strange problem with FGT90D and vDSL on Wans

[sw2090]

Hiho,

some tech specs ahead:

Firewall: FGT 90D Firmware v5.4.3

WAN1 connected to a ZyXEL VMG1312-B30A which is in bridge mode with a VDSL Line connected to it

WAN2 dito but with a second VMG1312

Internal14 connected to a CompanConnect (i.e. DSL/Fiber connection with static IP and no dial in)

This all used to work fine until the german Telekom migrated the two VDSL Lines to DeutschlandLan (AllIP) with vectoring.

Since then I cannot bring both lines up any more. 

Credencials are definitely correct and so is the setup of both ZyXELs - figured that out with the fieldservice-technician of Telekom who was at Site. He even upgraded the firmware on the ZyXELs to support vectoring (alas even without vectoring support the lines would work but you won't get the full speed then). The weird thing is that either line will work fine again if you rewire it back to its old place. It seems also to work if you do not use the FGT to do PPOE - the technician tried with his laptop or testing device with success. Also measuring the VDSL Lines did not show anything unusual.

The Logs on the FGT (diag app ppp/pppoe/pppd -1) do not show anything but pppoe starting for the interface and getting the parameters and then terminating after a while.

So I evaluated the capture file of the packet sniffer on the interfaces with Wireshark. This showed me that after PPPOED started on the interface it starts sending PADI Broadcasts but don't get any response for several times and ends up gving in due to timing out finally. Then it all restarts again. It does not get any further on neither interface.

Since even the Telekom Support Staff seems not to be capable of a solution I'd like to ask here if anyone had a similar issue on his/her FGT and can provide me with some tip.

greetings

Sebastian