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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>Compiled Firewall Programs and Shorewall Lite</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2006-2007</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 4.0 and
later. If you are running a version of Shorewall earlier than Shorewall
4.0.0-Beta4 or you are not running Shorewall-perl then please see <ulink
url="3.0/NewBridge.html">this article</ulink>.</emphasis></para>
</caution>
<section id="Overview">
<title>Overview</title>
<para>Beginning with Shorewall version 3.1, Shorewall has the capability
to compile a Shorewall configuration and produce a runnable firewall
program script. The script is a complete program which can be placed on a
system with <emphasis>Shorewall Lite</emphasis> installed and can serve as
the firewall creation script for that system.</para>
<section id="Restrictions">
<title>Restrictions</title>
<para>While compiled Shorewall programs are useful in many cases, there
are some important restrictions that you should be aware of before
attempting to use them.</para>
<orderedlist>
<listitem>
<para>The <emphasis role="bold">detectnets</emphasis> interface
option is not supported.</para>
</listitem>
<listitem>
<para>DYNAMIC_ZONES=Yes in <filename>shorewall.conf</filename> is
not supported.</para>
</listitem>
<listitem>
<para>All extension scripts used are copied into the program (with
the exception of <ulink url="shorewall_extension_scripts.htm">those
executed a compile-time by Shorewall-perl</ulink>). The
ramifications of this are:</para>
<itemizedlist>
<listitem>
<para>If you update an extension script, the compiled program
will not use the updated script.</para>
</listitem>
<listitem>
<para>Beginning with Shorewall 3.2.9 and 3.4.0 RC2, the
<filename>params</filename> file is only processed at compile
time if you set EXPORTPARAMS=No in
<filename>shorewall.conf</filename>. For run-time setting of
shell variables, use the <filename>init</filename> extension
script. Although the default setting is EXPORTPARAMS=Yes for
compatibility, the recommended setting is
EXPORTPARAMS=No.</para>
<para>If the <filename>params</filename> file needs to set shell
variables based on the configuration of the firewall system, you
can use this trick:</para>
<programlisting>EXT_IP=$(ssh root@firewall "/sbin/shorewall-lite call find_first_interface_address eth0")</programlisting>
<para>The <command>shorewall-lite call</command> command allows
you to to call interactively any Shorewall function that you can
call in an extension script.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>You must install Shorewall Lite on the system where you want
to run the script. You then install the compiled program in
/usr/share/shorewall-lite/firewall and use the /sbin/shorewall-lite
program included with Shorewall Lite to control the firewall just as
if the full Shorewall distribution was installed.</para>
</listitem>
</orderedlist>
</section>
</section>
<section id="Compile">
<title>The "shorewall compile" command</title>
<para>A compiled script is produced using the <command>compile</command>
command:</para>
<blockquote>
<para><command>shorewall compile [ -e ] [ C {perl|shell} ] [
&lt;directory name&gt; ] &lt;path name&gt;</command></para>
</blockquote>
<para>where</para>
<blockquote>
<variablelist>
<varlistentry>
<term>-e</term>
<listitem>
<para>Indicates that the program is to be "exported" to another
system. When this flag is set, neither the "detectnets" interface
option nor DYNAMIC_ZONES=Yes in shorewall.conf are allowed. The
created program may be run on a system that has only Shorewall
Lite installed</para>
<para>When this flag is given, Shorewall does not probe the
current system to determine the kernel/iptables features that it
supports. It rather reads those capabilities from
<filename>/etc/shorewall/capabilities</filename>. See below for
details.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>-C {perl|shell}</term>
<listitem>
<para>Specifies the compiler to use. Overrides the
SHOREWALL_COMPILER setting in <ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>&lt;directory name&gt;</term>
<listitem>
<para>specifies a directory to be searched for configuration files
before those directories listed in the CONFIG_PATH variable in
<filename>shorewall.conf</filename>.</para>
<para>When -e &lt;directory-name&gt; is included, only the
SHOREWALL_SHELL and VERBOSITY settings from
