I got my D-link DSL 6850U router and connected it to my computer using a wire Ethernet connection.
When i tested the speed using speed net site (speedtest.net) i got disconnected each time i ran a test.
After a call to the ISP (bezeqint) - the techinition told me that it might be a problem between my ethernet card (on board) on my computer and the router or the cable (which was a long one) might be low quality.
The solution was to change the Ethernet adapter settings from "auto-negotiate" to 100 Mbps Half duplex.
(start-> network and sharing center -> change adapter settings -> right click on your ethernet device -> properties -> configure -> advanced tab -> speed & duplex)
some hebrew tags to find this post: בזק מודם ראוטר ניתוקים N600 אינטרנט