VPN (PPTP) connection timeout

["Enrico Corniani" <enrikok gmail com>]

Dear all,
I connect to my adsl modem (speedtouch 546 v6) with a VPN PPTP connection to establish the internet connection.
Evrything works fine, but after a certain time of inactivity the connection doesn't work anymore, well to tell the truth application like torrents or VoIP still works but I can not browse pages (seems like that the dns is not working)
Do you kindly have any idea on how I can solve the problem, I have tried to change the lcp-echo-failure and MTU MRU values but still have the problem.
Thank you very much
Enrico