mirror of
https://gitlab.com/shorewall/code.git
synced 2024-12-15 19:01:19 +01:00
4b7193460b
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@1062 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
388 lines
16 KiB
XML
388 lines
16 KiB
XML
<?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="standalone">
|
|
<!--$Id$-->
|
|
|
|
<articleinfo>
|
|
<title>Standalone Firewall</title>
|
|
|
|
<authorgroup>
|
|
<author>
|
|
<firstname>Tom</firstname>
|
|
|
|
<surname>Eastep</surname>
|
|
</author>
|
|
</authorgroup>
|
|
|
|
<pubdate>2004-01-06</pubdate>
|
|
|
|
<copyright>
|
|
<year>2002-2004</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>Setting up Shorewall on a standalone Linux system is very easy if
|
|
you understand the basics and follow the documentation.</para>
|
|
|
|
<para>This guide doesn't attempt to acquaint you with all of the
|
|
features of Shorewall. It rather focuses on what is required to configure
|
|
Shorewall in one of its most common configurations:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Linux system</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Single external IP address</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Connection through Cable Modem, DSL, ISDN, Frame Relay,
|
|
dial-up...</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<section>
|
|
<title>Requirements</title>
|
|
|
|
<para>Shorewall requires that you have the iproute/iproute2 package
|
|
installed (on RedHat, the package is called <emphasis>iproute</emphasis>).
|
|
You can tell if this package is installed by the presence of an
|
|
<emphasis role="bold">ip</emphasis> program on your firewall system. As
|
|
root, you can use the <quote>which</quote> command to check for this
|
|
program:</para>
|
|
|
|
<programlisting>[root@gateway root]# which ip
|
|
/sbin/ip
|
|
[root@gateway root]#</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Before you start</title>
|
|
|
|
<para>I recommend that you read through the guide first to familiarize
|
|
yourself with what's involved then go back through it again making
|
|
your configuration changes.</para>
|
|
|
|
<caution>
|
|
<para>If you edit your configuration files on a Windows system, you
|
|
must save them as Unix files if your editor supports that option or
|
|
you must run them through dos2unix before trying to use them.
|
|
Similarly, if you copy a configuration file from your Windows hard
|
|
drive to a floppy disk, you must run dos2unix against the copy before
|
|
using it with Shorewall.</para>
|
|
|
|
<simplelist>
|
|
<member><ulink url="http://www.simtel.net/pub/pd/51438.html">Windows
|
|
Version of dos2unix</ulink></member>
|
|
|
|
<member><ulink url="http://www.megaloman.com/~hany/software/hd2u/">Linux
|
|
Version of dos2unix</ulink></member>
|
|
</simplelist>
|
|
</caution>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Conventions</title>
|
|
|
|
<para>Points at which configuration changes are recommended are flagged
|
|
with <inlinegraphic fileref="images/BD21298_.gif" format="GIF" />.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>PPTP/ADSL</title>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>If you have an ADSL Modem and you use PPTP to communicate with a
|
|
server in that modem, you must make the <ulink url="PPTP.htm#PPTP_ADSL">changes
|
|
recommended here</ulink> <emphasis role="underline">in addition to those
|
|
described in the steps below</emphasis>. ADSL with PPTP is most commonly
|
|
found in Europe, notably in Austria.</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Shorewall Concepts</title>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>The configuration files for Shorewall are contained in the directory
|
|
<filename class="directory">/etc/shorewall</filename> -- for simple
|
|
setups, you only need to deal with a few of these as described in this
|
|
guide. After you have <ulink url="Install.htm">installed Shorewall</ulink>,
|
|
<emphasis role="bold">download the <ulink
|
|
url="http://www1.shorewall.net/pub/shorewall/Samples/">one-interface
|
|
sample</ulink>, un-tar it (tar -zxvf one-interface.tgz) and and copy the
|
|
files to /etc/shorewall (they will replace files with the same names that
|
|
were placed in /etc/shorewall during Shorewall installation)</emphasis>.</para>
|
|
|
|
<para>As each file is introduced, I suggest that you look through the
|
|
actual file on your system -- each file contains detailed configuration
|
|
instructions and default entries.</para>
|
|
|
|
<para>Shorewall views the network where it is running as being composed of
|
|
a set of <emphasis>zones</emphasis>. In the one-interface sample
|
|
configuration, only one zone is defined:</para>
|
|
|
|
<informaltable>
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row>
|
|
<entry align="center">Name</entry>
|
|
|
|
<entry align="center">Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry>net</entry>
|
|
|
|
<entry>The Internet</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
<para>Shorewall zones are defined in <ulink url="Documentation.htm#Zones"><filename>/etc/shorewall/zones</filename></ulink>.</para>
