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shorewall_code/Shorewall-docs2/blacklisting_support.xml
2005-08-28 23:37:51 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Shorewall Blacklisting Support</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate>2005-08-28</pubdate>
<copyright>
<year>2002-2005</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>Introduction</title>
<para>Shorewall supports two different forms of blacklisting; static and
dynamic. The BLACKLISTNEWONLY option in /etc/shorewall/shorewall.conf
controls the degree of blacklist filtering:</para>
<orderedlist>
<listitem>
<para>BLACKLISTNEWONLY=No --&nbsp; 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. Only the source address is checked against the
blacklists.</para>
</listitem>
</orderedlist>
<important>
<para><emphasis role="bold">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>
</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>
<section>
<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="Documentation.htm#Config"><filename>/etc/shorewall/shorewall.conf</filename>.</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="Documentation.htm#Config"><filename>/etc/shorewall/shorewall.conf</filename></ulink>.</para>
</listitem>
<listitem>
<para>You list the IP addresses/subnets that you wish to blacklist in
<ulink
url="Documentation.htm#Blacklist"><filename>/etc/shorewall/blacklist</filename></ulink>.
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="Documentation.htm#Interfaces"><filename>/etc/shorewall/interfaces</filename></ulink>.</para>
</listitem>
<listitem>
<para>The black list is refreshed from
<filename>/etc/shorewall/blacklist</filename> by the <quote><ulink
url="starting_and_stopping_shorewall.htm"><command>shorewall
refresh</command></ulink></quote> command.</para>
</listitem>
</itemizedlist>
<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 ipsec. 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>
<title>Dynamic Blacklisting</title>
<para>Dynamic blacklisting doesn't use any configuration parameters but is
rather controlled using /sbin/shorewall commands:</para>
<itemizedlist>
<listitem>
<para>drop <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 <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 <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>
</listitem>
<listitem>
<para>show dynamic - displays the dynamic blacklisting
configuration.</para>
</listitem>
</itemizedlist>
<para>Dynamic blacklisting is not dependent on the
<quote>blacklist</quote> option in
<filename>/etc/shorewall/interfaces</filename>.</para>
<example>
<title>Ignore packets from a pair of systems</title>
<programlisting> <command>shorewall 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>
<title>Re-enable packets from a system</title>
<programlisting> <command>shorewall allow 192.0.2.125</command></programlisting>
<para>Re-enables traffic from 192.0.2.125.</para>
</example>
</section>
</article>