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503 lines
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<?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-masq</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>masq</refname>
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<refpurpose>Shorewall Masquerade/SNAT definition file</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>/etc/shorewall/masq</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>Use this file to define dynamic NAT (Masquerading) and to define
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Source NAT (SNAT).</para>
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<warning>
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<para>The entries in this file are order-sensitive. The first entry that
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matches a particular connection will be the one that is used.</para>
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</warning>
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<warning>
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<para>If you have more than one ISP, adding entries to this file will
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*not* force connections to go out through a particular ISP. You must use
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PREROUTING entries in <ulink
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url="shorewall-tcrules.html">shorewall-tcrules</ulink>(5) to do
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that.</para>
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</warning>
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<para>The columns in the file are as follows.</para>
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<variablelist>
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<varlistentry>
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<term><emphasis role="bold">INTERFACE</emphasis> - [<emphasis
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role="bold">+</emphasis>]<emphasis>interfacelist</emphasis>[<emphasis
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role="bold">:</emphasis>[<emphasis>digit</emphasis>]][<emphasis
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role="bold">:</emphasis>[<emphasis>address</emphasis>[<emphasis
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role="bold">,</emphasis><emphasis>address</emphasis>]...[<emphasis>exclusion</emphasis>]]</term>
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<listitem>
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<para>Outgoing <emphasis>interfacelist</emphasis>. Prior to
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Shorewall 4.1.4, this must be a single interface name; in 4.1.4 and
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later, this may be a comma-separated list of interface names. This
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is usually your internet interface. If ADD_SNAT_ALIASES=Yes in
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<ulink url="shorewall.conf.html">shorewall.conf</ulink>(5), you may
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add ":" and a <emphasis>digit</emphasis> to indicate that you want
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the alias added with that name (e.g., eth0:0). This will allow the
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alias to be displayed with ifconfig. <emphasis role="bold">That is
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the only use for the alias name; it may not appear in any other
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place in your Shorewall configuratio</emphasis>n.</para>
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<para>Each interface must match an entry in <ulink
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url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5).
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Prior to Shorewall 4.1.4, this must be an exact match.
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Shorewall-perl 4.1.4 and later allow loose matches to wildcard
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entries in <ulink
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url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5). For
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example, <filename class="devicefile">ppp0</filename> in this file
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will match a <ulink
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url="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>The interface may be qualified by adding the character ":"
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followed by a comma-separated list of destination host or subnet
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addresses to indicate that you only want to change the source IP
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address for packets being sent to those particular destinations.
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Exclusion is allowed (see <ulink
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url="shorewall-exclusion.html">shorewall-exclusion</ulink>(5)).</para>
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<para>If you wish to inhibit the action of ADD_SNAT_ALIASES for this
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entry then include the ":" but omit the digit:</para>
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<programlisting> eth0:
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eth2::192.0.2.32/27</programlisting>
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<para>Normally Masq/SNAT rules are evaluated after those for
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one-to-one NAT (defined in <ulink
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url="shorewall-nat.html">shorewall-nat</ulink>(5)). If you want the
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rule to be applied before one-to-one NAT rules, prefix the interface
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name with "+":</para>
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<programlisting> +eth0
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+eth0:192.0.2.32/27
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+eth0:2</programlisting>
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<para>This feature should only be required if you need to insert
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rules in this file that preempt entries in <ulink
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url="shorewall-nat.html">shorewall-nat</ulink>(5).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">SOURCE</emphasis> (Formerly called SUBNET)
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-
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{<emphasis>interface</emphasis>[[:]<emphasis>exclusion</emphasis>]|<emphasis>address</emphasis>[<emphasis
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role="bold">,</emphasis><emphasis>address</emphasis>][<emphasis>exclusion</emphasis>]}</term>
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<listitem>
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<para>Set of hosts that you wish to masquerade. You can specify this
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as an <emphasis>address</emphasis> (net or host) or as an
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<emphasis>interface</emphasis>. If you give the name of an
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interface, the interface must be up before you start the firewall
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(Shorewall will use your main routing table to determine the
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appropriate addresses to masquerade).</para>
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<para>In order to exclude a address of the specified SOURCE, you may
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append an <emphasis>exclusion</emphasis> ("!" and a comma-separated
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list of IP addresses (host or net) that you wish to exclude (see
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<ulink
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url="shorewall-exclusion.html">shorewall-exclusion</ulink>(5))).
