Seems FON router's PPPoE support is not as good as I thought.
It will keep disconnecting, and even worst, the LAN connection will drop, when there is some large number of traffic, like rsync.
Searched web and find there are 2 things to deal with this problem: 1. hard reset it; 2. change the WAN cable.
I tried hard reset but the problem still here, so I tried to change the WAN cable, seems the connection is more stable now, let me do more test tonight.
