@hda:
Did you see these ?
netwerkje.com/eigen-router
haroldschoemaker.nl/2015/07/eigen-router-achter-een-xs4all-vdsl-aansluiting-3/
https://forum.pfsense.org/index.php?topic=104809.msg584237#msg584237
@David_W:
A switch will do what it is configured to do - tagged operation on a VLAN, untagged operation on a VLAN or no access to the VLAN.
In this case, the VDSL bridge's Ethernet port needs to have access to VLAN 4 and 6, both tagged. pfSense needs interfaces on both those VLANs - the most efficient way is to use a single switch port (or lagg group, if you have such a thing) with access to VLAN 4 and 6, both tagged. The switch must be configured to match what is plugged in to the ports.
For access to the VDSL bridge's management interface, you will probably need access to a third VLAN unless the bridge has a second Ethernet port for management purposes. If the management VLAN must be untagged, you must set the PVID of the switch port to the ID of the VLAN you intend to use for this management interface on your switch as well as configuring the port to have untagged access to the relevant VLAN.
Though I'd get one thing working at once, if you have sufficiently recent firmware on your Vigor 130 and the network interface in your pfSense box supports jumbo frames, I believe you should be able to use RFC 4638 to operate with MTU 1500 over PPPoE on XS4ALL. As of today, this support is built in to pfSense 2.3 builds (which reach beta status today) - all you have to do on 2.3 is set the MTU of your PPPoE interface (likely WAN) to 1500.
I've made an unofficial patch for 2.2.4, 2.2.5 and 2.2.6 - amd64 full installs only. I'd upgrade to 2.2.6 before trying this.
Thank you both for the comments on this. The solution was indeed to tag the vlans on the switches. It all works now. Thanks again!