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<title>Two-Interface Firewall</title>
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<h1 align="center"><font color="#ffffff">Basic Two-Interface Firewall</font></h1>
</td>
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</table>
<p align="left">Setting up a Linux system as a firewall for a small network
is a fairly straight-forward task 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 its most common configuration:</p>
<ul>
<li>Linux system used as a firewall/router for a small
local network.</li>
<li>Single public IP address.</li>
<li>Internet connection through cable modem, DSL, ISDN,
Frame Relay, dial-up ...</li>
</ul>
<p align="left">Here is a schematic of a typical installation.</p>
<p align="center"> <img border="0" src="images/basics.png" width="444"
height="635">
</p>
<p><b>If you are running Shorewall under Mandrake 9.0 or later, you can easily
configure the above setup using the Mandrake "Internet Connection Sharing"
applet. From the Mandrake Control Center, select "Network &amp; Internet"
then "Connection Sharing".<br>
</b></p>
<p><b>Note however, that the Shorewall configuration produced by Mandrake
Internet Connection Sharing is strange and is apt to confuse you if you
use the rest of this documentation (it has two local zones; "loc" and "masq"
where "loc" is empty; this conflicts with this documentation which assumes
a single local zone "loc"). We therefore recommend that once you have set
up this sharing that you uninstall the Mandrake Shorewall RPM and install
the one from the <a href="download.htm">download page</a> then follow the
instructions in this Guide.</b><br>
</p>
<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 first read through the guide to familiarize yourself
with what's involved then go back through it again making your
configuration changes. Points at which configuration changes are
recommended are flagged with <img border="0"
src="images/BD21298_.gif" width="13" height="13">
. Configuration notes that are unique to LEAF/Bering are
marked with<74><img src="images/leaflogo.gif" alt="(LEAF Logo)"
width="49" height="36">
</p>
<p><img border="0" src="images/j0213519.gif" width="60" height="60">
<20><><EFBFBD> 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">Shorewall Concepts</h2>
<p> <img border="0" src="images/BD21298_.gif" width="13" height="13"
alt="">
<20><><EFBFBD> The configuration files for Shorewall are contained in the
directory /etc/shorewall -- for simple setups, you will 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/">two-interface sample</a>,
un-tar it (tar -zxvf two-interfaces.tgz) and and copy the files to
/etc/shorewall (these files will replace files with the same name).</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 two-interface sample configuration,
the following zone names are used:</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>
<tr>
<td><b>loc</b></td>
<td><b>Your Local Network</b></td>
</tr>
</tbody>
</table>
<p>Zones are defined in the <a href="Documentation.htm#Zones"> /etc/shorewall/zones</a>
file.</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<4F> 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 two-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>loc</td>
<td>net</td>
<td>ACCEPT</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
<td><EFBFBD></td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>REJECT</td>
<td>info</td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<blockquote>
<p>In the two-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.</p>
<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><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<p>The above policy will:</p>
<ol>
<li>allow all connection requests from your local network
to the internet</li>
<li>drop (ignore) all connection requests from the internet
to your firewall or local network</li>
<li>optionally accept all connection requests from the
firewall to the internet (if you uncomment the additional policy)</li>
<li>reject all other connection requests.</li>
</ol>
<p><img border="0" src="images/BD21298_.gif" width="13" height="13">
<20><><EFBFBD> At this point, edit your /etc/shorewall/policy and
make any changes that you wish.</p>
<h2 align="left">Network Interfaces</h2>
<p align="center"> <img border="0" src="images/basics.png" width="444"
height="635">
</p>
<p align="left">The firewall has two network interfaces. Where Internet connectivity
is through a cable or DSL "Modem", the <i>External Interface</i> will be
the ethernet adapter that is connected to that "Modem" (e.g., <b>eth0</b>)<29>
<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 ppp interface (e.g., <b>ppp0</b>). If you connect
via a regular modem, your External Interface will also be <b>ppp0</b>.
