shorewall_code/Shorewall/manpages/shorewall-masq.xml

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<refentry>
  <refmeta>
    <refentrytitle>shorewall-masq</refentrytitle>

    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>masq</refname>

    <refpurpose>Shorewall Masquerade/SNAT definition file</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>/etc/shorewall/masq</command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Use this file to define dynamic NAT (Masquerading) and to define
    Source NAT (SNAT).</para>

    <warning>
      <para>The entries in this file are order-sensitive. The first entry that
      matches a particular connection will be the one that is used.</para>
    </warning>

    <warning>
      <para>If you have more than one ISP link, adding entries to this file
      will <emphasis role="bold">not</emphasis> force connections to go out
      through a particular link. You must use entries in <ulink
      url="shorewall-rtrules.html">shorewall-rtrules</ulink>(5) or PREROUTING
      entries in <ulink
      url="shorewall-tcrules.html">shorewall-tcrules</ulink>(5) to do
      that.</para>
    </warning>

    <para>The columns in the file are as follows.</para>

    <variablelist>
      <varlistentry>
        <term><emphasis role="bold">INTERFACE:DEST</emphasis> - {[<emphasis
        role="bold">+</emphasis>]<emphasis>interfacelist</emphasis>[<emphasis
        role="bold">:</emphasis>[<emphasis>digit</emphasis>]][<emphasis
        role="bold">:</emphasis>[<emphasis>dest-address</emphasis>[<emphasis
        role="bold">,</emphasis><emphasis>dest-address</emphasis>]...[<emphasis>exclusion</emphasis>]]|COMMENT}</term>

        <listitem>
          <para>Outgoing <emphasis>interfacelist</emphasis>. This may be a
          comma-separated list of interface names. This is usually your
          internet interface. If ADD_SNAT_ALIASES=Yes in <ulink
          url="shorewall.conf.html">shorewall.conf</ulink>(5), you may add ":"
          and a <emphasis>digit</emphasis> to indicate that you want the alias
          added with that name (e.g., eth0:0). This will allow the alias to be
          displayed with ifconfig. <emphasis role="bold">That is the only use
          for the alias name; it may not appear in any other place in your
          Shorewall configuratio</emphasis>n.</para>

          <para>Each interface must match an entry in <ulink
          url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5).
          Shorewall allows loose matches to wildcard entries in <ulink
          url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5). For
          example, <filename class="devicefile">ppp0</filename> in this file
          will match a <ulink
          url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5)
          entry that defines <filename
          class="devicefile">ppp+</filename>.</para>

          <para>Where <ulink
          url="http://www.shorewall.net/4.4/MultiISP.html#Shared">more that
          one internet provider share a single interface</ulink>, the provider
          is specified by including the provider name or number in
          parentheses:</para>

          <programlisting>        eth0(Avvanta)</programlisting>

          <para>In that case, you will want to specify the interfaces's
          address for that provider in the ADDRESS column.</para>

          <para>The interface may be qualified by adding the character ":"
          followed by a comma-separated list of destination host or subnet
          addresses to indicate that you only want to change the source IP
          address for packets being sent to those particular destinations.
          Exclusion is allowed (see <ulink
          url="shorewall-exclusion.html">shorewall-exclusion</ulink>(5)) as
          are ipset names preceded by a plus sign '+';</para>

          <para>If you wish to inhibit the action of ADD_SNAT_ALIASES for this
          entry then include the ":" but omit the digit:</para>

          <programlisting>        eth0(Avvanta):
        eth2::192.0.2.32/27</programlisting>

          <para>Normally Masq/SNAT rules are evaluated after those for
          one-to-one NAT (defined in <ulink
          url="shorewall-nat.html">shorewall-nat</ulink>(5)). If you want the
          rule to be applied before one-to-one NAT rules, prefix the interface
          name with "+":</para>

          <programlisting>        +eth0
        +eth0:192.0.2.32/27
        +eth0:2</programlisting>

