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shorewall_code/STABLE/documentation/standalone.htm
teastep dbfc838988 Shorewall 1.4.8 
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@789 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
2003-11-17 21:06:32 +00:00

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<meta http-equiv="Content-Language" content="en-us">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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<title>Standalone Firewall</title>
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<body>
<h1 style="text-align: center;">Standalone Firewall<br>
</h1>
<p align="left">Setting up Shorewall on a standalone Linux system is
very easy if you understand the basics and follow the documentation.</p>
<p>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:</p>
<ul>
<li>Linux system</li>
<li>Single external IP address</li>
<li>Connection through Cable Modem, DSL, ISDN, Frame Relay,
dial-up...</li>
</ul>
<p>Shorewall requires that you have the iproute/iproute2 package
installed (on RedHat, the package is called <i>iproute</i>)<i>. </i>You
can tell if this package is installed by the presence of an <b>ip</b>
program
on your firewall system. As root, you can use the 'which' command to
check for this program:</p>
<pre> [root@gateway root]# which ip<br> /sbin/ip<br> [root@gateway root]#</pre>
<p>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.&nbsp; Points at which configuration changes are
recommended are
flagged with <img border="0" src="images/BD21298_.gif" width="13"
height="13"> .</p>
<p><img border="0" src="images/j0213519.gif" width="60" height="60">
&nbsp;&nbsp;&nbsp; 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.</p>
<ul>
<li><a href="http://www.simtel.net/pub/pd/51438.html">Windows Version
of dos2unix</a></li>
<li><a href="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux
Version of dos2unix</a></li>
</ul>
<h2 align="left">PPTP/ADSL</h2>
<img style="border: 0px solid ; width: 13px; height: 13px;"
src="images/BD21298_3.gif" title="" alt="">&nbsp;&nbsp;&nbsp; If you
have an ADSL Modem and you use PPTP to communicate with a server in
that modem, you must make the <a href="PPTP.htm#PPTP_ADSL">changes
recommended here</a> in addition to those described in the steps below.
ADSL with PPTP is most commonly found in Europe, notably in Austria.<br>
<h2 align="left">Shorewall Concepts</h2>
<p> <img border="0" src="images/BD21298_.gif" width="13" height="13"
alt=""> &nbsp;&nbsp;&nbsp; The configuration files for Shorewall are
contained in the directory /etc/shorewall -- for simple setups, you
only need to deal with a few of these as described in this guide. After
you have <a href="Install.htm">installed Shorewall</a>, <b>download
the <a href="http://www1.shorewall.net/pub/shorewall/Samples/">one-interface
sample</a>, 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)</b>.</p>
<p>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.</p>
<p>Shorewall views the network where it is running as being composed of
a set of <i>zones.</i> In the one-interface sample configuration, only
one zone is defined:</p>
<table border="0" style="border-collapse: collapse;" cellpadding="3"
cellspacing="0" id="AutoNumber2">
<tbody>
<tr>
<td><u><b>Name</b></u></td>
<td><u><b>Description</b></u></td>
</tr>
<tr>
<td><b>net</b></td>
<td><b>The Internet</b></td>
</tr>
</tbody>
</table>
<p>Shorewall zones are defined in <a href="Documentation.htm#Zones">
/etc/shorewall/zones</a>.</p>
<p>Shorewall also recognizes the firewall system as its own zone - by
default, the firewall itself is known as <b>fw</b>.</p>
<p>Rules about what traffic to allow and what traffic to deny are
expressed in terms of zones.</p>
<ul>
<li>You express your default policy for connections from one zone to
another zone in the<a href="Documentation.htm#Policy">
/etc/shorewall/policy </a>file.</li>
<li>You define exceptions to those default policies in the <a
