@MR.S dear sir, when I connect also my laptop on the LAN I can make the same L2TP connection without a problem. So then the proble, I think isn't at the provider is it? when setting up the L2Tp...

When I am using the ER605 it builds up an L2TP client VPN. Normally I have internet connection on the WAN but now I am at a customer which has not internet. I bought a WIFI dongle which is supported...