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Describe IPSEC via SNAT

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Signed-off-by: Tom Eastep <teastep@shorewall.net>
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Tom Eastep 2018-02-08 14:33:54 -08:00
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docs/IPSEC-2.6.xml
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@ -681,4 +681,65 @@ ipip <emphasis role="bold">vpn</emphasis> 0.0.0.0/0</prog
the INPUT chain.</para>
</important>
</section>
<section>
<title>Using SNAT to Force Traffic over an IPSEC Tunnel</title>
<para>Cases can arise where you need to use an IPSEC tunnel to access a
remote network, but you have no control over the associated security
polices. In such cases, the resulting tunnel is accessible from your
firewall but not from your local networks.</para>
<para>Let's take an example:</para>
<itemizedlist>
<listitem>
<para>Remote gateway 192.0.2.26</para>
</listitem>
<listitem>
<para>Remote subnet 172.22.4.0/24</para>
</listitem>
<listitem>
<para>Your public IP address is 192.0.2.199</para>
</listitem>
<listitem>
<para>Your Internet-facing interface is eth0</para>
</listitem>
<listitem>
<para>Your local network is 192.168.219.0/24</para>
</listitem>
<listitem>
<para>You want to access 172.22.4.0/24 from 192.168.219.0/24</para>
</listitem>
</itemizedlist>
<para>You need to configure as follows.</para>
<para>/etc/shorewall/zones:</para>
<programlisting>#ZONE TYPE OPTIONS
...
vpn ip # Note that the zone <emphasis role="bold">cannot</emphasis> be declared as type ipsec
...</programlisting>
<para>/etc/shorewall/hosts:</para>
<programlisting>#ZONE HOSTS OPTIONS
vpn eth0:172.22.4.0/24 mss=1380,destonly
vpn eth0:0.0.0.0/0 mss=1380,ipsec</programlisting>
<para>/etc/shorewall/snat:</para>
<programlisting>SNAT(192.0.2.199) 192.168.219.0/24 eth0:172.22.4.0/24</programlisting>
<para>/etc/shorewall/tunnels:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY_ZONE
ipsec net 192.0.2.26 vpn</programlisting>
</section>
</article>