shorewall_code/docs/ipsets.xml

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  <articleinfo>
    <title>Shorewall and Ipsets</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

        <surname>Eastep</surname>
      </author>
    </authorgroup>

    <pubdate>2005-11-20</pubdate>

    <copyright>
      <year>2005</year>

      <holder>Thomas M. Eastep</holder>
    </copyright>

    <legalnotice>
      <para>Permission is granted to copy, distribute and/or modify this
      document under the terms of the GNU Free Documentation License, Version
      1.2 or any later version published by the Free Software Foundation; with
      no Invariant Sections, with no Front-Cover, and with no Back-Cover
      Texts. A copy of the license is included in the section entitled
      <quote><ulink url="GnuCopyright.htm">GNU Free Documentation
      License</ulink></quote>.</para>
    </legalnotice>
  </articleinfo>

  <section>
    <title>What are Ipsets?</title>

    <para>Ipsets are an extention to Netfilter/iptables that are currently
    available in Patch-O-Matic-ng (<ulink
    url="http://www.netfilter.org">http://www.netfilter.org</ulink>). Using
    ipsets requires that you patch your kernel and iptables and that you build
    and install the ipset utility from <ulink
    url="http://ipset.netfilter.org/">http://ipset.netfilter.org/</ulink>.</para>

    <para>Ipset allows you to create one or more named sets of addresses then
    use those sets to define Netfilter/iptables rules. Possible uses of ipsets
    include:</para>

    <orderedlist>
      <listitem>
        <para>Blacklists. Ipsets provide an effecient way to represent large
        sets of addresses and you can maintain the lists without the need to
        restart or even refresh your Shorewall configuration.</para>
      </listitem>

      <listitem>
        <para>Zone definition. Using the /etc/shorewall/hosts file, you can
        define a zone based on the (dynamic) contents of an ipset. Again, you
        can then add or delete addresses to the ipset without restarting
        Shorewall.</para>
      </listitem>
    </orderedlist>

    <para>See the ipsets site (URL above) for additional information about
    ipsets.</para>
  </section>

  <section>
    <title>Shorewall Support for Ipsets</title>

    <para>Support for ipsets was introduced in Shorewall version 2.3.0. In
    most places where a host or network address may be used, you may also use
    the name of an ipset prefaced by "+".</para>

    <para>Example: "+Mirrors"</para>

    <para>The name of the set may optionally followed by:</para>

    <orderedlist numeration="loweralpha">
      <listitem>
        <para>a number from 1 to 6 enclosed in square brackets ([]) -- this
        number indicates the maximum number of ipset binding levels that are
        to be matched. Depending on the context where the ipset name is used,
        either all "src" or all "dst" matches will be used.</para>

        <para>Example: "+Mirrors[4]"</para>
      </listitem>

      <listitem>
        <para>a series of "src" and "dst" options separated by commas and
        inclosed in square brackets ([]). These will be passed directly to
        iptables in the generated --set clause. See the ipset documentation
        for details.</para>

        <para>Example: "+Mirrors[src,dst,src]"</para>

        <para>Note that "+Mirrors[4]" used in the SOURCE column of the rules
        file is equivalent to "+Mirrors[src,src,src,src]".</para>
      </listitem>
    </orderedlist>

    <para>To generate a negative match, prefix the "+" with "!" as in
    "!+Mirrors".</para>

    <para>Example 1: Blacklist all hosts in an ipset named "blacklist"</para>

    <para><filename>/etc/shorewall/blacklist</filename><programlisting>#ADDRESS/SUBNET         PROTOCOL        PORT
+blacklist</programlisting></para>

    <para>Example 2: Allow SSH from all hosts in an ipset named "sshok:</para>

    <para><filename>/etc/shorewall/rules</filename><programlisting>#ACTION      SOURCE      DEST     PROTO    DEST PORT(S)
ACCEPT       +sshok      $FW      tcp      22</programlisting></para>

