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233 lines
8.5 KiB
XML
233 lines
8.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<refentry>
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<refmeta>
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<refentrytitle>shorewall-nat</refentrytitle>
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<manvolnum>5</manvolnum>
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<refmiscinfo>Configuration Files</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>nat</refname>
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<refpurpose>Shorewall one-to-one NAT file</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>/etc/shorewall/nat</command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>This file is used to define one-to-one Network Address Translation
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(NAT).</para>
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<warning>
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<para>If all you want to do is simple port forwarding, do NOT use this
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file. See <ulink
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url="/FAQ.htm#faq1">http://www.shorewall.net/FAQ.htm#faq1</ulink>. Also,
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in many cases, Proxy ARP (<ulink
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url="/manpages/shorewall-proxyarp.html">shorewall-proxyarp</ulink>(5))
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is a better solution that one-to-one NAT.</para>
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</warning>
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<para>The columns in the file are as follows (where the column name is
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followed by a different name in parentheses, the different name is used in
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the alternate specification syntax).</para>
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<variablelist>
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<varlistentry>
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<term><emphasis role="bold">EXTERNAL</emphasis> -
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{<emphasis>address</emphasis>|?COMMENT}</term>
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<listitem>
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<para>External IP Address - this should NOT be the primary IP
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address of the interface named in the next column and must not be a
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DNS Name.</para>
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<para>If you put ?COMMENT in this column, the rest of the line will
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be attached as a comment to the Netfilter rule(s) generated by the
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following entries in the file. The comment will appear delimited by
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"/* ... */" in the output of "shorewall show nat"</para>
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<para>To stop the comment from being attached to further rules,
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simply include ?COMMENT on a line by itself.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">INTERFACE</emphasis> -
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<emphasis>interfacelist</emphasis>[<emphasis
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role="bold">:</emphasis>[<emphasis>digit</emphasis>]]</term>
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<listitem>
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<para>Interfaces that have the <emphasis
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role="bold">EXTERNAL</emphasis> address. If ADD_IP_ALIASES=Yes in
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<ulink
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url="/manpages/shorewall.conf.html">shorewall.conf</ulink>(5),
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Shorewall will automatically add the EXTERNAL address to this
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interface. Also if ADD_IP_ALIASES=Yes, you may follow the interface
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name with ":" and a <emphasis>digit</emphasis> to indicate that you
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want Shorewall to add the alias with this name (e.g., "eth0:0").
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That allows you to see the alias with ifconfig. <emphasis
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role="bold">That is the only thing that this name is good for -- you
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cannot use it anywhere else in your Shorewall configuration.
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</emphasis></para>
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<para>Each interface must match an entry in <ulink
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url="/manpages/shorewall-interfaces.html">shorewall-interfaces</ulink>(5).
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Shorewall allows loose matches to wildcard entries in <ulink
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url="/manpages/shorewall-interfaces.html">shorewall-interfaces</ulink>(5).
