Your question is vague. If I understand. the symptom is that if you are not doing anything, when your allowed machine tries to communicate, it cannot at first but if you ping, it will work after...
If that is the case, then you are observing normal behavior in that the tunnel will go down after a period of time. To bring it back up, you simply have to send it interesting traffic..
The ping works but any traffic destined for that remote side (that's allowed of course) should bring it up.
Chris
