forked from extern/shorewall_code
025e97c8bb
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@8670 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
414 lines
18 KiB
XML
414 lines
18 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
|
|
<article id="usefull_links">
|
|
<!--$Id$-->
|
|
|
|
<articleinfo>
|
|
<title>Introduction</title>
|
|
|
|
<author>
|
|
<firstname>Tom</firstname>
|
|
|
|
<surname>Eastep</surname>
|
|
</author>
|
|
|
|
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
|
|
|
|
<copyright>
|
|
<year>2003-2007</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 type="" url="Copyright.htm">GNU Free Documentation
|
|
License</ulink></quote>.</para>
|
|
</legalnotice>
|
|
</articleinfo>
|
|
|
|
<section id="Intro">
|
|
<title>Introduction</title>
|
|
|
|
<para>The information in this document applies only to 4.x releases of
|
|
Shorewall.</para>
|
|
|
|
<section id="Glossary">
|
|
<title>Glossary</title>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><ulink url="http://www.netfilter.org">Netfilter</ulink> - the
|
|
packet filter facility builtinto the 2.4 and later Linux
|
|
kernels.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>ipchains - the packet filter facility builtinto the 2.2 Linux
|
|
kernels. Also the name of the utility program used to configure and
|
|
control that facility. Netfilter can be used in ipchains
|
|
compatibility mode.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>iptables - the utility program used to configure and control
|
|
Netfilter. The term <quote>iptables</quote> is often used to refer
|
|
to the combination of iptables+Netfilter (with Netfilter not in
|
|
ipchains compatibility mode).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>iptables-restore - a program included with iptables that
|
|
allows for atomic installation of a set of Netfilter rules. This is
|
|
a much more efficient way to install a rule set than running the
|
|
iptables utility once for each rule in the rule set.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>ifconfig - An obsolete program included in the net-utils
|
|
package. ifconfig was used to configure network interfaces.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>route - An obsolete program included in the net-utils package.
|
|
route was used to configure routing.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>ip - A program included in the iproute2 package. ip replaces
|
|
ifconfig and route in modern Linux systems.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>tc - A program included in the iproute2 package. tc is used to
|
|
configure QOS/Traffic Shaping on Linux systems.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section id="Shorewall">
|
|
<title>What is Shorewall?</title>
|
|
|
|
<para>The Shoreline Firewall, more commonly known as
|
|
<quote>Shorewall</quote>, is high-level tool for configuring Netfilter.
|
|
You describe your firewall/gateway requirements using entries in a set
|
|
of configuration files. Shorewall reads those configuration files and
|
|
with the help of the iptables, iptables-restore, ip and tc utilities,
|
|
Shorewall configures Netfilter and the Linux networking subsystem to
|
|
match your requirements. Shorewall can be used on a dedicated firewall
|
|
system, a multi-function gateway/router/server or on a standalone
|
|
GNU/Linux system. Shorewall does not use Netfilter's ipchains
|
|
compatibility mode and can thus take advantage of Netfilter's connection
|
|
state tracking capabilities.</para>
|
|
|
|
<para>Shorewall is not a daemon. Once Shorewall has configured the Linux
|
|
networking subsystem, its job is complete and there is no
|
|
<quote>Shorewall process</quote> left running in your system. The <ulink
|
|
url="starting_and_stopping_shorewall.htm">/sbin/shorewall program can be
|
|
used at any time to monitor the Netfilter firewall</ulink>.</para>
|
|
|
|
<para>Shorewall is not the easiest to use of the available iptables
|
|
configuration tools but I believe that it is the most flexible and
|
|
powerful. So if you are looking for a simple point-and-click
|
|
set-and-forget Linux firewall solution that requires a minimum of
|
|
networking knowledge, I would encourage you to check out the following
|
|
alternatives:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><ulink
|
|
url="http://www.m0n0.ch/wall/">http://www.m0n0.ch/wall/</ulink></para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><ulink
|
|
url="http://www.fs-security.com/">http://www.fs-security.com/</ulink></para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>If you are looking for a Linux firewall solution that can handle
|
|
complex and fast changing network environments then Shorewall is a
|
|
logical choice.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="Concepts">
|
|
<title>Shorewall Concepts</title>
|
|
|
|
<para>The configuration files for Shorewall are contained in the directory
|
|
<filename class="directory">/etc/shorewall</filename> -- for simple
|
|
setups, you will only need to deal with a few of them.</para>
|
|
|
|
<para>Shorewall views the network where it is running as being composed of
|
|
a set of <firstterm>zones</firstterm>. In the <ulink
|
|
url="three-interface.htm">three-interface sample configuration</ulink> for
|
|
example, the following zone names are used:</para>
|
|
|
|
<programlisting>#NAME DESCRIPTION
|
|
fw The firewall itself
|
|
net The Internet
|
|
loc Your Local Network
|
|
dmz Demilitarized Zone</programlisting>
|
|
|
|
<para>Zones are declared and given a type in the <ulink
|
|
url="manpages/shorewall-zones.html"><filename
|
|
class="directory">/etc/shorewall/</filename><filename>zones</filename></ulink>
|
|
file.Here is the <ulink url="manpages/shorewall-zones.html"><filename
|
|
class="directory">/etc/shorewall/</filename><filename>zones</filename></ulink>
|
|
file from the three-interface sample:</para>
|
|
|
|
<programlisting>#ZONE TYPE OPTIONS IN OUT
|
|
# OPTIONS OPTIONS
|
|
fw firewall
|
|
net ipv4
|
|
loc ipv4
|
|
dmz ipv4
|
|
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE</programlisting>
|
|
|
|
<para>Note that Shorewall recognizes the firewall system as its own zone.