If you connect via ISDN, your external interface will be <b>ippp0.</b></p>
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
height="13">
<20><><EFBFBD> If your external interface is <b>ppp0</b> or<b> ippp0</b><EFBFBD>
then you will want to set CLAMPMSS=yes in <a
href="Documentation.htm#Conf"> /etc/shorewall/shorewall.conf.</a></p>
<p align="left">Your <i>Internal Interface</i> will be an ethernet adapter
(eth1 or eth0) and will be connected to a hub or switch. Your other
computers will be connected to the same hub/switch (note: If you
have only a single internal system, you can connect the firewall
directly to the computer using a <i>cross-over </i> cable).</p>
<p align="left"><u><b> <img border="0" src="images/j0213519.gif"
width="60" height="60">
</b></u>Do not connect the internal and external interface
to the same hub or switch (even for testing). It won't work the way
that you think that it will and you will end up confused and believing
that Shorewall doesn't work at all.</p>
<p align="left"><img border="0" src="images/BD21298_.gif" align="left"
width="13" height="13">
<20><><EFBFBD> The Shorewall two-interface sample configuration assumes
that the external interface is <b>eth0</b> and the internal interface
is <b>eth1</b>. If your configuration is different, you will have
to modify the sample <a href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a>
file accordingly. While you are there, you may wish to review the
list of options that are specified for the interfaces. 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. </p>
</li>
</ul>
<h2 align="left">IP Addresses</h2>
<p align="left">Before going further, we should say a few words about Internet
Protocol (IP) <i>addresses</i>. Normally, your ISP will assign
you a single <i> Public</i> IP address. This address may be assigned
via the<i> Dynamic Host Configuration Protocol</i> (DHCP) or as part
of establishing your connection when you dial in (standard modem) or
establish your PPP connection. In rare cases, your ISP may assign you
a<i> static</i> IP address; that means that you configure your firewall's
external interface to use that address permanently.<i> </i>However
your external address is assigned, it will be shared by all of your systems
when you access the Internet. You will have to assign your own addresses
in your internal network (the Internal Interface on your firewall plus
your other computers). RFC 1918 reserves several <i>Private </i>IP address
ranges for this purpose:</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>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
height="13">
<20><><EFBFBD> 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
external interface's entry in /etc/shorewall/interfaces.</p>
</div>
<div align="left">
<p align="left">You will want to assign your addresses from the same <i>
sub-network </i>(<i>subnet)</i>.<2E> For our purposes, we can consider a subnet
to consists of a range of addresses x.y.z.0 - x.y.z.255. Such
a subnet will have a <i>Subnet Mask </i>of 255.255.255.0. The address
x.y.z.0 is reserved as the <i>Subnet Address</i> and x.y.z.255
is reserved as the <i>Subnet Broadcast</i> <i>Address</i>. In Shorewall,
a subnet is described using<6E><a
href="shorewall_setup_guide.htm#Subnets"><i>Classless InterDomain Routing
</i>(CIDR) notation</a> with consists of the subnet address followed
by "/24". The "24" refers to the number of consecutive leading "1"
bits from the left of the subnet mask. </p>
</div>
<div align="left">
<p align="left">Example sub-network:</p>
</div>
<div align="left">
<blockquote>
<table border="1" style="border-collapse: collapse;" id="AutoNumber1"
cellpadding="2">
<tbody>
<tr>
<td><b>Range:</b></td>
<td>10.10.10.0 - 10.10.10.255</td>
</tr>
<tr>
<td><b>Subnet Address:</b></td>
<td>10.10.10.0</td>
</tr>
<tr>
<td><b>Broadcast Address:</b></td>
<td>10.10.10.255</td>
</tr>
<tr>
<td><b>CIDR<EFBFBD>Notation:</b></td>
<td>10.10.10.0/24</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">It is conventional to assign the internal interface either
the first usable address in the subnet (10.10.10.1 in the above
example) or the last usable address (10.10.10.254).</p>
</div>
<div align="left">
<p align="left">One of the purposes of subnetting is to allow all computers
in the subnet to understand which other computers can be communicated
with directly. To communicate with systems outside of the subnetwork,
systems send packets through a<i><EFBFBD> gateway</i><EFBFBD> (router).</p>
</div>
<div align="left">
<p align="left"><img border="0" src="images/BD21298_1.gif" width="13"
height="13">
<20><><EFBFBD> Your local computers (computer 1 and computer 2
in the above diagram) should be configured with their<i> default
gateway</i> to be the IP address of the firewall's internal interface.<i><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
</i> </p>
</div>
<p align="left">The foregoing short discussion barely scratches the surface
regarding subnetting and routing. If you are interested in learning
more about IP addressing and routing, I highly recommend <i>"IP
Fundamentals: What Everyone Needs to Know about Addressing &amp;
Routing",</i> Thomas A. Maufer, Prentice-Hall, 1999, ISBN 0-13-975483-0.</p>
<p align="left">The remainder of this quide will assume that you have configured
your network as shown here:</p>
<p align="center"> <img border="0" src="images/basics1.png" width="444"
height="635">
</p>
<p align="left">The default gateway for computer's 1 &amp; 2 would be 10.10.10.254.<br>
</p>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
height="13" alt="">
<20><><EFBFBD> <font color="#ff0000"><b>WARNING: </b></font><b>Your ISP might
assign your external interface an RFC 1918 address. If that address is
in the 10.10.10.0/24 subnet then you will need to select a DIFFERENT RFC
1918 subnet for your local network.</b><br>
</p>
<h2 align="left">IP Masquerading (SNAT)</h2>
<p align="left">The addresses reserved by RFC 1918 are sometimes referred
to as <i>non-routable</i> because the Internet backbone routers
don't forward packets which have an RFC-1918 destination address.
