On the Ppoe configuration screen it says to configure the connection on the net balancer.
Please try this and let me know how it works out:
Goto net balancer and configure your connection and on the fail over monitor make sure the Immediately restart ppoe and 3g is set to yes. Make sure you set at least 1 failover IP so it will have a site to check. I use Google DNS server 184.108.40.206
By using of Google DNS is not a permanent solution could get.Sometime it does not work well..