          <para>This feature should only be required if you need to insert
          rules in this file that preempt entries in <ulink
          url="shorewall-nat.html">shorewall-nat</ulink>(5).</para>

          <para>Comments may be attached to Netfilter rules generated from
          entries in this file through the use of COMMENT lines. These lines
          begin with the word COMMENT; the remainder of the line is treated as
          a comment which is attached to subsequent rules until another
          COMMENT line is found or until the end of the file is reached. To
          stop adding comments to rules, use a line with only the word
          COMMENT.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">SOURCE</emphasis> (Formerly called SUBNET)
        -
        {<emphasis>interface</emphasis>|<emphasis>address</emphasis>[<emphasis
        role="bold">,</emphasis><emphasis>address</emphasis>][<emphasis>exclusion</emphasis>]}</term>

        <listitem>
          <para>Set of hosts that you wish to masquerade. You can specify this
          as an <emphasis>address</emphasis> (net or host) or as an
          <emphasis>interface</emphasis> (use of an
          <emphasis>interface</emphasis> is deprecated). If you give the name
          of an interface, the interface must be up before you start the
          firewall and the Shorewall rules compiler will warn you of that
          fact. (Shorewall will use your main routing table to determine the
          appropriate addresses to masquerade).</para>

          <para>The preferred way to specify the SOURCE is to supply one or
          more host or network addresses separated by comma. You may use ipset
          names preceded by a plus sign (+) to specify a set of hosts.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">ADDRESS</emphasis> (Optional) - [<emphasis
        role="bold">-</emphasis>|<emphasis
        role="bold">NONAT</emphasis>|[<emphasis>address-or-address-range</emphasis>[,<emphasis>address-or-address-range</emphasis>]...][:<emphasis>lowport</emphasis><emphasis
        role="bold">-</emphasis><emphasis>highport</emphasis>][<emphasis
        role="bold">:random</emphasis>][:persistent]|<emphasis
        role="bold">detect</emphasis>|<emphasis
        role="bold">random</emphasis>]</term>

        <listitem>
          <para>If you specify an address here, SNAT will be used and this
          will be the source address. If ADD_SNAT_ALIASES is set to Yes or yes
          in <ulink url="shorewall.conf.html">shorewall.conf</ulink>(5) then
          Shorewall will automatically add this address to the INTERFACE named
          in the first column.</para>

          <para>You may also specify a range of up to 256 IP addresses if you
          want the SNAT address to be assigned from that range in a
          round-robin fashion by connection. The range is specified by
          <emphasis>first.ip.in.range</emphasis>-<emphasis>last.ip.in.range</emphasis>.
          You may follow the port range with<emphasis role="bold">
          :random</emphasis> in which case assignment of ports from the list
          will be random. <emphasis role="bold">random</emphasis> may also be
          specified by itself in this column in which case random local port
          assignments are made for the outgoing connections.</para>

          <para>Example: 206.124.146.177-206.124.146.180</para>

          <para>You may follow the port range (or <emphasis
          role="bold">:random</emphasis>) with <emphasis
          role="bold">:persistent</emphasis>. This is only useful when an
          address range is specified and causes a client to be given the same
          source/destination IP pair. This feature replaces the SAME modifier
          which was removed from Shorewall in version 4.4.0. Unlike <emphasis
          role="bold">random</emphasis>, <emphasis
          role="bold">persistent</emphasis> may not be used by itself.</para>

          <para>You may also use the special value "detect" which causes
          Shorewall to determine the IP addresses configured on the interface
          named in the INTERFACES column and substitute them in this
          column.</para>

          <para>Finally, you may also specify a comma-separated list of ranges
          and/or addresses in this column.</para>

          <para>This column may not contain DNS Names.</para>

          <para>Normally, Netfilter will attempt to retain the source port
          number. You may cause netfilter to remap the source port by
          following an address or range (if any) by ":" and a port range with
          the format
          <emphasis>lowport</emphasis>-<emphasis>highport</emphasis>. If this
          is done, you must specify "tcp" or "udp" in the PROTO column.</para>

