The roadwarriors <b>alice</b> and <b>venus</b> sitting behind the NAT router <b>moon</b> set up
tunnels to gateway <b>sun</b>. UDP encapsulation is used to traverse the NAT router.
<b>leftfirewall=yes</b> automatically inserts iptables-based firewall rules that let pass
the tunneled traffic. In order to test the tunnel, the NAT-ed hosts <b>alice</b> and <b>venus</b>
ping the client <b>bob</b> behind the gateway <b>sun</b>.