shorewall_code/Shorewall/manpages/shorewall-interfaces.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<refentry>
  <refmeta>
    <refentrytitle>shorewall-interfaces</refentrytitle>

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

  <refnamediv>
    <refname>interfaces</refname>

    <refpurpose>Shorewall interfaces file</refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para>The interfaces file serves to define the firewall's network
    interfaces to Shorewall. The order of entries in this file is not
    significant in determining zone composition.</para>

    <para>Beginning with Shorewall 4.5.3, the interfaces file supports two
    different formats:</para>

    <variablelist>
      <varlistentry>
        <term>FORMAT 1 (default - deprecated)</term>

        <listitem>
          <para>There is a BROADCAST column which can be used to specify the
          broadcast address associated with the interface.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>FORMAT 2</term>

        <listitem>
          <para>The BROADCAST column is omitted.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>The format is specified by a line as follows:</para>

    <blockquote>
      <para><emphasis role="bold">FORMAT {1|2}</emphasis></para>
    </blockquote>

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

    <variablelist>
      <varlistentry>
        <term><emphasis role="bold">ZONE</emphasis> -
        <emphasis>zone-name</emphasis></term>

        <listitem>
          <para>Zone for this interface. Must match the name of a zone
          declared in /etc/shorewall/zones. You may not list the firewall zone
          in this column.</para>

          <para>If the interface serves multiple zones that will be defined in
          the <ulink url="shorewall-hosts.html">shorewall-hosts</ulink>(5)
          file, you should place "-" in this column.</para>

          <para>If there are multiple interfaces to the same zone, you must
          list them in separate entries.</para>

          <para>Example:</para>

          <blockquote>
            <programlisting>#ZONE   INTERFACE       BROADCAST
loc     eth1            -
loc     eth2            -</programlisting>
          </blockquote>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">INTERFACE</emphasis> -
        <emphasis>interface</emphasis><emphasis
        role="bold">[:</emphasis><emphasis>port</emphasis><emphasis
        role="bold">]</emphasis></term>

        <listitem>
          <para>Logical name of interface. Each interface may be listed only
          once in this file. You may NOT specify the name of a "virtual"
          interface (e.g., eth0:0) here; see <ulink
          url="http://www.shorewall.net/FAQ.htm#faq18">http://www.shorewall.net/FAQ.htm#faq18</ulink>.
          If the <option>physical</option> option is not specified, then the
          logical name is also the name of the actual interface.</para>

          <para>You may use wildcards here by specifying a prefix followed by
          the plus sign ("+"). For example, if you want to make an entry that
          applies to all PPP interfaces, use 'ppp+'; that would match ppp0,
          ppp1, ppp2, … Please note that the '+' means '<emphasis
          role="bold">one</emphasis> or more additional characters' so 'ppp'
          does not match 'ppp+'.</para>

          <para>When using Shorewall versions before 4.1.4, care must be
          exercised when using wildcards where there is another zone that uses
          a matching specific interface. See <ulink
          url="shorewall-nesting.html">shorewall-nesting</ulink>(5) for a
          discussion of this problem.</para>

          <para>Shorewall allows '+' as an interface name.</para>

          <para>There is no need to define the loopback interface (lo) in this
          file.</para>

          <para>If a <replaceable>port</replaceable> is given, then the
          <replaceable>interface</replaceable> must have been defined
          previously with the <option>bridge</option> option. The OPTIONS
          column may not contain the following options when a
          <replaceable>port</replaceable> is given.</para>

          <simplelist>
            <member>arp_filter</member>

            <member>arp_ignore</member>

            <member>bridge</member>

            <member>log_martians</member>

            <member>mss</member>

            <member>optional</member>

            <member>proxyarp</member>

            <member>required</member>

            <member>routefilter</member>

            <member>sourceroute</member>

            <member>upnp</member>

            <member>wait</member>
          </simplelist>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><emphasis role="bold">BROADCAST</emphasis> (Optional) -
        {<emphasis role="bold">-</emphasis>|<emphasis
        role="bold">detect</emphasis>|<emphasis>address</emphasis>[,<emphasis>address</emphasis>]...}</term>

        <listitem>
          <para>Only available if FORMAT 1.</para>

          <para>If you use the special value <emphasis
          role="bold">detect</emphasis>, Shorewall will detect the broadcast
          address(es) for you if your iptables and kernel include Address Type
          Match support.</para>