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Note that with Shorewall-perl, a colon (":") must appear between an
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<replaceable>interface</replaceable> name and the
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<replaceable>exclusion</replaceable>;</para>
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<para>Example (shorewall-shell):
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eth1!192.168.1.4,192.168.32.0/27</para>
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<para>Example (shorewall-perl):
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eth1:!192.168.1.4,192.168.32.0/27</para>
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<para>In that example traffic from eth1 would be masqueraded unless
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it came from 192.168.1.4 or 196.168.32.0/27</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">ADDRESS</emphasis> (Optional) - [<emphasis
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role="bold">-</emphasis>|<emphasis
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role="bold">NONAT</emphasis>|[<emphasis
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role="bold">SAME:</emphasis>[<emphasis
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role="bold">nodst:</emphasis>]][<emphasis>address-or-address-range</emphasis>[,<emphasis>address-or-address-range</emphasis>]...][:<emphasis>lowport</emphasis><emphasis
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role="bold">-</emphasis><emphasis>highport</emphasis>][<emphasis
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role="bold">:random</emphasis>]|<emphasis
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role="bold">detect</emphasis>|<emphasis
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role="bold">random</emphasis>]</term>
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<listitem>
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<para>If you specify an address here, SNAT will be used and this
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will be the source address. If ADD_SNAT_ALIASES is set to Yes or yes
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in <ulink url="shorewall.conf.html">shorewall.conf</ulink>(5) then
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Shorewall will automatically add this address to the INTERFACE named
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in the first column.</para>
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<para>You may also specify a range of up to 256 IP addresses if you
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want the SNAT address to be assigned from that range in a
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round-robin fashion by connection. The range is specified by
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<emphasis>first.ip.in.range</emphasis>-<emphasis>last.ip.in.range</emphasis>.
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Beginning with Shorewall 4.0.6, you may follow the port range
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with<emphasis role="bold"> :random</emphasis> in which case
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assignment of ports from the list will be random. <emphasis
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role="bold">random</emphasis> may also be specified by itself in
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this column in which case random local port assignments are made for
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the outgoing connections.</para>
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<para>Example: 206.124.146.177-206.124.146.180</para>
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<para>You may also use the special value "detect" which causes
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Shorewall to determine the IP addresses configured on the interface
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named in the INTERFACES column and substitute them in this
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column.</para>
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<para>Finally, you may also specify a comma-separated list of ranges
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and/or addresses in this column.</para>
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<para>This column may not contain DNS Names.</para>
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<para>Normally, Netfilter will attempt to retain the source port
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number. You may cause netfilter to remap the source port by
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following an address or range (if any) by ":" and a port range with
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the format
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<emphasis>lowport</emphasis>-<emphasis>highport</emphasis>. If this
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is done, you must specify "tcp" or "udp" in the PROTO column.</para>
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<para>Examples:</para>
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<programlisting> 192.0.2.4:5000-6000
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:4000-5000</programlisting>
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<para>You can invoke the SAME target rather than the SNAT target by
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prefixing the column contents with <option>SAME:</option>.</para>
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<para>SAME works like SNAT with the exception that the same local IP
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address is assigned to each connection from a local address to a
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given remote address.</para>
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<para>If the <option>nodst:</option> option is included, then the
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same source address is used for a given internal system regardless
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of which remote system is involved.<warning>
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<para>Support for the SAME target is scheduled for removal from
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the Linux kernel in 2008.</para>
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</warning></para>
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<para>If you simply place <emphasis role="bold">NONAT</emphasis> in
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this column, no rewriting of the source IP address or port number
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will be performed. This is useful if you want particular traffic to
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be exempt from the entries that follow in the file.</para>
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<para>If you want to leave this column empty but you need to specify
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the next column then place a hyphen ("-") here.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">PROTO</emphasis> (Optional) - {<emphasis
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role="bold">-</emphasis>|<emphasis>protocol-name</emphasis>|<emphasis>protocol-number</emphasis>}</term>
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<listitem>
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<para>If you wish to restrict this entry to a particular protocol
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then enter the protocol name (from protocols(5)) or number
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here.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">PORT(S)</emphasis> (Optional) -
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[<emphasis>port-name-or-number</emphasis>[,<emphasis>port-name-or-number</emphasis>]...]</term>
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<listitem>
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<para>If the PROTO column specifies TCP (protocol 6) or UDP
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(protocol 17) then you may list one or more port numbers (or names
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from services(5)) separated by commas or you may list a single port
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range
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(<emphasis>lowport</emphasis>:<emphasis>highport</emphasis>).</para>
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<para>Where a comma-separated list is given, your kernel and
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iptables must have multiport match support and a maximum of 15 ports
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may be listed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">IPSEC</emphasis> (Optional) -
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[<emphasis>option</emphasis>[<emphasis
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role="bold">,</emphasis><emphasis>option</emphasis>]...]</term>
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<listitem>
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<para>If you specify a value other than "-" in this column, you must
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be running kernel 2.6 and your kernel and iptables must include
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policy match support.</para>
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<para>Comma-separated list of options from the following. Only
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packets that will be encrypted via an SA that matches these options
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will have their source address changed.</para>
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<variablelist>
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<varlistentry>
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<term><emphasis
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role="bold">reqid=</emphasis><emphasis>number</emphasis></term>
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<listitem>
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<para>where <emphasis>number</emphasis> is specified using
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setkey(8) using the 'unique:<emphasis>number</emphasis> option
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for the SPD level.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">spi=</emphasis><number></term>