When one of your local systems (let's assume computer 1) sends a connection
request to an internet host, the firewall must perform <i>Network
Address Translation </i>(NAT). The firewall rewrites the source address
in the packet to be the address of the firewall's external interface;
in other words, the firewall makes it look as if the firewall itself
is initiating the connection.<2E> This is necessary so that the destination
host will be able to route return packets back to the firewall (remember
that packets whose destination address is reserved by RFC 1918 can't
be routed across the internet so the remote host can't address its response
to computer 1). When the firewall receives a return packet, it rewrites
the destination address back to 10.10.10.1 and forwards the packet on
to computer 1. </p>
<p align="left">On Linux systems, the above process is often referred to
as<i> IP Masquerading</i> but you will also see the term <i>Source Network
Address Translation </i>(SNAT) used. Shorewall follows the convention used
with Netfilter:</p>
<ul>
<li>
<p align="left"><i>Masquerade</i> describes the case where you let your
firewall system automatically detect the external interface address.
</p>
</li>
<li>
<p align="left"><i>SNAT</i> refers to the case when you explicitly specify
the source address that you want outbound packets from your local
network to use. </p>
</li>
</ul>
<p align="left">In Shorewall, both Masquerading and SNAT are configured with
entries in the /etc/shorewall/masq file. You will normally use
Masquerading if your external IP is dynamic and SNAT if the IP
is static.</p>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
height="13">
<20><><EFBFBD> If your external firewall interface is <b>eth0</b>,
you do not need to modify the file provided with the sample. Otherwise,
edit /etc/shorewall/masq and change the first column to the name
of your external interface and the second column to the name of your
internal interface.</p>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
height="13">
<20><><EFBFBD> If your external IP is static, you can enter it in
the third column in the /etc/shorewall/masq entry if you like although
your firewall will work fine if you leave that column empty. Entering
your static IP in column 3 makes processing outgoing packets a little
more efficient.<br>
<br>
<img border="0" src="images/BD21298_.gif" width="13"
height="13" alt="">
<20><><EFBFBD> If you are using the Debian package, please check your shorewall.conf
file to ensure that the following are set correctly; if they are not,
change them appropriately:<br>
</p>
<ul>
<li>NAT_ENABLED=Yes</li>
<li>IP_FORWARDING=On<br>
</li>
</ul>
<h2 align="left">Port Forwarding (DNAT)</h2>
<p align="left">One of your goals may be to run one or more servers on your
local computers. Because these computers have RFC-1918 addresses,
it is not possible for clients on the internet to connect directly
to them. It is rather necessary for those clients to address their
connection requests to the firewall who rewrites the destination address
to the address of your server and forwards the packet to that server.
When your server responds, the firewall automatically performs SNAT
to rewrite the source address in the response.</p>
<p align="left">The above process is called<i> Port Forwarding</i> or <i>
Destination Network Address Translation</i> (DNAT). You configure
port forwarding using DNAT rules in the /etc/shorewall/rules file.</p>
<p>The general form of a simple port forwarding rule in /etc/shorewall/rules
is:</p>
<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>DNAT</td>
<td>net</td>
<td>loc:<i>&lt;server local ip address&gt; </i>[:<i>&lt;server
port&gt;</i>]</td>
<td><i>&lt;protocol&gt;</i></td>
<td><i>&lt;port&gt;</i></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<p>Example - you run a Web Server on computer 2 and you want to forward incoming
TCP port 80 to that system:</p>
<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>DNAT</td>
<td>net</td>
<td>loc:10.10.10.2</td>
<td>tcp</td>
<td>80</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<p>A couple of important points to keep in mind:</p>
<ul>
<li>You must test the above rule from a client outside
of your local network (i.e., don't test from a browser running
on computers 1 or 2 or on the firewall). If you want to be able
to access your web server using the IP address of your external interface,
see <a href="FAQ.htm#faq2">Shorewall FAQ #2</a>.</li>
<li>Many ISPs block incoming connection requests to
port 80. If you have problems connecting to your web server, try
the following rule and try connecting to port 5000.</li>
</ul>
<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>DNAT</td>
<td>net</td>
<td>loc:10.10.10.2:80</td>
<td>tcp</td>
<td>5000</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<p> <img border="0" src="images/BD21298_.gif" width="13" height="13">
<20><><EFBFBD> At this point, modify /etc/shorewall/rules to add
any DNAT rules that you require.</p>
<h2 align="left">Domain Name Server (DNS)</h2>
<p align="left">Normally, when you connect to your ISP, as part of getting
an IP address your firewall's <i>Domain Name Service </i>(DNS)
resolver will be automatically configured (e.g., the /etc/resolv.conf
file will be written). Alternatively, your ISP may have given you
the IP address of a pair of DNS <i> name servers</i> for you to manually