          <para>Examples:</para>

          <programlisting>        192.0.2.4:5000-6000
        :4000-5000</programlisting>

          <para>If you simply place <emphasis role="bold">NONAT</emphasis> in
          this column, no rewriting of the source IP address or port number
          will be performed. This is useful if you want particular traffic to
          be exempt from the entries that follow in the file.</para>

          <para>If you want to leave this column empty but you need to specify
          the next column then place a hyphen ("-") here.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">PROTO</emphasis> (Optional) - {<emphasis
        role="bold">-</emphasis>|[!]<emphasis>protocol-name</emphasis>|[!]<emphasis>protocol-number</emphasis>}</term>

        <listitem>
          <para>If you wish to restrict this entry to a particular protocol
          then enter the protocol name (from protocols(5)) or number
          here.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">PORT(S)</emphasis> (Optional) -
        [[!]<emphasis>port-name-or-number</emphasis>[,<emphasis>port-name-or-number</emphasis>]...]</term>

        <listitem>
          <para>If the PROTO column specifies TCP (6), UDP (17), DCCP (33),
          SCTP (132) or UDPLITE (136) then you may list one or more port
          numbers (or names from services(5)) or port ranges separated by
          commas.</para>

          <para>Port ranges are of the form
          <emphasis>lowport</emphasis>:<emphasis>highport</emphasis>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">IPSEC</emphasis> (Optional) -
        [<emphasis>option</emphasis>[<emphasis
        role="bold">,</emphasis><emphasis>option</emphasis>]...]</term>

        <listitem>
          <para>If you specify a value other than "-" in this column, you must
          be running kernel 2.6 and your kernel and iptables must include
          policy match support.</para>

          <para>Comma-separated list of options from the following. Only
          packets that will be encrypted via an SA that matches these options
          will have their source address changed.</para>

          <variablelist>
            <varlistentry>
              <term><emphasis
              role="bold">reqid=</emphasis><emphasis>number</emphasis></term>

              <listitem>
                <para>where <emphasis>number</emphasis> is specified using
                setkey(8) using the 'unique:<emphasis>number</emphasis> option
                for the SPD level.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">spi=</emphasis>&lt;number&gt;</term>

              <listitem>
                <para>where <emphasis>number</emphasis> is the SPI of the SA
                used to encrypt/decrypt packets.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">proto=</emphasis><emphasis
              role="bold">ah</emphasis>|<emphasis
              role="bold">esp</emphasis>|<emphasis
              role="bold">ipcomp</emphasis></term>

              <listitem>
                <para>IPSEC Encapsulation Protocol</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">mss=</emphasis><emphasis>number</emphasis></term>

              <listitem>
                <para>sets the MSS field in TCP packets</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">mode=</emphasis><emphasis
              role="bold">transport</emphasis>|<emphasis
              role="bold">tunnel</emphasis></term>

              <listitem>
                <para>IPSEC mode</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">tunnel-src=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>

              <listitem>
                <para>only available with mode=tunnel</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">tunnel-dst=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>

              <listitem>
                <para>only available with mode=tunnel</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">strict</emphasis></term>

              <listitem>
                <para>Means that packets must match all rules.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">next</emphasis></term>

              <listitem>
                <para>Separates rules; can only be used with strict</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">yes</emphasis></term>

              <listitem>
                <para>When used by itself, causes all traffic that will be
                encrypted/encapsulated to match the rule.</para>
              </listitem>
            </varlistentry>
          </variablelist>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">MARK</emphasis> - [<emphasis
        role="bold">!</emphasis>]<emphasis>value</emphasis>[/<emphasis>mask</emphasis>][<emphasis
        role="bold">:C</emphasis>]</term>

        <listitem>
          <para>Defines a test on the existing packet or connection mark. The
          rule will match only if the test returns true.</para>

          <para>If you don't want to define a test but need to specify
          anything in the following columns, place a "-" in this field.</para>

