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Document nat vs. subzone restriction.

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Signed-off-by: Tom Eastep <teastep@shorewall.net>
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Tom Eastep 2014-05-25 10:07:07 -07:00
parent 5a22b14947
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74
Shorewall/manpages/shorewall-nat.xml
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@ -136,6 +136,80 @@
</variablelist>
</refsect1>
<refsect1>
<title>RESTRICTIONS</title>
<para>DNAT rules always preempt one-to-one NAT rules. This has subtile
consequences when there are sub-zones on an
<replaceable>interface</replaceable>. Consider the following:</para>
<para><filename>/etc/shorewall/zones</filename>:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
fw firewall
net ipv4
loc ipv4
smc:net ipv4</programlisting>
<para><filename>/etc/shorewall/interfaces</filename>:</para>
<programlisting>#ZONE INTERFACE OPTIONS
net eth0 dhcp,tcpflags,nosmurfs,routefilter,logmartians,sourceroute=0
loc eth1 tcpflags,nosmurfs,routefilter,logmartians</programlisting>
<para><filename>/etc/shorewall/hosts</filename>:</para>
<programlisting>#ZONE HOST(S) OPTIONS
smc eth0:10.1.10.0/24</programlisting>
<para><filename>/etc/shorewall/nat</filename>:</para>
<programlisting>#EXTERNAL INTERFACE INTERNAL ALL LOCAL
# INTERFACES
10.1.10.100 eth0 172.20.1.100
</programlisting>
<para>Note that the EXTERNAL address is in the <emphasis
role="bold">smc</emphasis> zone.</para>
<para><filename>/etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE USER/ MARK CONNLIMIT TIME HEADERS SWITCH HELPER
# PORT PORT(S) DEST LIMIT GROUP
?SECTION ALL
?SECTION ESTABLISHED
?SECTION RELATED
?SECTION INVALID
?SECTION UNTRACKED
?SECTION NEW
...
DNAT net loc:172.20.1.4 tcp 80</programlisting>
<para>For the one-to-one NAT to work correctly in this configuration, one
of two approaches can be taken:</para>
<orderedlist>
<listitem>
<para>Define a CONTINUE policy with <emphasis
role="bold">smc</emphasis> as the SOURCE zone (preferred):</para>
<programlisting>#SOURCE DEST POLICY LOG LEVEL LIMIT:BURST
<emphasis role="bold">smc $FW CONTINUE</emphasis>
loc net ACCEPT
net all DROP info
# THE FOLLOWING POLICY MUST BE LAST
all all REJECT info
</programlisting>
</listitem>
<listitem>
<para>Set IMPLICIT_CONTINUE=Yes in <ulink
url="manpages/shorewall.conf.html">shorewall.conf(5)</ulink>.</para>
</listitem>
</orderedlist>
</refsect1>
<refsect1>
<title>FILES</title>