I am running a Linux based PPTP server behind the RVS4000 (18.104.22.168) and I have issues with keeping the tunnel active (though it states connected).
This is difficult to describe, so here are the symptoms.
I can establish a VPN connection without problem and if I quickly open a terminal and begin to ping something on the LAN, I have no issues with the VPN tunnel in terms of availability and responsiveness.
If I stop pinging and just try to access services as usual that are available on the LAN, the responsiveness is random at best.
The amount of time between the ping stop and the start of this odd behavior is 10 seconds or less. Once the odd behavior starts I can once again try and ping something on the LAN watching the pings fail a dozen times and then all of a sudden they pickup again and continue to ACK as long as I ping.
This seems like some kind of connection timeout or possibly a GRE issue, but the IP Conntrack windows suggests that there connection is still established.
Steps to repeat.
1. Establish a PPTP based VPN connection (client doesn't seem to matter)
2. Observer that one can readily ping a LAN IP within the VPN, then stop pinging
3. Wait 10 or more seconds
4. Start pinging again and observe that the tunnel appears to be stale for a dozen pings or so...
Shane M. Walton