On Mac I used this resource to block traffic with the exception of UDP and on the ppp0 interface: http://superuser.com/questions/468919/prevent-outgoing-traffic

On Mac I used this resource to block traffic with the exception of UDP and on the ppp0 interface: http://superuser.com/questions/468919/prevent-outgoing-traffic-unless-openvpn-connection-is-active-using-pf-conf-on-ma http://superuser.com/questions/468919/prevent-outgoing-traff...