<filename>/etc/shorewall/shorewall.conf</filename> are used and
these apply only to the compiler itself. The settings used by the
compiled firewall script are determined by the contents of
<filename>&lt;directory name&gt;/shorewall.conf</filename>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>&lt;path name&gt;</term>
<listitem>
<para>specifies the name of the script to be created.</para>
</listitem>
</varlistentry>
</variablelist>
</blockquote>
</section>
<section id="Lite">
<title>Shorewall Lite (Added in version 3.2.0 RC 1)</title>
<para>Shorewall Lite is a companion product to Shorewall and is designed
to allow you to maintain all Shorewall configuration information on a
single system within your network.</para>
<orderedlist numeration="loweralpha">
<listitem>
<para>You install the full Shorewall release on one system within your
network. You need not configure Shorewall there and you may totally
disable startup of Shorewall in your init scripts. For ease of
reference, we call this system the 'administrative system'.</para>
<caution>
<para>If you want to be able to allow non-root users to manage
remote firewall systems, then the files
<filename>/etc/shorewall/params</filename> and
<filename>/etc/shorewall/shorewall.conf</filename> must be readable
by all users on the administrative system. Not all packages secure
the files that way and you may have to change the file permissions
yourself. /sbin/shorewall uses the SHOREWALL_COMPILER setting to
determine which compiler to launch. If the compiler is
shorewall-shell, then the SHOREWALL_SHELL setting from
<filename>/etc/shorewall/shorewall.conf</filename> determines the
shell to use. /sbin/shorewall also uses the VERBOSITY setting for
determining how much output the compiler generates. All other
settings are taken from the <filename>shorewall.conf </filename>file
in the remote systems <firstterm>export directory</firstterm> (see
below).</para>
</caution>
</listitem>
<listitem>
<para>On each system where you wish to run a Shorewall-generated
firewall, you install Shorewall Lite. For ease of reference, we will
call these systems the 'firewall systems'.</para>
<note>
<para>The firewall systems do <emphasis role="bold">NOT</emphasis>
need to have the full Shorewall product installed but rather only
the Shorewall Lite product. Shorewall and Shorewall LIte may be
installed on the same system but that isn't encouraged.</para>
</note>
</listitem>
<listitem>
<para>On the administrative system you create a separate 'export
directory' for each firewall system. You copy the contents of
/usr/share/shorewall/configfiles into each export directory.</para>
</listitem>
<listitem>
<para>If you are running Shorewall 3.2.5 or earlier, then on each
firewall system, you run:</para>
<programlisting><command>/usr/share/shorewall-lite/shorecap &gt; capabilities</command>
<command>scp capabilities &lt;admin system&gt;:&lt;this system's config dir&gt;</command></programlisting>
<para>If you are running Debian or one of its derivatives like Ubuntu
then edit /etc/default/shorewall-lite and set startup=1.</para>
</listitem>
<listitem>
<para>On the administrative system, for each firewall system you do
the following (this may be done by a non-root user who has root ssh
access to the firewall system):</para>
<orderedlist>
<listitem>
<para>modify the files in the corresponding export directory
appropriately. It's a good idea to include the IP address of the
administrative system in the <filename>routestopped</filename>
file.</para>
<para>It is important to understand that with Shorewall Lite, the
firewall's export directory on the administrative system acts as
<filename class="directory">/etc/shorewall</filename> for that
firewall. So when the Shorewall documentation gives instructions
for placing entries in files in the firewall's <filename
class="directory">/etc/shorewall</filename>, when using Shorewall
Lite you make those changes in the firewall's export directory on
the administrative system.</para>
<para>The CONFIG_PATH variable is treated as follows:</para>
<itemizedlist>
<listitem>
<para>The value of CONFIG_PATH in
<filename>/etc/shorewall/shorewall.conf </filename>is ignored
when compiling for export (the -e option in given) and when
the <command>load</command> or <command>reload</command>
command is being executed (see below).</para>
</listitem>
<listitem>
<para>The value of CONFIG_PATH in the
<filename>shorewall.conf</filename> file in the export