    <para>Shorewall can automatically manage the contents of your ipsets for
    you. If you specify SAVE_IPSETS=Yes in /etc/shorewall/shorewall.conf then
    "shorewall save" will save the contents of your ipsets. The file where the
    sets are saved is formed by taking the name where the Shorewall
    configuration is stored and appending "-ipsets". So if you enter the
    command "shorewall save standard" then your Shorewall</para>

    <para>Regardless of the setting of SAVE_IPSETS, the <command>shorewall -f
    start</command> and <command>shorewall restore</command> commands will
    restore the ipset contents corresponding to the Shorewall configuration
    restored provided that the saved Shorewall configuration specified
    exists.</para>

    <para>For example, <command>shorewall restore standard</command> would
    restore the ipset contents from
    <filename>/var/lib/shorewall/standard-ipsets</filename> provided that
    <filename>/var/lib/shorewall/standard</filename> exists and is executable
    and that <filename>/var/lib/shorewall/standard-ipsets</filename> exists
    and is executable.</para>

    <para>Also regardless of the setting of SAVE_IPSETS, the
    <command>shorewall forget</command> command will purge the saved ipset
    information (if any) associated with the saved shorewall configuration
    being removed.</para>

    <para>You can also associate ipset contents with Shorewall configuration
    directories using the following command:</para>

    <programlisting><command>ipset -S &gt; &lt;config directory&gt;/ipsets</command></programlisting>

    <para>Example:</para>

    <programlisting><command>ipset -S &gt; /etc/shorewall/ipsets</command></programlisting>

    <para>When you start or restart Shorewall (including using the
    <command>try</command> command) from the configuration directory, your
    ipsets will be configured from the saved ipsets file. Once again, this
    behavior is independent of the setting of SAVE_IPSETS.</para>

    <para>As mentioned above, ipsets are well suited for large blacklists. You
    can maintain your blacklist using the 'ipset' utility without ever having
    to restart or refresh Shorewall. If you use the SAVE_IPSETS=Yes feature
    just be sure to "shorewall save" after altering the blacklist ipset(s).
    Example:</para>

    <para><filename>/etc/shorewall/blacklist</filename>:</para>

    <programlisting>#ADDRESS/SUBNET         PROTOCOL        PORT
+Blacklist[src,dst]
+Blacklistnets[src,dst]</programlisting>

    <para>Create the blacklist ipsets using:</para>

    <programlisting><command>ipset -N Blacklist iphash
ipset -N Blacklistnets nethash</command></programlisting>

    <para>Add entries:</para>

    <programlisting><command>ipset -A Blacklist 206.124.146.177
ipset -A Blacklistnets 206.124.147.0/24</command></programlisting>

    <para>To allow entries for individual ports:</para>

    <programlisting><command>ipset -N SMTP portmap --from 1 --to 31
ipset -A SMTP 25

ipset -A Blacklist 206.124.146.177
ipset -B Blacklist 206.124.146.177 -b SMTP</command></programlisting>

    <para>Now only port 25 will be blocked from 206.124.146.177.</para>
  </section>

  <section>
    <title>Defining Dynamic Zones using Ipsets</title>

    <para>The use of ipsets provides a much better way to define dynamic zones
    than is provided by the native Shorewall implementation. To define a
    dynamic zone of hosts <emphasis role="bold">dyn</emphasis> that interface
    through interface eth3, use:</para>

    <para>/etc/shorewall/zones:</para>

    <programlisting>#ZONE         TYPE         OPTIONS            IN OPTIONS        OUT OPTIONS
dyn           ipv4</programlisting>

    <para>/etc/shorewall/interfaces:</para>

    <programlisting>#ZONE         INTERFACE     OPTIONS
-             eth3          …</programlisting>

    <para>/etc/shorewall/hosts:</para>

    <programlisting>#ZONE         HOSTS         OPTIONS
dyn           eth3:+Dyn</programlisting>

    <para>Now create an ipmap named <emphasis role="bold">Dyn</emphasis> and
    you're all set. You can add and delete addresses from Dyn without having
    to touch Shorewall.</para>
  </section>
</article>