|
|
|
|
<para>Shorewall also recognizes the firewall system as its own zone - by
|
|
default, the firewall itself is known as <emphasis role="bold">fw</emphasis>.</para>
|
|
|
|
<para>Rules about what traffic to allow and what traffic to deny are
|
|
expressed in terms of zones.</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>You express your default policy for connections from one zone to
|
|
another zone in the <ulink url="Documentation.htm#Policy"><filename>/etc/shorewall/policy</filename></ulink>
|
|
file.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>You define exceptions to those default policies in the <ulink
|
|
url="Documentation.htm#Rules"><filename>/etc/shorewall/rules</filename></ulink>
|
|
file.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>For each connection request entering the firewall, the request is
|
|
first checked against the <filename><filename>/etc/shorewall/rules</filename></filename>
|
|
file. If no rule in that file matches the connection request then the
|
|
first policy in <filename>/etc/shorewall/policy</filename> that matches
|
|
the request is applied. If that policy is REJECT or DROP the request is
|
|
first checked against the rules in /etc/shorewall/common if that file
|
|
exists; otherwise the rules in <filename>/etc/shorewall/common.def</filename>
|
|
are checked.</para>
|
|
|
|
<para>The <filename>/etc/shorewall/policy</filename> file included with
|
|
the one-interface sample has the following policies:</para>
|
|
|
|
<programlisting>#SOURCE ZONE DESTINATION ZONE POLICY LOG LEVEL LIMIT:BURST
|
|
fw net ACCEPT
|
|
net all DROP info
|
|
all all REJECT info</programlisting>
|
|
|
|
<para>The above policy will:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>allow all connection requests from the firewall to the internet</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>drop (ignore) all connection requests from the internet to your
|
|
firewall</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>reject all other connection requests (Shorewall requires this
|
|
catchall policy).</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>At this point, edit your <filename>/etc/shorewall/policy</filename>
|
|
and make any changes that you wish.</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>External Interface</title>
|
|
|
|
<para>The firewall has a single network interface. Where Internet
|
|
connectivity is through a cable or DSL <quote>Modem</quote>, the
|
|
<emphasis>External Interface</emphasis> will be the ethernet adapter (<emphasis
|
|
role="bold">eth0</emphasis>) that is connected to that <quote>Modem</quote>
|
|
<emphasis role="underline">unless</emphasis> you connect via
|
|
<emphasis>Point-to-Point Protocol over Ethernet</emphasis> (PPPoE) or
|
|
<emphasis>Point-to-Point Tunneling Protocol</emphasis> (PPTP) in which
|
|
case the External Interface will be a <emphasis role="bold">ppp0</emphasis>.
|
|
If you connect via a regular modem, your External Interface will also be
|
|
<emphasis role="bold">ppp0</emphasis>. If you connect using ISDN, your
|
|
external interface will be <emphasis role="bold">ippp0</emphasis>.</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>The Shorewall one-interface sample configuration assumes that the
|
|
external interface is <emphasis role="bold">eth0</emphasis>. If your
|
|
configuration is different, you will have to modify the sample
|
|
/etc/shorewall/interfaces file accordingly. While you are there, you may
|
|
wish to review the list of options that are specified for the interface.
|
|
Some hints:</para>
|
|
|
|
<tip>
|
|
<para>If your external interface is <emphasis role="bold">ppp0</emphasis>
|
|
or <emphasis role="bold">ippp0</emphasis>, you can replace the
|
|
<quote>detect</quote> in the second column with <quote>-</quote>.</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>If your external interface is <emphasis role="bold">ppp0</emphasis>
|
|
or <emphasis role="bold">ippp0</emphasis> or if you have a static IP
|
|
address, you can remove <quote>dhcp</quote> from the option list.</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>If you specify <emphasis>norfc1918</emphasis> for your external
|
|
interface, you will want to check the <ulink url="errata.htm">Shorewall
|
|
Errata</ulink> periodically for updates to the <filename>/etc/shorewall/rfc1918
|
|
file</filename>. Alternatively, you can <ulink url="myfiles.htm#RFC1918">strip
|
|
down your <filename>/etc/shorewall/rfc1918</filename> file as I do</ulink>.</para>
|
|
</tip>
|
|
</section>
|
|
|
|
<section>
|
|
<title>IP Addresses</title>
|
|
|
|
<para>RFC 1918 reserves several <emphasis>Private</emphasis> IP address
|
|
ranges for use in private networks:</para>
|
|
|
|
<programlisting>10.0.0.0 - 10.255.255.255
|
|
172.16.0.0 - 172.31.255.255
|
|
192.168.0.0 - 192.168.255.255</programlisting>
|
|
|
|
<para>These addresses are sometimes referred to as <emphasis>non-routable</emphasis>
|
|
because the Internet backbone routers will not forward a packet whose