directory is used to search for configuration files during
compilation of that configuration.</para>
</listitem>
<listitem>
<para>The value of CONFIG_PATH used when the script is run on
the firewall system is
"/etc/shorewall-lite:/usr/share/shorewall-lite".</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<programlisting><command>cd &lt;export directory&gt;</command>
<command>/sbin/shorewall load -c firewall</command></programlisting>
<para>The <ulink
url="starting_and_stopping_shorewall.htm#Load"><command>load</command></ulink>
command compiles a firewall script from the configuration files in
the current working directory (using <command>shorewall compile
-e</command>), copies that file to the remote system via scp and
starts Shorewall Lite on the remote system via ssh. The -c option
causes the capabilities of the remote system to be generated and
copied to a file named capabilities in the export directory. See
<link linkend="Shorecap">below</link>.</para>
<para>Example (firewall's DNS name is 'gateway'):</para>
<para><command>/sbin/shorewall load -c gateway</command></para>
</listitem>
</orderedlist>
</listitem>
<listitem>
<para>If you later need to change the firewall's configuration, change
the appropriate files in the firewall's export directory then:</para>
<programlisting><command>cd &lt;export directory&gt;</command>
<command>/sbin/shorewall reload firewall</command></programlisting>
<para>The <ulink
url="manpages/shorewall.html"><command>reload</command></ulink>
command compiles a firewall script from the configuration files in the
current working directory (using <command>shorewall compile
-e</command>), copies that file to the remote system via scp and
restarts Shorewall Lite on the remote system via ssh. Note: In
Shorewall 3.2.6 and later, the <emphasis role="bold">reload</emphasis>
command also supports the '-c' option.</para>
<para>I personally place a <filename>Makefile</filename> in each
export directory as follows:</para>
<blockquote>
<programlisting># Shorewall Packet Filtering Firewall Export Directory Makefile - V3.3
#
# This program is under GPL [http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt]
#
# (c) 2006 - Tom Eastep (teastep@shorewall.net)
#
# Shorewall documentation is available at http://www.shorewall.net
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of Version 2 of the GNU General Public License
# as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
################################################################################
# Place this file in each export directory. Modify each copy to set HOST
# to the name of the remote firewall corresponding to the directory.
#
# To make the 'firewall' script, type "make".
#
# Once the script is compiling correctly, you can install it by
# typing "make install".
#
################################################################################
# V A R I A B L E S
#
# Files in the export directory on which the firewall script does not depend
#
IGNOREFILES = firewall% Makefile% trace% %~
#
# Remote Firewall system
#
HOST = gateway
#
# Save some typing
#
LITEDIR = /var/lib/shorewall-lite
#
# Set this if the remote system has a non-standard modules directory
#
MODULESDIR=
#
# Default target is the firewall script
#
################################################################################
# T A R G E T S
#
all: firewall
#
# Only generate the capabilities file if it doesn't already exist
#
capabilities:
ssh root@$(HOST) "MODULESDIR=$(MODULESDIR) /usr/share/shorewall-lite/shorecap &gt; $(LITEDIR)/capabilities"
scp root@$(HOST):$(LITEDIR)/capabilities .
#
# Compile the firewall script. Using the 'wildcard' function causes "*" to be expanded so that
# 'filter-out' will be presented with the list of files in this directory rather than "*"
#
firewall: $(filter-out $(IGNOREFILES) capabilities , $(wildcard *) ) capabilities
shorewall compile -e . firewall
#
# Only reload on demand.
#
install: firewall
scp firewall firewall.conf root@$(HOST):$(LITEDIR)
ssh root@$(HOST) "/sbin/shorewall-lite restart"
#
# Save running configuration
#
save:
ssh root@$(HOST) "/sbin/shorewall-lite save"
#
# Remove generated files
#
clean:
rm -f capabilities firewall firewall.conf reload
</programlisting>
</blockquote>
<para>That way, after I've changed the configuration, I can simply
type <command>make</command> or <emphasis role="bold">make
install</emphasis>.</para>
<note>
