MacOS: How to block traffic until a VPN connection is established?

Question

VPN

I work on the network exclusively through VPN connections. I'm using OSX 10.9.2, TunnelBrick and the OpenVPN protocol.
After a Wi-Fi connection, it takes a few seconds before the VPN connection is established.
During these few seconds, various applications have time to send their traffic.
How can I block all traffic on "clear" Wi-Fi until a VPN connection is established?
Thank you.
UPD1: Found a solution: Little Snitch allows you to set up profiles and automatically activate them when using different networks.
I'll leave this question here, maybe it will be useful to someone.

Answer 1

ipfw to help you
Examples
hints.macworld.com/comment.php?mode=view&cid=54629
blog.scottlowe.org/2012/04/05/setting-up-ipfw-on-m...
PS. ipfw is already deprecated - asking to use pfctl
Example - blog.scottlowe.org/2013/05/15/using-pf-on-os-x-mou...