The roadwarriors carol and dave set up a connection each
to gateway moon using the MODP Diffie-Hellman Groups 22, 23, and 24
with Prime Order Subgroups.
carol proposes the DH groups MODP_2048_224 and MODP_1024_160 whereas
dave proposes MODP_2048_224 and MODP_2048_256.
Since moon does not support MODP_2048_224 the roadwarriors fall back to
MODP_1024_160 and MODP_2048_256, respectively.
Upon the successful establishment of the IPsec tunnels, leftfirewall=yes
automatically inserts iptables-based firewall rules that let pass the tunneled traffic.
In order to test both tunnel and firewall, both carol and dave ping
the client alice behind the gateway moon.