<para>The above Makefile is available at <ulink
url="http://www1.shorewall.net/pub/shorewall/contrib/Shorewall-lite/">http://www.shorewall.net/pub/shorewall/contrib/Shorewall-lite/</ulink></para>
</note>
<note>
<para>I omit trace% because I often trace compiler execution while
I'm debugging new versions of Shorewall.</para>
</note>
</listitem>
</orderedlist>
<para>There is a <filename>shorewall-lite.conf</filename> file installed
as part of Shorewall Lite
(<filename>/etc/shorewall-lite/shorewall-lite.conf</filename>). You can
use that file on the firewall system to override some of the settings from
the shorewall.conf file in the export directory.</para>
<para>Settings that you can override are:</para>
<blockquote>
<simplelist>
<member>VERBOSITY</member>
<member>LOGFILE</member>
<member>LOGFORMAT</member>
<member>IPTABLES</member>
<member>PATH</member>
<member>SHOREWALL_SHELL</member>
<member>SUBSYSLOCK</member>
<member>RESTOREFILE</member>
</simplelist>
</blockquote>
<para>You will normally not need to touch
<filename>/etc/shorewall-lite/shorewall-lite.conf</filename>.</para>
<para>The <filename>/sbin/shorewall-lite</filename> program included with
Shorewall Lite supports the same set of commands as the
<filename>/sbin/shorewall</filename> program in a full Shorewall
installation with the following exceptions:</para>
<blockquote>
<simplelist>
<member>add</member>
<member>compile</member>
<member>delete</member>
<member>refresh</member>
<member>reload</member>
<member>try</member>
<member>safe-start</member>
<member>safe-restart</member>
<member>show actions</member>
<member>show macros</member>
</simplelist>
</blockquote>
<para>On systems with only Shorewall Lite installed, I recommend that you
create a symbolic link <filename>/sbin/shorewall</filename> and point it
at <filename>/sbin/shorewall-lite</filename>. That way, you can use
<command>shorewall</command> as the command regardless of which product is
installed.</para>
<blockquote>
<programlisting><command>ln -sf shorewall-lite /sbin/shorewall</command></programlisting>
</blockquote>
<section id="Converting">
<title>Converting a system from Shorewall to Shorewall Lite</title>
<para>Converting a firewall system that is currently running Shorewall
to run Shorewall Lite instead is straight-forward.</para>
<orderedlist numeration="loweralpha">
<listitem>
<para>On the administrative system, create an export directory for
the firewall system.</para>
</listitem>
<listitem>
<para>Copy the contents of <filename
class="directory">/etc/shorewall/</filename> from the firewall
system to the export directory on the administrative system.</para>
</listitem>
<listitem>
<para>On the firewall system:</para>
<para>Be sure that the IP address of the administrative system is
included in <filename>/etc/shorewall/routestopped</filename>.</para>
<programlisting><command>shorewall stop</command></programlisting>
<para><emphasis role="bold">We recommend that you uninstall
Shorewall at this point.</emphasis></para>
</listitem>
<listitem>
<para>Install Shorewall Lite on the firewall system.</para>
<para>If you are running Debian or one of its derivatives like
Ubuntu then edit /etc/default/shorewall-lite and set
startup=1.</para>
</listitem>
<listitem>
<para>On the administrative system:</para>
<para>It's a good idea to include the IP address of the
administrative system in the firewall system's
<filename>routestopped</filename> file.</para>
<para>Also, edit the shorewall.conf file in the firewall's export
directory and change the CONFIG_PATH setting to remove <filename
class="directory">/etc/shorewall</filename>. You can replace it with
<filename
class="directory">/usr/share/shorewall/configfiles</filename> if you
like.</para>
<para>Example:</para>
<blockquote>
<para>Before editing:</para>
<programlisting>CONFIG_PATH=/etc/shorewall:/usr/share/shorewall</programlisting>
<para>After editing:</para>
<programlisting>CONFIG_PATH=/usr/share/shorewall/configfiles:/usr/share/shorewall</programlisting>
</blockquote>
<para>Changing CONFIG_PATH will ensure that subsequent compilations
using the export directory will not include any files from <filename
class="directory">/etc/shorewall</filename>.</para>
<para>If you set variables in the params file, there are a couple of
issues:</para>
<para>Beginning with Shorewall 3.2.9 and 3.4.0 RC2, the
<filename>params</filename> file is only processed at compile time
if you set EXPORTPARAMS=No in <filename>shorewall.conf</filename>.
