shorewall_code/docs/blacklisting_support.xml

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  <articleinfo>
    <title>Shorewall Blacklisting/Whitelisting Support</title>

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

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

    <pubdate><?dbtimestamp format="Y/m/d"?></pubdate>

    <copyright>
      <year>2002-2006</year>

      <year>2010</year>

      <year>2011</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>

  <caution>
    <para><emphasis role="bold">This article applies to Shorewall 4.4 and
    later. If you are running a version of Shorewall earlier than Shorewall
    4.3.5 then please see the documentation for that
    release.</emphasis></para>
  </caution>

  <section id="Intro">
    <title>Introduction</title>

    <para>Shorewall supports two different types of blackliisting; rule-based,
    static and dynamic. The BLACKLISTNEWONLY option in
    /etc/shorewall/shorewall.conf controls the degree of blacklist
    filtering:</para>

    <orderedlist>
      <listitem>
        <para>BLACKLISTNEWONLY=No -- All incoming packets are checked against
        the blacklist. New blacklist entries can be used to terminate existing
        connections.</para>
      </listitem>

      <listitem>
        <para>BLACKLISTNEWONLY=Yes -- The blacklists are only consulted for
        new connection requests. Blacklists may not be used to terminate
        existing connections.</para>
      </listitem>
    </orderedlist>
  </section>

  <section>
    <title>Rule-based Blacklisting</title>

    <para>Beginning with Shorewall 4.4.25, the preferred method of
    blacklisting and whitelisting is to use the blrules file (<ulink
    url="manpages/shorewall-blrules.html">shorewall-blrules</ulink> (5)).
    There you have access to the DROP, ACCEPT, REJECT and WHITELIST actions,
    standard and custom macros as well as standard and custom actions. See
    <ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5) for
    details.</para>

    <para>Example:</para>

    <programlisting>#ACTION         SOURCE                  DEST                    PROTO   DEST
#                                                                       PORTS(S)
SECTION BLACKLIST
WHITELIST       net:70.90.191.126       all
DROP            net                     all                     udp     1023:1033,1434,5948,23773
DROP            all                     net                     udp     1023:1033
DROP            net                     all                     tcp     57,1433,1434,2401,2745,3127,3306,3410,4899,5554,5948,6101,8081,9898,23773
DROP            net:221.192.199.48      all
DROP            net:61.158.162.9        all
DROP            net:81.21.54.100        all                     tcp     25
DROP            net:84.108.168.139      all                             
DROP            net:200.55.14.18        all
</programlisting>

    <para>Beginning with Shorewall 4.4.26, the <command>update</command>
    command supports a <option>-b</option> option that causes your legacy
    blacklisting configuration to use the blrules file.</para>

    <note>
      <para>If you prefer to keep your blacklisting rules in your rules file
      (<ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink>
      (5)), you can place them in the BLACKLIST section of that file rather
      than in blrules.</para>
    </note>
  </section>

  <section>
    <title>Legacy Blacklisting</title>

    <para>Prior to 4.4.25, two forms of blacklisting were supported; static
    and dynamic. The dynamic variety is still appropriate for
    <firstterm>on-the-fly</firstterm> blacklisting; the static form is
    deprecated.</para>

    <important>
      <para><emphasis role="bold">By default, only the source address is
      checked against the blacklists</emphasis>. Blacklists only stop
      blacklisted hosts from connecting to you — they do not stop you or your
      users from connecting to blacklisted hosts .</para>

      <variablelist>
        <varlistentry>
          <term>UPDATE</term>

          <listitem>
            <para>Beginning with Shorewall 4.4.12, you can also blacklist by
            destination address. See <ulink
            url="manpages/shorewall-blacklist.html">shorewall-blacklist</ulink>
            (5) and <ulink url="manpages/shorewall.html">shorewall</ulink> (8)
            for details.</para>
          </listitem>
        </varlistentry>
      </variablelist>
    </important>

