The roadwarrior carol sets up an IPv6 tunnel connection to gateway moon. The authentication is based on Preshared Keys (PSK) and IPv6 addresses (ID_IPV6_ADDR). firewall=yes automatically inserts ip6tables-based firewall rules that let pass the tunneled traffic. In order to test the tunnel carol sends an IPv6 ICMP request to client alice behind the gateway moon using the ping6 command.