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For example, <filename class="devicefile">ppp0</filename> in this
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file will match a <ulink
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url="/manpages/shorewall-interfaces.html">shorewall-interfaces</ulink>(5)
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entry that defines <filename
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class="devicefile">ppp+</filename>.</para>
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<para>If you want to override ADD_IP_ALIASES=Yes for a particular
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entry, follow the interface name with ":" and no digit (e.g.,
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"eth0:").</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">INTERNAL</emphasis> -
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<emphasis>address</emphasis></term>
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<listitem>
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<para>Internal Address (must not be a DNS Name).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">ALLINTS</emphasis> - [<emphasis
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role="bold">Yes</emphasis>|<emphasis role="bold">No</emphasis>]</term>
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<listitem>
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<para>If Yes or yes, NAT will be effective from all hosts. If No or
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no (or left empty) then NAT will be effective only through the
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interface named in the <emphasis role="bold">INTERFACE</emphasis>
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column.</para>
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<para>This column was formerly labelled ALL INTERFACES.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">LOCAL</emphasis> - [<emphasis
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role="bold">Yes</emphasis>|<emphasis role="bold">No</emphasis>]</term>
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<listitem>
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<para>If <emphasis role="bold">Yes</emphasis> or <emphasis
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role="bold">yes</emphasis>, NAT will be effective from the firewall
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system</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>RESTRICTIONS</title>
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<para>DNAT rules always preempt one-to-one NAT rules. This has subtile
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consequences when there are sub-zones on an
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<replaceable>interface</replaceable>. Consider the following:</para>
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<para><filename>/etc/shorewall/zones</filename>:</para>
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<programlisting>#ZONE TYPE OPTIONS IN OUT
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# OPTIONS OPTIONS
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fw firewall
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net ipv4
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loc ipv4
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smc:net ipv4</programlisting>
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<para><filename>/etc/shorewall/interfaces</filename>:</para>
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<programlisting>#ZONE INTERFACE OPTIONS
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net eth0 dhcp,tcpflags,nosmurfs,routefilter,logmartians,sourceroute=0
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loc eth1 tcpflags,nosmurfs,routefilter,logmartians</programlisting>
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<para><filename>/etc/shorewall/hosts</filename>:</para>
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<programlisting>#ZONE HOST(S) OPTIONS
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smc eth0:10.1.10.0/24</programlisting>
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<para><filename>/etc/shorewall/nat</filename>:</para>
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<programlisting>#EXTERNAL INTERFACE INTERNAL ALLINTS LOCAL
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10.1.10.100 eth0 172.20.1.100
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</programlisting>
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<para>Note that the EXTERNAL address is in the <emphasis
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role="bold">smc</emphasis> zone.</para>
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<para><filename>/etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT ORIGDEST RATE USER MARK CONNLIMIT TIME HEADERS SWITCH HELPER
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?SECTION ALL
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?SECTION ESTABLISHED
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?SECTION RELATED
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?SECTION INVALID
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?SECTION UNTRACKED
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?SECTION NEW
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...
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DNAT net loc:172.20.1.4 tcp 80</programlisting>
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<para>For the one-to-one NAT to work correctly in this configuration, one
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of two approaches can be taken:</para>
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<orderedlist>
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<listitem>
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<para>Define a CONTINUE policy with <emphasis
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role="bold">smc</emphasis> as the SOURCE zone (preferred):</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL LIMIT:BURST
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<emphasis role="bold">smc $FW CONTINUE</emphasis>
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loc net ACCEPT
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net all DROP info
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# THE FOLLOWING POLICY MUST BE LAST
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all all REJECT info
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</programlisting>
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</listitem>
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<listitem>
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<para>Set IMPLICIT_CONTINUE=Yes in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf(5)</ulink>.</para>
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</listitem>
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</orderedlist>
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</refsect1>
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<refsect1>
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<title>FILES</title>
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<para>/etc/shorewall/nat</para>
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</refsect1>
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<refsect1>
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<title>See ALSO</title>
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<para><ulink
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url="/NAT.htm">http://www.shorewall.net/NAT.htm</ulink></para>
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<para><ulink
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url="/configuration_file_basics.htm#Pairs">http://www.shorewall.net/configuration_file_basics.htm#Pairs</ulink></para>
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<para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
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shorewall-blacklist(5), shorewall-hosts(5), shorewall_interfaces(5),
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shorewall-ipsets(5), shorewall-maclist(5), shorewall-masq(5),
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shorewall-netmap(5), shorewall-params(5), shorewall-policy(5),
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shorewall-providers(5), shorewall-proxyarp(5), shorewall-rtrules(5),
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shorewall-routestopped(5), shorewall-rules(5), shorewall.conf(5),
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shorewall-secmarks(5), shorewall-tcclasses(5), shorewall-tcdevices(5),
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shorewall-mangle(5), shorewall-tos(5), shorewall-tunnels(5),
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shorewall-zones(5)</para>
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</refsect1>
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</refentry>
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