          <variablelist>
            <varlistentry>
              <term>!</term>

              <listitem>
                <para>Inverts the test (not equal)</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis>value</emphasis></term>

              <listitem>
                <para>Value of the packet or connection mark.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis>mask</emphasis></term>

              <listitem>
                <para>A mask to be applied to the mark before testing.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">:C</emphasis></term>

              <listitem>
                <para>Designates a connection mark. If omitted, the packet
                mark's value is tested.</para>
              </listitem>
            </varlistentry>
          </variablelist>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">USER/GROUP</emphasis> (Optional) -
        [<emphasis
        role="bold">!</emphasis>][<emphasis>user-name-or-number</emphasis>][<emphasis
        role="bold">:</emphasis><emphasis>group-name-or-number</emphasis>][<emphasis
        role="bold">+</emphasis><emphasis>program-name</emphasis>]</term>

        <listitem>
          <para>Only locally-generated connections will match if this column
          is non-empty.</para>

          <para>When this column is non-empty, the rule matches only if the
          program generating the output is running under the effective
          <emphasis>user</emphasis> and/or <emphasis>group</emphasis>
          specified (or is NOT running under that id if "!" is given).</para>

          <para>Examples:</para>

          <variablelist>
            <varlistentry>
              <term>joe</term>

              <listitem>
                <para>program must be run by joe</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>:kids</term>

              <listitem>
                <para>program must be run by a member of the 'kids'
                group</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>!:kids</term>

              <listitem>
                <para>program must not be run by a member of the 'kids'
                group</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>+upnpd</term>

              <listitem>
                <para>#program named upnpd</para>

                <important>
                  <para>The ability to specify a program name was removed from
                  Netfilter in kernel version 2.6.14.</para>
                </important>
              </listitem>
            </varlistentry>
          </variablelist>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">SWITCH -
        [!]<replaceable>switch-name</replaceable></emphasis></term>

        <listitem>
          <para>Added in Shorewall 4.5.1 and allows enabling and disabling the
          rule without requiring <command>shorewall restart</command>.</para>

          <para>The rule is enabled if the value stored in
          <filename>/proc/net/nf_condition/<replaceable>switch-name</replaceable></filename>
          is 1. The rule is disabled if that file contains 0 (the default). If
          '!' is supplied, the test is inverted such that the rule is enabled
          if the file contains 0. <replaceable>switch-name</replaceable> must
          begin with a letter and be composed of letters, decimal digits,
          underscores or hyphens. Switch names must be 30 characters or less
          in length.</para>

          <para>Switches are normally <emphasis role="bold">off</emphasis>. To
          turn a switch <emphasis role="bold">on</emphasis>:</para>

          <simplelist>
            <member><command>echo 1 &gt;
            /proc/net/nf_condition/<replaceable>switch-name</replaceable></command></member>
          </simplelist>

          <para>To turn it <emphasis role="bold">off</emphasis> again:</para>

          <simplelist>
            <member><command>echo 0 &gt;
            /proc/net/nf_condition/<replaceable>switch-name</replaceable></command></member>
          </simplelist>

          <para>Switch settings are retained over <command>shorewall
          restart</command>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">ORIGINAL DEST</emphasis> (origdest) -
        [<emphasis
        role="bold">-</emphasis>|<emphasis>address</emphasis>[,<emphasis>address</emphasis>]...[<emphasis>exclusion</emphasis>]|<emphasis>exclusion</emphasis>]</term>

        <listitem>
          <para>(Optional) Added in Shorewall 4.5.6. This column may be
          included and may contain one or more addresses (host or network)
          separated by commas. Address ranges are not allowed. When this
          column is supplied, rules are generated that require that the
          original destination address matches one of the listed addresses. It
          is useful for specifying that SNAT should occur only for connections
          that were acted on by a DNAT when they entered the firewall.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <variablelist>
      <varlistentry>
        <term>Example 1:</term>

        <listitem>
          <para>You have a simple masquerading setup where eth0 connects to a
          DSL or cable modem and eth1 connects to your local network with
          subnet 192.168.0.0/24.</para>

