The roadwarrior <b>carol</b> sets up a connection to gateway <b>moon</b>.
Using the <b>left|rightprotoport</b> selectors, the IPsec tunnel is
restricted to the ICMP protocol. Upon the successful establishment of the
IPsec tunnel, <b>firewall=yes</b> automatically inserts iptables-based
firewall rules that let pass the tunneled ICMP traffic. In order to test
both tunnel and firewall, <b>carol</b> pings the client <b>alice</b> behind
the gateway <b>moon</b> as well as the inner interface of the gateway.
For the latter ping <b>lefthostaccess=yes</b> is required.
<p>
By default, the native IPsec stack of the Linux 2.6 kernel transmits
protocols and ports not covered by any IPsec SA in the clear. Thus by
selectively opening the firewalls, <b>carol</b> sets up an SSH session to
<b>alice</b> that is not going through the tunnel.
