OS X 10.6: Disallow non-VPN connections on wireless?

Question

With the recent rise in awareness of HTTP session hijacking, surfing the internet on a public wireless network has become quite perilous. At my university, the wireless network is totally open --- no encryption at all. Students are encouraged to use VPN, but VPN disconnects when I shut my laptop's lid, and requires a password to reconnect.

Sometimes I don't remember to connect to VPN, and even when I do, I fear that open Facebook/Twitter/other tabs might silently make requests in the background, giving away my sessions before I have a chance to connect.

On Snow Leopard, how can I block any traffic from being transmitted over my wireless card until I am connected to VPN?

My school uses Cisco VPN client, if it matters.

Answer 1

I hacked something together using locationchanger http://tech.inhelsinki.nl/locationchanger/ and ipfw that I am calling OnlyVPN. You would need to fiddle with the firewall rules as I use OpenVPN and not cisco but this might be a good start http://www.gwk.ca/node/65

Answer 2

I found this guy's tutorial the most helpful. He provides a set of rules for adding to Waterroof.

http://aarpol.com/2011/02/block-all-web-traffic-if-vpn-disconnects-or-drops-out-on-osx/