For run-time setting of shell variables, use the
<filename>init</filename> extension script.</para>
<para>If the <filename>params</filename> file needs to set shell
variables based on the configuration of the firewall system, you can
use this trick:</para>
<programlisting>EXT_IP=$(ssh root@firewall "/sbin/shorewall-lite call find_first_interface_address eth0")</programlisting>
<para>The <command>shorewall-lite call</command> command allows you
to to call interactively any Shorewall function that you can call in
an extension script.</para>
<para>After having made the above changes to the firewall's export
directory, execute the following commands.</para>
<blockquote>
<programlisting><command>cd &lt;export directory&gt;</command>
<command>/sbin/shorewall load -c &lt;firewall system&gt;</command>
</programlisting>
<para>Example (firewall's DNS name is 'gateway'):</para>
<para><command>/sbin/shorewall load -c gateway</command></para>
</blockquote>
<para>The <ulink
url="starting_and_stopping_shorewall.htm#Load"><command>load</command></ulink>
command compiles a firewall script from the configuration files in
the current working directory (using <command>shorewall compile
-e</command>), copies that file to the remote system via scp and
starts Shorewall Lite on the remote system via ssh.</para>
</listitem>
<listitem>
<para>If you later need to change the firewall's configuration,
change the appropriate files in the firewall's export directory
then:</para>
<programlisting><command>cd &lt;export directory&gt;</command>
<command>/sbin/shorewall reload firewall</command></programlisting>
<para>The <ulink
url="starting_and_stopping_shorewall.htm#Reload"><command>reload</command></ulink>
command compiles a firewall script from the configuration files in
the current working directory (using <command>shorewall compile
-e</command>), copies that file to the remote system via scp and
restarts Shorewall Lite on the remote system via ssh.</para>
</listitem>
<listitem>
<para>If the kernel/iptables configuration on the firewall later
changes and you need to create a new capabilities file, do the
following:</para>
<programlisting><command>/usr/share/shorewall-lite/shorecap &gt; capabilities</command>
<command>scp capabilities &lt;admin system&gt;:&lt;this system's config dir&gt;</command></programlisting>
<para>Or, if you are running Shorewall 3.2.6 or later, simply use
the -c option the next time that you use the
<command>reload</command> command.</para>
</listitem>
</orderedlist>
</section>
</section>
<section id="Shorecap">
<title>The /etc/shorewall/capabilities file and the shorecap
program</title>
<para>As mentioned above, the /etc/shorewall/capabilities file specifies
that kernel/iptables capabilities of the target system. Here is a sample
file:</para>
<blockquote>
<programlisting>#
# Shorewall detected the following iptables/netfilter capabilities - Fri Jul 27 14:22:31 PDT 2007
#
NAT_ENABLED=Yes
MANGLE_ENABLED=Yes
MULTIPORT=Yes
XMULTIPORT=Yes
CONNTRACK_MATCH=Yes
USEPKTTYPE=Yes
POLICY_MATCH=Yes
PHYSDEV_MATCH=Yes
LENGTH_MATCH=Yes
IPRANGE_MATCH=Yes
RECENT_MATCH=Yes
OWNER_MATCH=Yes
IPSET_MATCH=
CONNMARK=Yes
XCONNMARK=Yes
CONNMARK_MATCH=Yes
XCONNMARK_MATCH=Yes
RAW_TABLE=Yes
IPP2P_MATCH=
CLASSIFY_TARGET=Yes
ENHANCED_REJECT=Yes
KLUDGEFREE=Yes
MARK=Yes
XMARK=Yes
MANGLE_FORWARD=Yes
COMMENTS=Yes
ADDRTYPE=Yes
CAPVERSION=30405</programlisting>
</blockquote>
<para>As you can see, the file contains a simple list of shell variable
assignments — the variables correspond to the capabilities listed by the
<command>shorewall show capabilities</command> command and they appear in
the same order as the output of that command.</para>
<para>To aid in creating this file, Shorewall Lite includes a
<command>shorecap</command> program. The program is installed in the
<filename>/usr/share/shorewall-lite/</filename> directory and may be run
as follows:</para>
<blockquote>
<para><command>[ IPTABLES=&lt;iptables binary&gt; ] [
MODULESDIR=&lt;kernel modules directory&gt; ]
/usr/share/shorewall-lite/shorecap &gt; capabilities</command></para>
</blockquote>
<para>The IPTABLES and MODULESDIR options have their <ulink
url="manpages/shorewall.conf.html">usual Shorewall default
values</ulink>.</para>
<para>The <filename>capabilities</filename> file may then be copied to a
system with Shorewall installed and used when compiling firewall programs
to run on the remote system.</para>
<para>Beginning with Shorewall Lite version 3.2.2, the capabilities file
may also be creating using
<filename>/sbin/shorewall-lite:</filename><blockquote>
<para><command>shorewall-lite show -f capabilities &gt;
capabilities</command></para>
</blockquote></para>
<para>Note that unlike the shorecap program, the <command>show
capabilities</command> command shows the kernel's current capabilities; it
does not attempt to load additional kernel modules.</para>
</section>
<section id="Running">
<title>Running compiled programs directly</title>
<para>Compiled firewall programs are complete programs that support the
following run-line commands:</para>
<blockquote>
<simplelist>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
start</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
stop</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
clear</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
refresh</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
reset</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
restart</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
status</command></member>
<member><command>&lt;program&gt; [ -q ] [ -v ] [ -n ]
version</command></member>
</simplelist>
</blockquote>
<para>The options have their same meaning is when they are passed to
<filename>/sbin/shorewall</filename> itself. The default VERBOSITY level
is the level specified in the shorewall.conf file used when then program
was compiled.</para>
</section>
</article>