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Since about two weeks I have a VDSL connection in addition to an ADSL which will be terminated next month. While I do enjoy the bandwidth increase, I quickly discovered that the router which comes with the new subscription does not offer the same functionality as I used to have.
VDSL in Belgium comes by default with a so called B-Box2, a Sagem Webr@cer 3464 rebranded by Belgacom, running a customized Belgacom firmware.
With some hidden command this router offers some basic functionality including dyndns, port-forwarding, but features like VPN are missing.

To overcome these limitations, I decided to start using my AVM Fritzbox 7170 router again, and just use the B-Box2 as a bridge. It proved more challenging than I expected, but I succeeded. Below the step you have to perform to make this to work.

Belgacom B-Box / Sagem 3464 in Bridge mode:

Firstly, start with the basic steps to configure the B-Box2 for operating in bridge mode. Doing more with less is the trick here. Rather than adding special configuration, it turns out the modem is already supporting bridged PPPOE traffic straight out of the box. I just decided to strip some unnecessary configuration to avoid problem;

1. Disable wireless
2. Disable the voip wan interface

Below are some screenshots of the steps to take on a factory default box

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Reconfigure the Fritzbox 7170:

The re-configuration of the Fritzbox is more tricky. To be able to establish a PPPOE connection to your ISP (in my case EDPNET), it is necessary that the router is able to send PPPOE encapsulated packets out of the LAN interface, with a VLAN tag. The VLAN tagging is required for VDSL and is only possible after some configuration tweaks. By default, a fritzbox is able to use the LAN0 interface as pseudo WAN port, however this is normally without VLAN tagging. Your PPPOE requests will time out without response if they are not send with the correct VLAN tagging, in case of EDPNET (and probably Belgacom as well) VLAN ID=10.

I also learned that it is not possible with every firmware version. I was succesful with 29.04.70. Newer firmware versions did cause some problems.

To add VLAN tagging to the IP packets, the following changes need to be made to the ar7.cfg file (in /var/flash). First enable telnet (dial #96*7* from a phone connected to one of the analog or ISDN ports). Telnet into the box, and edit ar7.cfg using the build in nvi editor.

Change / add the following:

Insert the below code, in between the existing piece of code in grey:

       vccs {
                VPI = 1;
                VCI = 32;
                traffic_class = atm_traffic_class_UBR;
                pcr = 0;
                scr = 0;
                priority = 0;
                dsl_encap = dslencap_pppoe;
                vlancfg {
                            vlanencap = vlanencap_class_prio;
                            vlanid = 10;
                            vlanprio = 1;
                           }
               ipbridgeing = no;
               ipbridgeing_igmp = no;
               pppoeforwarding = no;
               connections = "internet", "voip";
        }

Change the following parameters from no to yes:

enabled = yes;
name = "internet";
dsl_encap = dslencap_inherit;
dslinterfacename = "dsl";
no_masquerading = no;
no_firewall = no;
pppoevlanauto = yes;
pppoevlanauto_startwithvlan = yes;
ppptarget = "internet";

and

enabled = yes;
name = "voip";
dsl_encap = dslencap_inherit;
dslinterfacename = "dsl";
no_masquerading = no;
no_firewall = no;
pppoevlanauto = yes;
pppoevlanauto_startwithvlan = yes;
ppptarget = "voip";

The code pppoevlanauto and pppoevlanauto_startwithvlan appears twice in the config.
Lastly, change the default VLAN ID from 7 to 10:

manual_speed = no;
connect_delay_when_synced = 3s;
sync_lost_delay = 0w;
default_tcom_vlan = 10;

After this, it’s just a matter of using the GUI to configure LAN0 as WAN interface, with PPPOE. Screenshots below:

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