the network. The advantage with FTTN over FTTH is reduced deployment costs for MDUs (Multiple Dwelling Units, such as duplexes or apartment complexes) - AT&T only has to run fiber to a local node that then serves VDSL2 to the customers.

The problem isn't the service, the problem is with the Residential Gateway that AT&T provides. It's a decently powerful unit that allows for triple play services. However, there are a lot of limitations in the RG, namely the limitation of ~8000 NAT sessions, a poor interface with very limited options, and no true passthrough.

But wait! IP Passthrough? Why not just use that? The problem is if you're using IP Passthrough, the RG still tracks all connections going through the RG. Once you hit the connection limit of 8000 connections, which admittedly is more than most people need, the RG will refuse new connections.

I've also had some instances where the RG will spontaneously reboot or crash and hang when under heavy usage. I needed to explore options on how to bypass the RG and use my own (hopefully more sane) DSL modem that doesn't do any connection tracking is just a pure layer 2 bridge between AT&T's VDSL network and my router.

Doing some research, my particular VDSL service is unbonded so it only uses one pair of copper lines. This is important because the only DSL modem that is supported by OpenWRT is the Netgear DM200, which only supports unbonded VDSL.

If you have bonded VDSL service, this will probably not work for you.

Why do we have to use OpenWRT, and not just use the DM200 in bridge mode with the stock firmware? The reason is because AT&T uses EAPOL authentication instead of every other sane DSL provider that uses PPPoE. There are a few benefits to this, namely authentication is provided by certificates and not usernames and passwords, and also there is no need for MTU shifting.

The downside is that in my testing, the DM200 in bridge mode does not forward EAPOL / 802.1x packets to the DSL link. This is by design in bridged interfaces, but there is a workaround for it. However, testing the workaround did not solve the problem.

The solution was to run wpa_supplicant on the DM200 itself so the DM200 can authenticate using EAPOL, then bridge the DSL line to the Ethernet line so raw layer 2 traffic is sent to my router.

In this configuration, the DM200 does not connection tracking and no firewall. The only purpose of the DM200 is to run wpa_supplicant for authentication, and to bridge the DSL and Ethernet links.

Hardware Needed

Software Needed

Setup Netgear DM200 VDSL Modem

The Netgear DM200 VDSL modem needs to be flashed to use OpenWRT, and some prep work needs to be started before we can take down the AT&T UVerse modem. The reason why we have to use OpenWRT for the DM200 modem is because AT&T uses EAPOL for authentication vs every other DSL provider that uses PPPoE. The stock firmware on the Netgear DM200 does have PPPoE support, but no EAPOL. Additionally, I have tried putting the modem into bridge mode and running wpa_supplicant on my router, but no EAP packets are forwarded to AT&T's authenticator through the Netgear DM200 modem's bridge. From my tinkering, the Netgear DM200 uses a standard brctl Linux bridge. However, the standard brctl Linux bridge does not forward EAPOL packets due to it's design. It's possible to force the bridge to forward EAPOL packets but in testing this did not work, either with the stock DM200 firmware or OpenWRT firmware.

In this configuration, we are going to be running wpa_supplicant on the DM200 itself, and bridge the DSL connection to the Ethernet connection. This allows a pure layer 2 bridge between the AT&T DSL network, no MTU shifting, and the DM200 does not use any resources managing or tracking connections besides the layer 2 bridge and running wpa_supplicant.

  1. Head over to https://openwrt.org/toh/netgear/dm200 and flash the OpenWRT firmware to the DM200
  2. After the DM200 comes up, log into the DM200 and reconfigure the eth0 interface to be a DHCP client.
  3. Set the DM200 to apply changes without verification, and then plug the modem into your home network with internet access.
  4. Log into the DM200 again and go into the system settings to synchronize the time to your browser and set your time zone. This is important because the authentication certificates are time dependent.
  5. Change the root password, so the SSH server is activated and you can log into it with SSH
  6. Go to the package manager in the DM200 and install the following packages:
    1. wpa-supplicant
    2. ca-certificates
    3. openssh-sftp-server