    <important>
      <para><emphasis role="bold">Dynamic Shorewall blacklisting is not
      appropriate for blacklisting 1,000s of different addresses. Static
      Blacklisting can handle large blacklists but only if you use
      ipsets</emphasis>. Without ipsets, the blacklists will take forever to
      load, and will have a very negative effect on firewall
      performance.</para>
    </important>

    <section id="Static">
      <title>Static Blacklisting</title>

      <para>Shorewall static blacklisting support has the following
      configuration parameters:</para>

      <itemizedlist>
        <listitem>
          <para>You specify whether you want packets from blacklisted hosts
          dropped or rejected using the BLACKLIST_DISPOSITION setting in
          <ulink
          url="manpages/shorewall.conf.html"><filename>shorewall.conf</filename>(5).</ulink></para>
        </listitem>

        <listitem>
          <para>You specify whether you want packets from blacklisted hosts
          logged and at what syslog level using the BLACKLIST_LOGLEVEL setting
          in <ulink
          url="manpages/shorewall.conf.html"><filename>shorewall.conf</filename></ulink>(5).</para>
        </listitem>

        <listitem>
          <para>You list the IP addresses/subnets that you wish to blacklist
          in <ulink
          url="manpages/shorewall-blacklist.html"><filename>shorewall-blacklist</filename></ulink>
          (5). You may also specify PROTOCOL and Port numbers/Service names in
          the blacklist file.</para>
        </listitem>

        <listitem>
          <para>You specify the interfaces whose incoming packets you want
          checked against the blacklist using the <quote>blacklist</quote>
          option in <ulink
          url="manpages/shorewall-interfaces.html"><filename>shorewall-interfaces</filename></ulink>(5)
          (<ulink
          url="manpages/shorewall-zones.html">shorewall-zones</ulink>(5) in
          Shorewall 4.4.12 and later).</para>
        </listitem>
      </itemizedlist>

      <para>Prior to Shorewall 4.4.20, only source-address static blacklisting
      was supported.</para>

      <para>Users with a large static black list may want to set the
      DELAYBLACKLISTLOAD option in shorewall.conf (added in Shorewall version
      2.2.0). When DELAYBLACKLISTLOAD=Yes, Shorewall will enable new
      connections before loading the blacklist rules. While this may allow
      connections from blacklisted hosts to slip by during construction of the
      blacklist, it can substantially reduce the time that all new connections
      are disabled during "shorewall [re]start".</para>

      <para>Beginning with Shorewall 2.4.0, you can use <ulink
      url="ipsets.html">ipsets</ulink> to define your static blacklist. Here's
      an example:</para>

      <programlisting>#ADDRESS/SUBNET         PROTOCOL        PORT
+Blacklistports[dst]
+Blacklistnets[src,dst]
+Blacklist[src,dst]
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>

      <para>In this example, there is a portmap ipset
      <emphasis>Blacklistports</emphasis> that blacklists all traffic with
      destination ports included in the ipset. There are also
      <emphasis>Blacklistnets</emphasis> (type <emphasis>nethash</emphasis>)
      and <emphasis>Blacklist</emphasis> (type <emphasis>iphash</emphasis>)
      ipsets that allow blacklisting networks and individual IP addresses.
      Note that [src,dst] is specified so that individual entries in the sets
      can be bound to other portmap ipsets to allow blacklisting
      (<emphasis>source address</emphasis>, <emphasis>destination
      port</emphasis>) combinations. For example:</para>

      <programlisting>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</programlisting>

      <para>This will blacklist SMTP traffic from host 206.124.146.177.</para>
    </section>

    <section id="whitelisting">
      <title>Static Whitelisting</title>

      <para>Beginning with Shorewall 4.4.20, you can create
      <firstterm>whitelist</firstterm> entries in the blacklist file.
      Connections/packets matching a whitelist entry are not matched against
      the entries in the blacklist file that follow. Whitelist entries are
      created using the <emphasis role="bold">whitelist</emphasis> option
      (OPTIONS column). See <ulink
      url="manpages/shorewall-blacklist.html"><filename>shorewall-blacklist</filename></ulink>
      (5).</para>
    </section>