|
|
destination address is reserved by RFC 1918. In some cases though, ISPs
|
|
are assigning these addresses then using <emphasis>Network Address
|
|
Translation</emphasis> to rewrite packet headers when forwarding to/from
|
|
the internet.</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>Before starting Shorewall, you should look at the IP address of your
|
|
external interface and if it is one of the above ranges, you should remove
|
|
the <quote>norfc1918</quote> option from the entry in
|
|
<filename>/etc/shorewall/interfaces</filename>.</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Enabling other Connections</title>
|
|
|
|
<para>If you wish to enable connections from the internet to your
|
|
firewall, the general format of a rule in <filename>/etc/shorewall/rules</filename>
|
|
is:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
|
|
ACCEPT net fw <emphasis><protocol></emphasis> <emphasis><port></emphasis></programlisting>
|
|
|
|
<example>
|
|
<title>You want to run a Web Server and a POP3 Server on your firewall
|
|
system:</title>
|
|
|
|
<para><programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
|
|
ACCEPT net fw tcp 80
|
|
ACCEPT net fw tcp 110</programlisting></para>
|
|
</example>
|
|
|
|
<para>If you don't know what port and protocol a particular
|
|
application uses, see <ulink url="ports.htm">here</ulink>.</para>
|
|
|
|
<important>
|
|
<para>I don't recommend enabling telnet to/from the internet because
|
|
it uses clear text (even for login!). If you want shell access to your
|
|
firewall from the internet, use SSH:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
|
|
ACCEPT net fw tcp 22</programlisting>
|
|
</important>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>At this point, edit /etc/shorewall/rules to add other connections as
|
|
desired.</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Starting and Stopping Your Firewall</title>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
|
|
|
|
<para>The <ulink url="Install.htm">installation procedure</ulink>
|
|
configures your system to start Shorewall at system boot but beginning
|
|
with Shorewall version 1.3.9 startup is disabled so that your system
|
|
won't try to start Shorewall before configuration is complete. Once
|
|
you have completed configuration of your firewall, you can enable
|
|
Shorewall startup by removing the file <filename>/etc/shorewall/startup_disabled</filename>.</para>
|
|
|
|
<important>
|
|
<para><emphasis role="bold">Users of the .deb package must edit
|
|
<filename>/etc/default/shorewall</filename> and set <quote>startup=1</quote>.</emphasis></para>
|
|
</important>
|
|
|
|
<para>The firewall is started using the <quote><command>shorewall start</command></quote>
|
|
command and stopped using <quote><command>shorewall stop</command></quote>.
|
|
When the firewall is stopped, routing is enabled on those hosts that have
|
|
an entry in <filename><ulink url="Documentation.htm#Routestopped">/etc/shorewall/routestopped</ulink></filename>.
|
|
A running firewall may be restarted using the <quote><command>shorewall
|
|
restart</command></quote> command. If you want to totally remove any trace
|
|
of Shorewall from your Netfilter configuration, use <quote><command>shorewall
|
|
clear</command></quote>.</para>
|
|
|
|
<warning>
|
|
<para>If you are connected to your firewall from the internet, do not
|
|
issue a <quote><command>shorewall stop</command></quote> command unless
|
|
you have added an entry for the IP address that you are connected from
|
|
to <ulink url="Documentation.htm#Routestopped"><filename>/etc/shorewall/routestopped</filename></ulink>.
|
|
Also, I don't recommend using <quote><command>shorewall restart</command></quote>;
|
|
it is better to create an <emphasis><ulink
|
|
url="configuration_file_basics.htm#Configs">alternate configuration</ulink></emphasis>
|
|
and test it using the <ulink url="starting_and_stopping_shorewall.htm"><quote><command>shorewall
|
|
try</command></quote> command</ulink>.</para>
|
|
</warning>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Additional Recommended Reading</title>
|
|
|
|
<para>I highly recommend that you review the <ulink
|
|
url="configuration_file_basics.htm">Common Configuration File Features
|
|
page</ulink> -- it contains helpful tips about Shorewall features than
|
|
make administering your firewall easier.</para>
|
|
</section>
|
|
|
|
<appendix>
|
|
<title>Revision History</title>
|
|
|
|
<para><revhistory><revision><revnumber>1.5</revnumber><date>2003-01-05</date><authorinitials>TE</authorinitials><revremark>Standards
|
|
Changes</revremark></revision><revision><revnumber>1.4</revnumber><date>2003-12-30</date><authorinitials>TE</authorinitials><revremark>Add
|
|
tip about /etc/shorewall/rfc1918 updates.</revremark></revision><revision><revnumber>1.3</revnumber><date>2003-11-15</date><authorinitials>TE</authorinitials><revremark>Initial
|
|
Docbook Conversion</revremark></revision></revhistory></para>
|
|
</appendix>
|
|
</article> |