I have a VPN connection between a Cisco 831 and my office's ASA5510 true a DSL modem/router. So the cisco is connected to the Bell modem/router and my pcs are connected on the Cisco
From my office a launch a program that ping the Cisco at each 30 sec. and at each 1 hour i have a dosconnection of the VPN and it goes back on 2 minutes later. If i am connected directly in the modem instead of passing by the router i don't have this trouble. I have the same thing with Videotron connected in a Linksys or Dlink.