I have a VPN setup between a Linksys router and a Netopia router. Netopia provides documentation on how to set this up. It seems fine for the most part, but it seems to drop the connection. The simplest way to explain it is that I can ping a computer on the subnet with success but then I am not able to ping it again. Later on, I can ping it again, but later on, I cannot. How do I troubleshoot this?