A tunnel that will connect the subnets behind the gateways <b>moon</b>
and <b>sun</b>, respectively, is preconfigured by installing a trap policy
on gateway <b>moon</b> by means of the setting <b>start_action = trap</b> in swanctl.conf.
A subsequent ping issued by client <b>alice</b> behind gateway <b>moon</b> to
<b>bob</b> located behind gateway <b>sun</b> triggers an acquire and
leads to the automatic establishment of the subnet-to-subnet tunnel.
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Upon the successful establishment of the IPsec tunnel, an updown script automatically
inserts iptables-based firewall rules that let pass the traffic tunneled via the
<b>ipsec0</b> tun interface. In order to test both tunnel and firewall, client <b>alice</b>
behind gateway <b>moon</b> pings client <b>bob</b> located behind gateway <b>sun</b>.
