I'm having persistent problems with Windows PPTP VPN connections. The VPN appears up whilst the tunnel won't transfer traffic (ping to a remote IP within the VPN works for a while, and then fails). The client receives routing information via DHCP. When the connection fails, the routing table is still correct so I don't think it's a routing problem.
My internet connection is via an ADSL2 line.
There's software to deal with PPTP problems, like TunnelRat, but I don't want to install v1.1 of the .NET framework and I'd rather get to the bottom of the problem (I have multiple VPN connections and some are more unreliable than others).
What can I do to get to the bottom of this?
Alternatively, what can I do to keep the connection alive?