    <section id="Dynamic">
      <title>Dynamic Blacklisting</title>

      <para>Beginning with Shorewall 4.4.7, dynamic blacklisting is enabled by
      setting DYNAMIC_BLACKLIST=Yes in <filename>shorewall.conf</filename>.
      Prior to that release, the feature is always enabled.</para>

      <para>Once enabled, dynamic blacklisting doesn't use any configuration
      parameters but is rather controlled using /sbin/shorewall[-lite]
      commands. <emphasis role="bold">Note</emphasis> that <emphasis
      role="bold">to</emphasis> and <emphasis role="bold">from</emphasis> may
      only be specified when running <emphasis role="bold">Shorewall 4.4.12 or
      later</emphasis>.</para>

      <itemizedlist>
        <listitem>
          <para>drop [to|from] <emphasis>&lt;ip address list&gt;</emphasis> -
          causes packets from the listed IP addresses to be silently dropped
          by the firewall.</para>
        </listitem>

        <listitem>
          <para>reject [to|from]<emphasis>&lt;ip address list&gt;</emphasis> -
          causes packets from the listed IP addresses to be rejected by the
          firewall.</para>
        </listitem>

        <listitem>
          <para>allow [to|from] <emphasis>&lt;ip address list&gt;</emphasis> -
          re-enables receipt of packets from hosts previously blacklisted by a
          <emphasis>drop</emphasis> or <emphasis>reject</emphasis>
          command.</para>
        </listitem>

        <listitem>
          <para>save - save the dynamic blacklisting configuration so that it
          will be automatically restored the next time that the firewall is
          restarted.</para>

          <para><emphasis role="bold">Update:</emphasis> Beginning with
          Shorewall 4.4.10, the dynamic blacklist is automatically retained
          over <command>stop/start</command> sequences and over
          <command>restart</command>.</para>
        </listitem>

        <listitem>
          <para>show dynamic - displays the dynamic blacklisting
          configuration.</para>
        </listitem>

        <listitem>
          <para>logdrop [to|from] <emphasis>&lt;ip address list&gt;</emphasis>
          - causes packets from the listed IP addresses to be dropped and
          logged by the firewall. Logging will occur at the level specified by
          the BLACKLIST_LOGLEVEL setting at the last [re]start (logging will
          be at the 'info' level if no BLACKLIST_LOGLEVEL was given).</para>
        </listitem>

        <listitem>
          <para>logreject [to|from}<emphasis>&lt;ip address
          list&gt;</emphasis> - causes packets from the listed IP addresses to
          be rejected and logged by the firewall. Logging will occur at the
          level specified by the BLACKLIST_LOGLEVEL setting at the last
          [re]start (logging will be at the 'info' level if no
          BLACKLIST_LOGLEVEL was given).</para>
        </listitem>
      </itemizedlist>

      <para>Dynamic blacklisting is not dependent on the
      <quote>blacklist</quote> option in
      <filename>/etc/shorewall/interfaces</filename>.</para>

      <example id="Ignore">
        <title>Ignore packets from a pair of systems</title>

        <programlisting>    <command>shorewall[-lite] drop 192.0.2.124 192.0.2.125</command></programlisting>

        <para>Drops packets from hosts 192.0.2.124 and 192.0.2.125</para>
      </example>

      <example id="Allow">
        <title>Re-enable packets from a system</title>

        <programlisting>    <command>shorewall[-lite] allow 192.0.2.125</command></programlisting>

        <para>Re-enables traffic from 192.0.2.125.</para>
      </example>

      <example>
        <title>Displaying the Dynamic Blacklist</title>

        <programlisting>    <command>shorewall show dynamic</command></programlisting>

        <para>Displays the 'dynamic' chain which contains rules for the
        dynamic blacklist. The <firstterm>source</firstterm> column contains
        the set of blacklisted addresses.</para>
      </example>
    </section>
  </section>
</article>