href="Documentation.htm#Rules">/etc/shorewall/rules </a>file.</li>
</ul>
<p>For each connection request entering the firewall, the request is
first checked against the /etc/shorewall/rules file. If no rule in that
file matches the connection request then the first policy in
/etc/shorewall/policy that matches the request is applied. If that
policy is REJECT or DROP&nbsp; the request is first checked against the
rules in /etc/shorewall/common (the samples provide that file for you).</p>
<p>The /etc/shorewall/policy file included with the one-interface
sample
has the following policies:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber3">
<tbody>
<tr>
<td><u><b>SOURCE ZONE</b></u></td>
<td><u><b>DESTINATION ZONE</b></u></td>
<td><u><b>POLICY</b></u></td>
<td><u><b>LOG LEVEL</b></u></td>
<td><u><b>LIMIT:BURST</b></u></td>
</tr>
<tr>
<td>fw</td>
<td>net</td>
<td>ACCEPT</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td>net</td>
<td>all<br>
</td>
<td>DROP</td>
<td>info</td>
<td>&nbsp;</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>REJECT</td>
<td>info</td>
<td>&nbsp;</td>
</tr>
</tbody>
</table>
</blockquote>
<p>The above policy will:</p>
<ol>
<li>allow all connection requests from the firewall to the internet</li>
<li>drop (ignore) all connection requests from the internet
to your firewall</li>
<li>reject all other connection requests (Shorewall requires this
catchall policy).</li>
</ol>
<p>At this point, edit your /etc/shorewall/policy and make any changes
that you wish.</p>
<h2 align="left">External Interface</h2>
<p align="left">The firewall has a single network interface. Where
Internet connectivity is through a cable or DSL "Modem", the <i>External
Interface</i> will be the ethernet adapter (<b>eth0</b>) that is
connected to that "Modem"&nbsp; <u>unless</u> you connect via <i><u>P</u>oint-to-<u>P</u>oint
<u>P</u>rotocol over <u>E</u>thernet</i> (PPPoE) or <i><u>P</u>oint-to-<u>P</u>oint
<u>T</u>unneling <u>P</u>rotocol </i>(PPTP) in which case the
External Interface will be a <b>ppp0</b>. If you connect via a regular
modem, your External Interface will also be <b>ppp0</b>. If you
connect using ISDN, your external interface will be<b> ippp0.</b></p>
<p align="left"><img border="0" src="images/BD21298_3.gif" width="13"
height="13"> &nbsp;&nbsp;&nbsp; The Shorewall one-interface sample
configuration assumes that the external interface is <b>eth0</b>. 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:</p>
<ul>
<li>
<p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>,
you can replace the "detect" in the second column with "-". </p>
</li>
<li>
<p align="left">If your external interface is <b>ppp0</b> or <b>ippp0</b>
or if you have a static IP address, you can remove "dhcp" from the
option list.<br>
</p>
</li>
</ul>
<div align="left">
<h2 align="left">IP Addresses</h2>
</div>
<div align="left">
<p align="left">RFC 1918 reserves several <i>Private </i>IP address
ranges for use in private networks:</p>
<div align="left">
<pre> 10.0.0.0 - 10.255.255.255<br> 172.16.0.0 - 172.31.255.255<br> 192.168.0.0 - 192.168.255.255</pre>
</div>
<p align="left">These addresses are sometimes referred to as <i>non-routable</i>
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 <i>Network Address
Translation </i>to rewrite packet headers when forwarding to/from the
internet.</p>
<p align="left"><img border="0" src="images/BD21298_.gif" align="left"
width="13" height="13"> &nbsp;&nbsp;&nbsp;&nbsp; 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 'norfc1918'
option from the entry in /etc/shorewall/interfaces.</p>
</div>
<div align="left">
<h2 align="left">Enabling other Connections</h2>
</div>
<div align="left">
<p align="left">If you wish to enable connections from the internet to
your firewall, the general format is:</p>
</div>
<div align="left">
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber4">
<tbody>
<tr>
<td><u><b>ACTION</b></u></td>
<td><u><b>SOURCE</b></u></td>