          <para>Your entry in the file will be:</para>

          <programlisting>        #INTERFACE   SOURCE
        eth0    192.168.0.0/24</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 2:</term>

        <listitem>
          <para>You add a router to your local network to connect subnet
          192.168.1.0/24 which you also want to masquerade. You then add a
          second entry for eth0 to this file:</para>

          <programlisting>        #INTERFACE   SOURCE
        eth0         192.168.1.0/24</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 3:</term>

        <listitem>
          <para>You have an IPSEC tunnel through ipsec0 and you want to
          masquerade packets coming from 192.168.1.0/24 but only if these
          packets are destined for hosts in 10.1.1.0/24:</para>

          <programlisting>        #INTERFACE              SOURCE
        ipsec0:10.1.1.0/24      196.168.1.0/24</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 4:</term>

        <listitem>
          <para>You want all outgoing traffic from 192.168.1.0/24 through eth0
          to use source address 206.124.146.176 which is NOT the primary
          address of eth0. You want 206.124.146.176 to be added to eth0 with
          name eth0:0.</para>

          <programlisting>        #INTERFACE              SOURCE          ADDRESS
        eth0:0                  192.168.1.0/24  206.124.146.176</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 5:</term>

        <listitem>
          <para>You want all outgoing SMTP traffic entering the firewall from
          172.20.1.0/29 to be sent from eth0 with source IP address
          206.124.146.177. You want all other outgoing traffic from
          172.20.1.0/29 to be sent from eth0 with source IP address
          206.124.146.176.</para>

          <programlisting>        #INTERFACE   SOURCE           ADDRESS         PROTO   PORT(S)
        eth0         172.20.1.0/29    206.124.146.177 tcp     smtp
        eth0         172.20.1.0/29    206.124.146.176</programlisting>

          <warning>
            <para>The order of the above two rules is significant!</para>
          </warning>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 6:</term>

        <listitem>
          <para>Connections leaving on eth0 and destined to any host defined
          in the ipset <emphasis>myset</emphasis> should have the source IP
          address changed to 206.124.146.177.</para>

          <programlisting>        #INTERFACE              SOURCE          ADDRESS
        eth0:+myset[dst]        -               206.124.146.177</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 7:</term>

        <listitem>
          <para>SNAT outgoing connections on eth0 from 192.168.1.0/24 in
          round-robin fashion between addresses 1.1.1.1, 1.1.1.3, and 1.1.1.9
          (Shorewall 4.5.9 and later).</para>

          <programlisting>/etc/shorewall/tcrules:

       #ACTION   SOURCE         DEST         PROTO   PORT(S)       SOURCE  USER    TEST
       #                                                           PORT(S)
       1-3:CF    192.168.1.0/24 eth0 ; state=NEW

/etc/shorewall/masq:

       #INTERFACE SOURCE         ADDRESS     ...
       eth0       192.168.1.0/24 1.1.1.1 ; mark=1:C
       eth0       192.168.1.0/24 1.1.1.3 ; mark=2:C
       eth0       192.168.1.0/24 1.1.1.4 ; mark=3:C</programlisting>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>FILES</title>

    <para>/etc/shorewall/masq</para>
  </refsect1>

  <refsect1>
    <title>See ALSO</title>

    <para><ulink
    url="http://shorewall.net/configuration_file_basics.htm#Pairs">http://shorewall.net/configuration_file_basics.htm#Pairs</ulink></para>

    <para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
    shorewall-blacklist(5), shorewall-exclusion(5), shorewall-hosts(5),
    shorewall_interfaces(5), shorewall-ipsets(5), shorewall-maclist(5),
    shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
    shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5),
    shorewall-rtrules(5), shorewall-routestopped(5), shorewall-rules(5),
    shorewall.conf(5), shorewall-secmarks(5), shorewall-tcclasses(5),
    shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5),
    shorewall-tunnels(5), shorewall-zones(5)</para>
  </refsect1>
</refentry>