          <para>If your iptables and/or kernel lack Address Type Match support
          then you may list the broadcast address(es) for the network(s) to
          which the interface belongs. For P-T-P interfaces, this column is
          left blank. If the interface has multiple addresses on multiple
          subnets then list the broadcast addresses as a comma-separated
          list.</para>

          <para>If you don't want to give a value for this column but you want
          to enter a value in the OPTIONS column, enter <emphasis
          role="bold">-</emphasis> in this column.</para>
        </listitem>
      </varlistentry>

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

        <listitem>
          <para>A comma-separated list of options from the following list. The
          order in which you list the options is not significant but the list
          should have no embedded white space.</para>

          <variablelist>
            <varlistentry>
              <term><emphasis role="bold">arp_filter[={0|1}]</emphasis></term>

              <listitem>
                <para>If specified, this interface will only respond to ARP
                who-has requests for IP addresses configured on the interface.
                If not specified, the interface can respond to ARP who-has
                requests for IP addresses on any of the firewall's interface.
                The interface must be up when Shorewall is started.</para>

                <para>Only those interfaces with the
                <option>arp_filter</option> option will have their setting
                changed; the value assigned to the setting will be the value
                specified (if any) or 1 if no value is given.</para>

                <para></para>

                <note>
                  <para>This option does not work with a wild-card
                  <replaceable>interface</replaceable> name (e.g., eth0.+) in
                  the INTERFACE column.</para>
                </note>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">arp_ignore</emphasis>[=<emphasis>number</emphasis>]</term>

              <listitem>
                <para>If specified, this interface will respond to arp
                requests based on the value of <emphasis>number</emphasis>
                (defaults to 1).</para>

                <para>1 - reply only if the target IP address is local address
                configured on the incoming interface</para>

                <para>2 - reply only if the target IP address is local address
                configured on the incoming interface and the sender's IP
                address is part from same subnet on this interface's
                address</para>

                <para>3 - do not reply for local addresses configured with
                scope host, only resolutions for global and link</para>

                <para>4-7 - reserved</para>

                <para>8 - do not reply for all local addresses</para>

                <para></para>

                <note>
                  <para>This option does not work with a wild-card
                  <replaceable>interface</replaceable> name (e.g., eth0.+) in
                  the INTERFACE column.</para>
                </note>

                <para></para>

                <warning>
                  <para>Do not specify <emphasis
                  role="bold">arp_ignore</emphasis> for any interface involved
                  in <ulink url="../ProxyARP.htm">Proxy ARP</ulink>.</para>
                </warning>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Checks packets arriving on this interface against the
                <ulink
                url="shorewall-blacklist.html">shorewall-blacklist</ulink>(5)
                file.</para>

                <para>Beginning with Shorewall 4.4.13:</para>

                <itemizedlist>
                  <listitem>
                    <para>If a <replaceable>zone</replaceable> is given in the
                    ZONES column, then the behavior is as if <emphasis
                    role="bold">blacklist</emphasis> had been specified in the
                    IN_OPTIONS column of <ulink
                    url="shorewall-zones.html">shorewall-zones</ulink>(5).</para>
                  </listitem>

                  <listitem>
                    <para>Otherwise, the option is ignored with a
                    warning:</para>

                    <blockquote>
                      <para><emphasis role="bold">WARNING: The 'blacklist'
                      option is ignored on mult-zone
                      interfaces</emphasis></para>
                    </blockquote>
                  </listitem>
                </itemizedlist>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Designates the interface as a bridge. Beginning with
                Shorewall 4.4.7, setting this option also sets
                <option>routeback</option>.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Specify this option when any of the following are
                true:</para>

                <orderedlist spacing="compact">
                  <listitem>
                    <para>the interface gets its IP address via DHCP</para>
                  </listitem>

                  <listitem>
                    <para>the interface is used by a DHCP server running on
                    the firewall</para>
                  </listitem>

                  <listitem>
                    <para>the interface has a static IP but is on a LAN
                    segment with lots of DHCP clients.</para>
                  </listitem>

                  <listitem>
                    <para>the interface is a <ulink
                    url="../SimpleBridge.html">simple bridge</ulink> with a
                    DHCP server on one port and DHCP clients on another
                    port.</para>

                    <note>
                      <para>If you use <ulink
                      url="../bridge-Shorewall-perl.html">Shorewall-perl for
                      firewall/bridging</ulink>, then you need to include
                      DHCP-specific rules in <ulink
                      url="shorewall-rules.html">shorewall-rules</ulink>(8).
                      DHCP uses UDP ports 67 and 68.</para>
                    </note>
                  </listitem>
                </orderedlist>