<td><u><b>DESTINATION</b></u></td>
<td><u><b>PROTOCOL</b></u></td>
<td><u><b>PORT</b></u></td>
<td><u><b>SOURCE PORT</b></u></td>
<td><u><b>ORIGINAL ADDRESS</b></u></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>net</td>
<td>fw</td>
<td><i>&lt;protocol&gt;</i></td>
<td><i>&lt;port&gt;</i></td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">Example - You want to run a Web Server and a POP3
Server
on your firewall system:</p>
</div>
<div align="left">
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber5">
<tbody>
<tr>
<td><u><b>ACTION</b></u></td>
<td><u><b>SOURCE</b></u></td>
<td><u><b>DESTINATION</b></u></td>
<td><u><b>PROTOCOL</b></u></td>
<td><u><b>PORT</b></u></td>
<td><u><b>SOURCE PORT</b></u></td>
<td><u><b>ORIGINAL ADDRESS</b></u></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>net</td>
<td>fw</td>
<td>tcp</td>
<td>80</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<td>ACCEPT</td>
<td>net</td>
<td>fw</td>
<td>tcp</td>
<td>110</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">If you don't know what port and protocol a particular
application uses, see <a href="ports.htm">here</a>.</p>
</div>
<div align="left">
<p align="left"><b>Important: </b>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:</p>
</div>
<div align="left">
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber4">
<tbody>
<tr>
<td><u><b>ACTION</b></u></td>
<td><u><b>SOURCE</b></u></td>
<td><u><b>DESTINATION</b></u></td>
<td><u><b>PROTOCOL</b></u></td>
<td><u><b>PORT</b></u></td>
<td><u><b>SOURCE PORT</b></u></td>
<td><u><b>ORIGINAL ADDRESS</b></u></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>net</td>
<td>fw</td>
<td>tcp</td>
<td>22</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_3.gif" width="13"
height="13"> &nbsp;&nbsp;&nbsp; At this point, edit
/etc/shorewall/rules to add other connections as desired.</p>
</div>
<div align="left">
<h2 align="left">Starting and Stopping Your Firewall</h2>
</div>
<div align="left">
<p align="left"> <img border="0" src="images/BD21298_2.gif" width="13"
height="13" alt="Arrow"> &nbsp;&nbsp;&nbsp; The <a href="Install.htm">installation
procedure </a> 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
/etc/shorewall/startup_disabled.<br>
</p>
<p align="left"><font color="#ff0000"><b>IMPORTANT</b>: Users of the
.deb package must edit /etc/default/shorewall and set 'startup=1'.</font><br>
</p>
</div>
<div align="left">
<p align="left">The firewall is started using the "shorewall start"
command and stopped using "shorewall stop". When the firewall is
stopped,
routing is enabled on those hosts that have an entry in <a
href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
A running firewall may be restarted using the "shorewall restart"
command. If you want to totally remove any trace of Shorewall from your
Netfilter configuration, use "shorewall clear".</p>
</div>
<div align="left">
<p align="left"><b>WARNING: </b>If you are connected to your firewall
from the internet, do not issue a "shorewall stop" command unless you
have added an entry for the IP address that you are connected from
to <a href="Documentation.htm#Routestopped">/etc/shorewall/routestopped</a>.
Also, I don't recommend using "shorewall restart"; it is better to
create an <i><a href="configuration_file_basics.htm#Configs">alternate
configuration</a></i> and test it using the <a
href="starting_and_stopping_shorewall.htm">"shorewall try" command</a>.<br>
</p>
<h2>Additional Recommended Reading</h2>
I highly recommend that you review the <a
href="configuration_file_basics.htm">Common Configuration File
Features page</a> -- it contains helpful tips about Shorewall features
than make administering your firewall easier.<br>
</div>
<p align="left"><font size="2">Last updated 10/29/2003 - <a
href="support.htm">Tom Eastep</a></font></p>
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002,
2003 Thomas M. Eastep</font></a></p>
</body>
</html>
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