The roadwarriors carol and dave set up a connection to gateway moon. The authentication is based on Pre-Shared Keys (PSK) followed by extended authentication (XAUTH) of carol and dave based on user names and passwords.
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, carol and dave ping the client alice behind the gateway moon.