                <para>This option allows DHCP datagrams to enter and leave the
                interface.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">ignore[=1]</emphasis></term>

              <listitem>
                <para>When specified, causes the generated script to ignore
                up/down events from Shorewall-init for this device.
                Additionally, the option exempts the interface from hairpin
                filtering. When '=1' is omitted, the ZONE column must contain
                '-' and <option>ignore</option> must be the only
                OPTION.</para>

                <para>Beginning with Shorewall 4.5.5, may be specified as
                '<option>ignore=1</option>' which only causes the generated
                script to ignore up/down events from Shorewall-init; hairpin
                filtering is still applied. In this case, the above
                restrictions on the ZONE and OPTIONS columns are
                lifted.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">logmartians[={0|1}]</emphasis></term>

              <listitem>
                <para>Turn on kernel martian logging (logging of packets with
                impossible source addresses. It is strongly suggested that if
                you set <emphasis role="bold">routefilter</emphasis> on an
                interface that you also set <emphasis
                role="bold">logmartians</emphasis>. Even if you do not specify
                the <option>routefilter</option> option, it is a good idea to
                specify <option>logmartians</option> because your distribution
                may have enabled route filtering without you knowing
                it.</para>

                <para>Only those interfaces with the
                <option>logmartians</option> option will have their setting
                changed; the value assigned to the setting will be the value
                specified (if any) or 1 if no value is given.</para>

                <para>To find out if route filtering is set on a given
                <replaceable>interface</replaceable>, check the contents of
                <filename>/proc/sys/net/ipv4/conf/<replaceable>interface</replaceable>/rp_filter</filename>
                - a non-zero value indicates that route filtering is
                enabled.</para>

                <para>Example:</para>

                <programlisting>        teastep@lists:~$ <command>cat /proc/sys/net/ipv4/conf/eth0/rp_filter </command>
        1
        teastep@lists:~$ </programlisting>

                <para></para>

                <note>
                  <para>This option does not work with a wild-card
                  <replaceable>interface</replaceable> name (e.g., eth0.+) in
                  the INTERFACE column.</para>
                </note>

                <blockquote>
                  <para>This option may also be enabled globally in the <ulink
                  url="shorewall.conf.html">shorewall.conf</ulink>(5)
                  file.</para>
                </blockquote>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Connection requests from this interface are compared
                against the contents of <ulink
                url="shorewall-maclist.html">shorewall-maclist</ulink>(5). If
                this option is specified, the interface must be an ethernet
                NIC and must be up before Shorewall is started.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Added in Shorewall 4.0.3. Causes forwarded TCP SYN
                packets entering or leaving on this interface to have their
                MSS field set to the specified
                <replaceable>number</replaceable>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">nets=(<emphasis>net</emphasis>[,...])</emphasis></term>

              <listitem>
                <para>Limit the zone named in the ZONE column to only the
                listed networks. The parentheses may be omitted if only a
                single <replaceable>net</replaceable> is given (e.g.,
                nets=192.168.1.0/24). Limited broadcast to the zone is
                supported. Beginning with Shorewall 4.4.1, multicast traffic
                to the zone is also supported.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">nets=dynamic</emphasis></term>

              <listitem>
                <para>Defines the zone as <firstterm>dynamic</firstterm>.
                Requires ipset match support in your iptables and kernel. See
                <ulink
                url="http://www.shorewall.net/Dynamic.html">http://www.shorewall.net/Dynamic.html</ulink>
                for further information.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>nosmurfs</term>

              <listitem>
                <para>Filter packets for smurfs (packets with a broadcast
                address as the source).</para>

                <para>Smurfs will be optionally logged based on the setting of
                SMURF_LOG_LEVEL in <ulink
                url="shorewall.conf.html">shorewall.conf</ulink>(5). After
                logging, the packets are dropped.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>When <option>optional</option> is specified for an
                interface, Shorewall will be silent when:</para>

                <itemizedlist>
                  <listitem>
                    <para>a <filename
                    class="directory">/proc/sys/net/ipv4/conf/</filename>
                    entry for the interface cannot be modified (including for
                    proxy ARP).</para>
                  </listitem>

                  <listitem>
                    <para>The first address of the interface cannot be
                    obtained.</para>
                  </listitem>
                </itemizedlist>

                <para>May not be specified with <emphasis
                role="bold">required</emphasis>.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">physical</emphasis>=<emphasis
              role="bold"><emphasis>name</emphasis></emphasis></term>

