The roadwarrior <b>alice</b> sitting behind the NAT router <b>moon</b> sets up a tunnel 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 host <b>alice</b> pings the
client <b>bob</b> behind the gateway <b>sun</b>.