|
|
The name of the zone designating the firewall itself (usually 'fw' as
|
|
shown in the above file) is stored in the shell variable
|
|
$<firstterm>FW</firstterm> which may be used throughout the Shorewall
|
|
configuration to refer to the firewall zone.</para>
|
|
|
|
<para>The simplest way to define the hosts in a zone is to associate the
|
|
zone with a network interface using the <ulink
|
|
url="manpages/shorewall-interfaces.html"><filename>/etc/shorewall/interfaces</filename></ulink>
|
|
file. In the three-interface sample, the three zones are defined using
|
|
that file as follows:</para>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
net eth0 detect dhcp,routefilter,norfc1918
|
|
loc eth1 detect
|
|
dmz eth2 detect</programlisting>
|
|
|
|
<para>The above file defines the <emphasis>net</emphasis> zone as all IPv4
|
|
hosts interfacing to the firewall through eth0, the
|
|
<emphasis>loc</emphasis> zone as all IPv4 hosts interfacing through eth1
|
|
and the <emphasis>dmz</emphasis> as all IPv4 hosts interfacing through
|
|
eth2. It is important to note that the composition of a zone is defined in
|
|
terms of a combination of addresses <emphasis role="bold">and</emphasis>
|
|
interfaces. When using the <ulink
|
|
url="manpages/shorewall-interfaces.html"><filename>/etc/shorewall/interfaces</filename></ulink>
|
|
file to define a zone, all addresses are included; when you want to define
|
|
a zone that contains a limited subset of the IPv4 address space, you use
|
|
the <ulink
|
|
url="manpages/shorewall-hosts.html"><filename>/etc/shorewall/hosts</filename></ulink>
|
|
file.</para>
|
|
|
|
<para>Rules about what traffic to allow and what traffic to deny are
|
|
expressed in terms of zones. <itemizedlist spacing="compact">
|
|
<listitem>
|
|
<para>You express your default policy for connections from one zone
|
|
to another zone in the <ulink
|
|
url="manpages/shorewall-policy.html"><filename
|
|
class="directory">/etc/shorewall/</filename><filename>policy</filename></ulink>
|
|
file. The basic choices for policy are:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>ACCEPT - Accept the connection.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>DROP - Ignore the connection request.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>REJECT - Return an appropriate error to the connection
|
|
request.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>Connection request logging may be specified as part of a
|
|
policy and it is conventional (and highly recommended) to log DROP
|
|
and REJECT policies.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>You define exceptions to these default policies in the <ulink
|
|
url="manpages/shorewall-rules.html"><filename
|
|
class="directory">/etc/shorewall/</filename><filename>rules</filename></ulink>
|
|
file.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>You only need concern yourself with connection requests. You
|
|
don't need to define rules for handling traffic that is part of an
|
|
established connection is and in most cases you don't have to worry
|
|
about how related connections are handled (ICMP error packets and
|
|
<ulink url="FTP.html">related TCP connection requests such as used
|
|
by FTP</ulink>).</para>
|
|
</listitem>
|
|
</itemizedlist>For each connection request entering the firewall, the
|
|
request is first checked against the <filename
|
|
class="directory">/etc/shorewall/</filename><filename>rules</filename>
|
|
file. If no rule in that file matches the connection request then the
|
|
first policy in <filename
|
|
class="directory">/etc/shorewall/</filename><filename>policy</filename>
|
|
that matches the request is applied. If there is a default action defined
|
|
for the policy in /etc/shorewall/actions (or
|
|
<filename>/usr/share/shorewall/actions.std</filename>) then that action is
|
|
invoked before the policy is enforced. In the standard Shorewall
|
|
distribution, the DROP policy has a default action called <emphasis
|
|
role="bold">Drop</emphasis> and the REJECT policy has a default action
|
|
called <emphasis role="bold">Reject</emphasis>. Default actions are used
|
|
primarily to discard packets silently so that they don't clutter up your
|
|
log.</para>
|
|
|
|
<para>The <filename
|
|
class="directory">/etc/shorewall/</filename><filename>policy</filename>
|
|
file included with the three-interface sample has the following policies:
|
|
<programlisting>#SOURCE DEST POLICY LOG LEVEL LIMIT:BURST
|
|
loc net ACCEPT
|
|
net all DROP info
|
|
all all REJECT info</programlisting>In the three-interface
|
|
sample, the line below is included but commented out. If you want your
|
|
firewall system to have full access to servers on the Internet, uncomment
|
|
that line. <programlisting>#SOURCE DEST POLICY LOG LEVEL LIMIT:BURST
|
|
$FW net ACCEPT</programlisting> The above policy will:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Allow all connection requests from your local network to the
|
|
Internet</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Drop (ignore) all connection requests from the Internet to
|
|
your firewall or local networks; these ignored connection requests
|
|