              <listitem>
                <para>Added in Shorewall 4.4.4. When specified, the interface
                or port name in the INTERFACE column is a logical name that
                refers to the name given in this option. It is useful when you
                want to specify the same wildcard port name on two or more
                bridges. See <ulink
                url="http://www.shorewall.net/bridge-Shorewall-perl.html#Multiple">http://www.shorewall.net/bridge-Shorewall-perl.html#Multiple</ulink>.</para>

                <para>If the <emphasis>interface</emphasis> name is a wildcard
                name (ends with '+'), then the physical
                <emphasis>name</emphasis> must also end in '+'.</para>

                <para>If <option>physical</option> is not specified, then it's
                value defaults to the <emphasis>interface</emphasis>
                name.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis role="bold">proxyarp[={0|1}]</emphasis></term>

              <listitem>
                <para>Sets
                /proc/sys/net/ipv4/conf/<emphasis>interface</emphasis>/proxy_arp.
                Do NOT use this option if you are employing Proxy ARP through
                entries in <ulink
                url="shorewall-proxyarp.html">shorewall-proxyarp</ulink>(5).
                This option is intended solely for use with Proxy ARP
                sub-networking as described at: <ulink
                url="http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html">http://tldp.org/HOWTO/Proxy-ARP-Subnet/index.html.
                </ulink></para>

                <para><emphasis role="bold">Note</emphasis>: This option does
                not work with a wild-card <replaceable>interface</replaceable>
                name (e.g., eth0.+) in the INTERFACE column.</para>

                <para>Only those interfaces with the <option>proxyarp</option>
                option will have their setting changed; the value assigned to
                the setting will be the value specified (if any) or 1 if no
                value is given.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Added in Shorewall 4.4.10. If this option is set, the
                firewall will fail to start if the interface is not usable.
                May not be specified together with <emphasis
                role="bold">optional</emphasis>.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>If specified, indicates that Shorewall should include
                rules that allow traffic arriving on this interface to be
                routed back out that same interface. This option is also
                required when you have used a wildcard in the INTERFACE column
                if you want to allow traffic between the interfaces that match
                the wildcard.</para>

                <para>Beginning with Shorewall 4.4.20, if you specify this
                option, then you should also specify either
                <option>sfilter</option> (see below) or
                <option>routefilter</option> on all interfaces (see
                below).</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">routefilter[={0|1|2}]</emphasis></term>

              <listitem>
                <para>Turn on kernel route filtering for this interface
                (anti-spoofing measure).</para>

                <para>Only those interfaces with the
                <option>routefilter</option> option will have their setting
                changes; the value assigned to the setting will be the value
                specified (if any) or 1 if no value is given.</para>

                <para>The value 2 is only available with Shorewall 4.4.5.1 and
                later when the kernel version is 2.6.31 or later. It specifies
                a <firstterm>loose</firstterm> form of reverse path
                filtering.</para>

                <note>
                  <para>This option does not work with a wild-card
                  <replaceable>interface</replaceable> name (e.g., eth0.+) in
                  the INTERFACE column.</para>
                </note>

                <para>This option can also be enabled globally in the <ulink
                url="shorewall.conf.html">shorewall.conf</ulink>(5)
                file.</para>

                <note>
                  <para>There are certain cases where
                  <option>routefilter</option> cannot be used on an
                  interface:</para>

                  <itemizedlist>
                    <listitem>
                      <para>If USE_DEFAULT_RT=Yes in <ulink
                      url="shorewall.conf.html">shorewall.conf</ulink>(5) and
                      the interface is listed in <ulink
                      url="shorewall-providers.html">shorewall-providers</ulink>(5).</para>
                    </listitem>

                    <listitem>
                      <para>If there is an entry for the interface in <ulink
                      url="shorewall-providers.html">shorewall-providers</ulink>(5)
                      that doesn't specify the <option>balance</option>
                      option.</para>
                    </listitem>

                    <listitem>
                      <para>If IPSEC is used to allow a road-warrior to have a
                      local address, then any interface through which the
                      road-warrior might connect cannot specify
                      <option>routefilter</option>.</para>
                    </listitem>
                  </itemizedlist>
                </note>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>rpfilter</term>