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<listitem>
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<para>where <emphasis>number</emphasis> is the SPI of the SA
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used to encrypt/decrypt packets.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">proto=</emphasis><emphasis
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role="bold">ah</emphasis>|<emphasis
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role="bold">esp</emphasis>|<emphasis
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role="bold">ipcomp</emphasis></term>
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<listitem>
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<para>IPSEC Encapsulation Protocol</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis
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role="bold">mss=</emphasis><emphasis>number</emphasis></term>
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<listitem>
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<para>sets the MSS field in TCP packets</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">mode=</emphasis><emphasis
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role="bold">transport</emphasis>|<emphasis
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role="bold">tunnel</emphasis></term>
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<listitem>
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<para>IPSEC mode</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis
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role="bold">tunnel-src=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>
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<listitem>
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<para>only available with mode=tunnel</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis
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role="bold">tunnel-dst=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>
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<listitem>
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<para>only available with mode=tunnel</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">strict</emphasis></term>
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<listitem>
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<para>Means that packets must match all rules.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">next</emphasis></term>
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<listitem>
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<para>Separates rules; can only be used with strict</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">MARK</emphasis> - [<emphasis
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role="bold">!</emphasis>]<emphasis>value</emphasis>[/<emphasis>mask</emphasis>][<emphasis
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role="bold">:C</emphasis>]</term>
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<listitem>
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<para>Defines a test on the existing packet or connection mark. The
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rule will match only if the test returns true.</para>
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<para>If you don't want to define a test but need to specify
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anything in the following columns, place a "-" in this field.</para>
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<variablelist>
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<varlistentry>
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<term>!</term>
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<listitem>
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<para>Inverts the test (not equal)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis>value</emphasis></term>
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<listitem>
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<para>Value of the packet or connection mark.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis>mask</emphasis></term>
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<listitem>
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<para>A mask to be applied to the mark before testing.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><emphasis role="bold">:C</emphasis></term>
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<listitem>
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<para>Designates a connection mark. If omitted, the packet
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mark's value is tested. This option is only supported by
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Shorewall-perl.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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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>Examples</title>
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<variablelist>
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<varlistentry>
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<term>Example 1:</term>
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<listitem>
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<para>You have a simple masquerading setup where eth0 connects to a
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DSL or cable modem and eth1 connects to your local network with
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subnet 192.168.0.0/24.</para>
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<para>Your entry in the file can be either:</para>
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<programlisting> #INTERFACE SOURCE
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eth0 eth1</programlisting>
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<para>or</para>
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<programlisting> #INTERFACE SOURCE
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eth0 192.168.0.0/24</programlisting>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Example 2:</term>
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<listitem>
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<para>You add a router to your local network to connect subnet
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192.168.1.0/24 which you also want to masquerade. You then add a
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second entry for eth0 to this file:</para>
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<programlisting> #INTERFACE SOURCE
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eth0 192.168.1.0/24</programlisting>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Example 3:</term>
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<listitem>
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<para>You have an IPSEC tunnel through ipsec0 and you want to
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masquerade packets coming from 192.168.1.0/24 but only if these
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packets are destined for hosts in 10.1.1.0/24:</para>
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<programlisting> #INTERFACE SOURCE
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ipsec0:10.1.1.0/24 196.168.1.0/24</programlisting>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Example 4:</term>
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<listitem>
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<para>You want all outgoing traffic from 192.168.1.0/24 through eth0
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to use source address 206.124.146.176 which is NOT the primary
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address of eth0. You want 206.124.146.176 to be added to eth0 with
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name eth0:0.</para>
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<programlisting> #INTERFACE SOURCE ADDRESS
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eth0:0 192.168.1.0/24 206.124.146.176</programlisting>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Example 5:</term>
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<listitem>
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<para>You want all outgoing SMTP traffic entering the firewall on
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eth1 to be sent from eth0 with source IP address 206.124.146.177.
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You want all other outgoing traffic from eth1 to be sent from eth0
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with source IP address 206.124.146.176.</para>
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<programlisting> #INTERFACE SOURCE ADDRESS PROTO PORT(S)
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eth0 eth1 206.124.146.177 tcp smtp
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eth0 eth1 206.124.146.176</programlisting>
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<warning>
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<para>The order of the above two rules is significant!</para>
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</warning>
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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>FILES</title>
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|
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<para>/etc/shorewall/masq</para>
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</refsect1>
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<refsect1>
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<title>See ALSO</title>
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<para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
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shorewall-blacklist(5), shorewall-exclusion(5), shorewall-hosts(5),
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shorewall-interfaces(5), shorewall-ipsec(5), shorewall-maclist(5),
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shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
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shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5),
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shorewall-route_rules(5), shorewall-routestopped(5), shorewall-rules(5),
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shorewall.conf(5), shorewall-tcclasses(5), shorewall-tcdevices(5),
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shorewall-tcrules(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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