A connection between the subnets behind the gateways moon and sun is set up. The authentication is based on X.509 certificates. The proprietary IKEv1 fragmentation protocol prevents the IP fragmentation of the IKEv1 messages carrying the large X.509 certificates.
Upon the successful establishment of the IPsec tunnel, leftfirewall=yes automatically inserts iptables-based firewall rules that let pass the tunneled traffic. In order to test both tunnel and firewall, client alice behind gateway moon pings client bob located behind gateway sun.