              <listitem>
                <para>Added in Shorewall 4.5.7. This is an anti-spoofing
                measure that requires the 'RPFilter Match' capability in your
                iptables and kernel. It provides a more efficient alternative
                to the <option>sfilter</option> option below. It performs a
                function similar to <option>routefilter</option> (see above)
                but works with Multi-ISP configurations that do now use
                balanced routes.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>sfilter=(<emphasis>net</emphasis>[,...])</term>

              <listitem>
                <para>Added in Shorewall 4.4.20. This option provides an
                anti-spoofing alternative to <option>routefilter</option> on
                interfaces where that option cannot be used, but where the
                <option>routeback</option> option is required (on a bridge,
                for example). On these interfaces, <option>sfilter</option>
                should list those local networks that are connected to the
                firewall through other interfaces.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">sourceroute[={0|1}]</emphasis></term>

              <listitem>
                <para>If this option is not specified for an interface, then
                source-routed packets will not be accepted from that interface
                (sets
                /proc/sys/net/ipv4/conf/<emphasis>interface</emphasis>/accept_source_route
                to 1). Only set this option if you know what you are doing.
                This might represent a security risk and is usually
                unneeded.</para>

                <para>Only those interfaces with the
                <option>sourceroute</option> option will have their setting
                changed; the value assigned to the setting will be the value
                specified (if any) or 1 if no value is given.</para>

                <para></para>

                <note>
                  <para>This option does not work with a wild-card
                  <replaceable>interface</replaceable> name (e.g., eth0.+) in
                  the INTERFACE column.</para>
                </note>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Packets arriving on this interface are checked for
                certain illegal combinations of TCP flags. Packets found to
                have such a combination of flags are handled according to the
                setting of TCP_FLAGS_DISPOSITION after having been logged
                according to the setting of TCP_FLAGS_LOG_LEVEL.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>Incoming requests from this interface may be remapped
                via UPNP (upnpd). See <ulink
                url="../UPnP.html">http://www.shorewall.net/UPnP.html</ulink>.</para>
              </listitem>
            </varlistentry>

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

              <listitem>
                <para>This option is intended for laptop users who always run
                Shorewall on their system yet need to run UPnP-enabled client
                apps such as Transmission (BitTorrent client). The option
                causes Shorewall to detect the default gateway through the
                interface and to accept UDP packets from that gateway. Note
                that, like all aspects of UPnP, this is a security hole so use
                this option at your own risk.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><emphasis
              role="bold">wait</emphasis>=<emphasis>seconds</emphasis></term>

              <listitem>
                <para>Added in Shorewall 4.4.10. Causes the generated script
                to wait up to <emphasis>seconds</emphasis> seconds for the
                interface to become usable before applying the <emphasis
                role="bold">required</emphasis> or <emphasis
                role="bold">optional</emphasis> options.</para>
              </listitem>
            </varlistentry>
          </variablelist>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>

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

        <listitem>
          <para>Suppose you have eth0 connected to a DSL modem and eth1
          connected to your local network and that your local subnet is
          192.168.1.0/24. The interface gets its IP address via DHCP from
          subnet 206.191.149.192/27. You have a DMZ with subnet 192.168.2.0/24
          using eth2. Your iptables and/or kernel do not support "Address Type
          Match" and you prefer to specify broadcast addresses explicitly
          rather than having Shorewall detect them.</para>

          <para>Your entries for this setup would look like:</para>

          <programlisting>FORMAT 1
#ZONE   INTERFACE BROADCAST        OPTIONS
net     eth0      206.191.149.223  dhcp
loc     eth1      192.168.1.255
dmz     eth2      192.168.2.255</programlisting>
        </listitem>
      </varlistentry>

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

        <listitem>
          <para>The same configuration without specifying broadcast addresses
          is:</para>

          <programlisting>FORMAT 2
#ZONE   INTERFACE OPTIONS
net     eth0      dhcp
loc     eth1      
dmz     eth2</programlisting>
        </listitem>
      </varlistentry>

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

        <listitem>
          <para>You have a simple dial-in system with no ethernet
          connections.</para>

          <programlisting>FORMAT 2
#ZONE   INTERFACE OPTIONS
net     ppp0      -</programlisting>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Example 4 (Shorewall 4.4.9 and later):</term>

        <listitem>
          <para>You have a bridge with no IP address and you want to allow
          traffic through the bridge.</para>

          <programlisting>FORMAT 2
#ZONE   INTERFACE OPTIONS
-       br0       routeback</programlisting>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>FILES</title>

    <para>/etc/shorewall/interfaces</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-hosts(5), shorewall-maclist(5),
    shorewall-masq(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>