A connection between the subnets behind the gateways <b>moon</b> and <b>sun</b> is set up.
The authentication is based on <b>X.509 certificates</b> containing <b>RFC 3779 IP address
block constraints</b>. Both <b>moon</b> and <b>sun</b> set <b>remote_ts = 0.0.0.0/0</b> thus
allowing the peers to narrow down the address range to their actual subnets <b>10.1.0.0/16</b>
and <b>10.2.0.0/16</b>, respectively. These unilaterally proposed traffic selectors must be
validated by corresponding IP address block constraints.
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In addition to that <b>moon</b> sets its local subnet to <b>10.0.0.0/14</b> but
which is automatically narrowed down to <b>10.1.0.0/16</b> by <b>sun</b>
matching it to the IP address constraint in <b>moon</b>'s certificate.
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Upon the successful establishment of the IPsec tunnel, the updown script automatically
inserts iptables-based firewall rules that let pass the tunneled traffic.
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>.