Extract Certificates From AT&T UVerse RG

  1. Unzip AT&T RG Uverse firmware package - we're looking for spTurquoise210-700_1.0.29.bin
  2. Disconnect the DSL cable from the UVerse RG.
  3. Log into your UVerse RG and downgrade the firmware with the above firmware file. The process takes several minutes and modem will reboot.
  4. After the modem is running again, go to http://192.168.1.254/cgi-bin/ipalloc.ha and assign yourself a static IP address
  5. Refresh your computer's IP address to make sure you have the private IP address that was assigned.
  6. Log into the UVerse RG again and authenticate
  7. Run the following curl commands to start a telnet server on the UVerse modem. When prompted for the password for the user tech, just hit ENTER. After the last command is executed, the UVerse RG will reboot.
    • curl -k -u tech -H "User-Agent: blah" -H "Connection:Keep-Alive" -d "appid=001&set_data=| echo 28telnet stream tcp nowait root /usr/sbin/telnetd -i -l /bin/nsh > /var/etc/inetd.d/telnet28|" -v --http1.1 https://192.168.1.254:49955/caserver
    • curl -k -u tech -H "User-Agent: blah" -H "Connection:Keep-Alive" -d "appid=001&set_data=| pfs -a /var/etc/inetd.d/telnet28|" -v --http1.1 https://192.168.1.254:49955/caserver
    • curl -k -u tech -H "User-Agent: blah" -H "Connection:Keep-Alive" -d "appid=001&set_data=| pfs -s|" -v --http1.1 https://192.168.1.254:49955/caserver
    • curl -k -u tech -H "User-Agent: blah" -H "Connection:Keep-Alive" -d "appid=001&set_data=| reboot|" -v --http1.1 https://192.168.1.254:49955/caserver
  8. Log into the UVerse RG with PuTTY using the IP address 192.168.1.254 on port 28 using the Telnet selection
  9. Remount root file system as writeable
    • mount -o remount,rw /dev/ubi0 /
  10. Mount the mfg partition which contains the certificates
    • mount mtd:mfg -t jffs2 /mfg
  11. Copy the certificate bundle to the web server directory
    • cp /mfg/mfg.dat /www/att/mfg.dat
  12. Tar and copy the intermediate and root certificates to the web server directory
    • tar -zcvf /www/att/certs.tar.gz /etc/rootcert/
  13. Download the certificate bundle and the intermediate and root certificates:
  14. Throw the UVerse RG into the garbage
    • Don't actually throw it in the garbage, you need to return it when you terminate your service with AT&T otherwise they will bill you a hefty sum.
    • Using the firmware archive that was downloaded earlier, you can step the UVerse back up to the current firmware by flashing 1.0.29, then 1.5.12, then 2.7.1
  15. Extract the mfg_dat_decode utility that was downloaded earlier
  16. Extract the certs.tar.gz archive that was downloaded earlier
  17. Copy the mfg.dat file into the folder with the mfg_dat_decode binary
  18. Copy all of the certificates extracted from certs.tar.gz into the folder with the mfg_dat_decode binary
  19. Run the mfg_dat_decode binary, which will extract and create a tar.gz containing certificates and a wpa_supplicant.conf configuration file.
  20. Extract the tar.gz file - you'll end up with a directory that contains three pem formatted certificates, a sample wpa_supplicant.conf file, and a readme.txt file.

Generate / Uplink wpa_supplicant Files

  1. Create a new text file, and paste the following into it and save it as 99_dsl_eapol.sh - you can also just click on the link below and download it.
    99_dsl_eapol.sh
    #!/bin/sh

logger -t DSL "$DSL_NOTIFICATION_TYPE $DSL_INTERFACE_STATUS"

if [ "$DSL_NOTIFICATION_TYPE" = "DSL_INTERFACE_STATUS" ] && [ "$DSL_INTERFACE_STATUS" = "UP" ]; then
        logger -t DSL "DSL interface UP, starting wpa_supplicant..."
        /usr/sbin/wpa_supplicant -s -B -P /var/run/wpa_supplicant.pid -D wired -i dsl0 -b br-br0 -c /etc/wpa_supplicant/wpa_supplicant.conf
        ip link set eth0 down
        sleep 5
        ip link set eth0 up
fi

if [ "$DSL_NOTIFICATION_TYPE" = "DSL_INTERFACE_STATUS" ] && [ "$DSL_INTERFACE_STATUS" = "DOWN" ]; then
        logger -t DSL "DSL interface DOWN, killing wpa_supplicant..."
        if [ -e /var/run/wpa_supplicant.pid ]; then
                kill $(cat /tmp/run/wpa_supplicant.pid)
        fi
        ip link set eth0 down
fi
  2. Edit the wpa_supplicant.conf file using a text editor.
    • Look for the lines that start with ca_cert, client_cert, and private_key and add /etc/wpa_supplicant/ before the filename. For example: 
      ca_cert="/etc/wpa_supplicant/CA_001E46-27058949910000.pem"
client_cert="/etc/wpa_supplicant/Client_001E46-27058949910000.pem"
eap=TLS
eapol_flags=0
identity="18:9C:27:18:ED:F1" # Internet (ONT) interface MAC address must match this value
key_mgmt=IEEE8021X
phase1="allow_canned_success=1 tls_disable_time_checks=1"
private_key="/etc/wpa_supplicant/PrivateKey_PKCS1_001E46-27058949910000.pem"
  3. Open FileZilla and connect to the DM200 modem using the sftp protocol as the root
  4. Create a new directory /etc/wpa_supplicant
  5. Upload the wpa_supplicant.conf file and the three pem encoded certificates to /etc/wpa_supplicant
  6. Upload the 99_dsl_eapol.sh file to /etc/hotplug.d/dsl and apply 0755 / -rwxr-xr-x permissions
  7. Do not reboot the DM200 from now on, otherwise you will need to factory reset the DM200 and start over
Configure the DM200 And Go Online!
  1. Log into the web interface for the DM200, and delete all of the interfaces. On my default configuration, there was a eth0, dsl0 and dsl0-ipv6 interface.
  2. Create a new eth0 interface and set it to unmanaged
  3. Create a new dsl0 interface and set it to unmanaged
  4. Create a new br0 bridge interface with eth0 and dsl0 as slave interfaces, and set it to unmanaged
  5. Apply changes without verification - at this point the modem will disappear from the network. Wait a few minutes, and then turn it off.
  6. Connect the Ethernet cable to your router and the DSL cable to the phone line.
  7. Set the WAN interface on your router to use vlan 0
  8. Turn on the DM200. After a few minutes it should synchronize and train the DSL line. When training is complete, the DSL light will stop blinking and turn solid green.
  9. A few seconds after the DSL light turns solid green, the Ethernet light should turn off and then back on after 5 seconds.
  10. At this point the DSL modem should have authenticated using EAPOL using wpa_supplicant, and you should be able to get a IP address and access the internet!

Known Problems

Sources and References