How can I force all internet traffic over a PPTP VPN but still allow local lan access?

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http://serverfault.com – I have a server running Linux Mint 12 that I want to keep connected to a PPTP VPN all the time. The VPN server is pretty reliable, but it drops on occasion so I just want to make it so all internet activity is disabled if the VPN connection is broken. I'd also like to figure out a way to restart it automatically, but that's not as big of an issue since this happens pretty rarely. I also want to always be able to connect to the box from my lan, regardless of whether the VPN is up or not. Here's what my ifconfig looks like with the VPN connected properly: eth0 Link encap:Ethernet HWad (HowTos)