will be logged using the <emphasis>info</emphasis> syslog priority
|
|
(log level).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Optionally accept all connection requests from the firewall to
|
|
the Internet (if you uncomment the additional policy)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>reject all other connection requests; these rejected
|
|
connection requests will be logged using the
|
|
<emphasis>info</emphasis> syslog priority (log level).</para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
|
|
<para>To illustrate how rules provide exceptions to policies, suppose that
|
|
you have the polices listed above but you want to be able to connect to
|
|
your firewall from the Internet using Secure Shell (SSH). Recall that SSH
|
|
connects uses TCP port 22.</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DEST
|
|
# PORT(S)
|
|
ACCEPT net $FW tcp 22</programlisting>
|
|
|
|
<para>So although you have a policy of ignoring all connection attempts
|
|
from the net zone (from the Internet), the above exception to that policy
|
|
allows you to connect to the SSH server running on your firewall.</para>
|
|
|
|
<para>Because Shorewall makes no assumptions about what traffic you want
|
|
accepted, there are certain rules (exceptions) that need to be added to
|
|
almost any configuration.</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>The <ulink url="shorewall_quickstart_guide.htm">QuickStart
|
|
guides</ulink> point to pre-populated files for use in common setups
|
|
and the <ulink url="shorewall_setup_guide.htm">Shorewall Setup
|
|
Guide</ulink> shows you examples for use with other more complex
|
|
setups.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>To keep your <ulink url="shorewall_logging.html">firewall
|
|
log</ulink> from filling up with useless noise, Shorewall provides
|
|
<ulink url="Actions.html">common actions</ulink> that silently discard
|
|
or reject such noise before it can be logged. As with everything in
|
|
Shorewall, you can alter the behavior of these common actions (or do
|
|
away with them entirely) as you see fit.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section id="Compile">
|
|
<title>Compile then Execute</title>
|
|
|
|
<para>Shorewall versions beginning with 3.2.0 use a "compile" then
|
|
"execute" approach. The Shorewall configuration compiler reads the
|
|
configuration files and generates a shell script. Errors in the
|
|
compilation step cause the script to be discarded and the command to be
|
|
aborted. If the compilation step doesn't find any errors then the shell
|
|
script is executed.</para>
|
|
|
|
<para>The 'compiled' scripts are placed in the directory <filename
|
|
class="directory">/var/lib/shorewall</filename> and are named to
|
|
correspond to the command being executed. For example, the command
|
|
"/sbin/shorewall start" will generate a script named
|
|
<filename>/var/lib/shorewall/.start</filename> and, if the compilation is
|
|
error free, that script will then be executed.</para>
|
|
</section>
|
|
|
|
<section id="Packages">
|
|
<title>Shorewall Packages</title>
|
|
|
|
<para>Shorewall 4.0 consists of four packages.</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para><emphasis role="bold">Shorewall-common</emphasis>. This package
|
|
must be installed on at least one system in your network. That system
|
|
must also have Shorewall-shell and/or Shorewall-perl installed.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Shorewall-shell</emphasis>. This package
|
|
includes the legacy Shorewall configuration compiler written in Bourne
|
|
Shell. This compiler is very portable but suffers from performance
|
|
problems and has become hard to maintain.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Shorewall-perl</emphasis>. An alternative
|
|
to Shorewall-shell written in the Perl language. This compiler is
|
|
highly portable to those Unix-like platforms that support Perl
|
|
(including Cygwin) and is the compiler of choice for new Shorewall
|
|
installations. Scripts created using Shorewall-perl use
|
|
iptables-restore to install the generated Netfilter rule set.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Shorewall-lite</emphasis>. Shorewall
|
|
allows for central administration of multiple firewalls through use of
|
|
Shorewall lite. The full Shorewall product (along with Shorewall-shell
|
|
and/or Shorewall-perl) are installed on a central administrative
|
|
system where compiled Shorewall scripts are generated. These scripts
|
|
are copied to the firewall systems where they run under the control of
|
|
Shorewall-lite.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
</section>
|
|
|
|
<section id="License">
|
|
<title>License</title>
|
|
|
|
<para>This program is free software; you can redistribute it and/or modify
|
|
it under the terms of <ulink
|
|
url="http://www.gnu.org/licenses/gpl.html">Version 2 of the GNU General
|
|
Public License</ulink> as published by the Free Software
|
|
Foundation.</para>
|
|
|
|
<para>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 detail.</para>
|
|
|
|
<para>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.</para>
|
|
</section>
|
|
</article>
|