configure as your primary and secondary name servers. Regardless of
how DNS gets configured on your firewall, it is <u>your</u> responsibility
to configure the resolver in your internal systems. You can take one
of two approaches:</p>
<ul>
<li>
<p align="left">You can configure your internal systems to use your ISP's
name servers. If you ISP gave you the addresses of their servers
or if those addresses are available on their web site, you can
configure your internal systems to use those addresses. If that
information isn't available, look in /etc/resolv.conf on your firewall
system -- the name servers are given in "nameserver" records in that
file. </p>
</li>
<li>
<p align="left"><img border="0" src="images/BD21298_.gif" width="13"
height="13">
<20><><EFBFBD> You can configure a<i> Caching Name Server </i>on your
firewall.<i> </i>Red Hat has an RPM for a caching name server
(the RPM also requires the 'bind' RPM) and for Bering users, there
is dnscache.lrp. If you take this approach, you configure your internal
systems to use the firewall itself as their primary (and only) name
server. You use the internal IP address of the firewall (10.10.10.254
in the example above) for the name server address. To allow your local
systems to talk to your caching name server, you must open port 53
(both UDP and TCP) from the local network to the firewall; you do
that by adding the following rules in /etc/shorewall/rules. </p>
</li>
</ul>
<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>loc</td>
<td>fw</td>
<td>tcp</td>
<td>53</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc</td>
<td>fw</td>
<td>udp</td>
<td>53</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<div align="left">
<h2 align="left">Other Connections</h2>
</div>
<div align="left">
<p align="left">The two-interface sample includes the following rules:</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>fw</td>
<td>net</td>
<td>tcp</td>
<td>53</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>fw</td>
<td>net</td>
<td>udp</td>
<td>53</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">Those rules allow DNS access from your firewall and may be
removed if you uncommented the line in /etc/shorewall/policy
allowing all connections from the firewall to the internet.</p>
</div>
<div align="left">
<p align="left">The sample also includes:</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>loc</td>
<td>fw</td>
<td>tcp</td>
<td>22</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">That rule allows you to run an SSH server on your firewall
and connect to that server from your local systems.</p>
</div>
<div align="left">
<p align="left">If you wish to enable other connections between your firewall
and other systems, 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><i>&lt;source zone&gt;</i></td>
<td><i>&lt;destination zone&gt;</i></td>
<td><i>&lt;protocol&gt;</i></td>
<td><i>&lt;port&gt;</i></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">Example - You want to run a Web Server on your firewall system:</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>80</td>
<td>#Allow web access</td>
<td>from the internet</td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc</td>
<td>fw</td>
<td>tcp</td>
<td>80</td>
<td>#Allow web access</td>
<td>from the local network</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left">Those two rules would of course be in addition to the rules
listed above under "You can configure a Caching Name Server on
your firewall"</p>
</div>
<div align="left">
<p align="left">If you don't know what port and protocol a particular application
uses, look <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><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div align="left">
<p align="left"><img src="images/leaflogo.gif" alt="(LEAF Logo)"
width="49" height="36">
<20><><EFBFBD> Bering users will want to add the following two rules to be compatible
with Jacques's Shorewall configuration.</p>
<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>loc<br>
</td>
<td>fw</td>
<td>udp<br>
</td>
<td>53<br>
</td>
<td>#Allow DNS Cache to</td>
<td>work<br>
</td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc</td>
<td>fw</td>
<td>tcp</td>
<td>80</td>
<td>#Allow weblet to work</td>
<td><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<p align="left"><br>
<img border="0" src="images/BD21298_.gif" width="13" height="13">
<20><><EFBFBD> Now edit your /etc/shorewall/rules file to add or
delete other connections as required.</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">
<20><><EFBFBD> The <a href="Install.htm">installation procedure </a>
configures your system to start Shorewall at system boot<6F> 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>: </font><font
color="#ff0000">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"><img border="0" src="images/BD21298_.gif" width="13"
height="13">
<20><><EFBFBD> The two-interface sample assumes that you want to enable
routing to/from <b>eth1 </b>(the local network) when Shorewall
is stopped. If your local network isn't connected to <b>eth1</b> or
if you wish to enable access to/from other hosts, change /etc/shorewall/routestopped
accordingly.</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>.</p>
</div>
<p align="left"><font size="2">Last updated 2/21/2003 - <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><br>
</p>
<br>
<br>
<br>
<br>
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