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<h1 align="center"><font color="#ffffff">Configuration Files</font></h1>
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<p><b><font color="#ff0000">Warning: </font>If you copy or edit your
configuration files on a system running Microsoft Windows, you <u>must</u>
run them through <a
href="http://www.megaloman.com/%7Ehany/software/hd2u/"> dos2unix</a>
before you use them with Shorewall.</b></p>
<h2>Files</h2>
<p>Shorewall's configuration files are in the directory /etc/shorewall.</p>
<ul>
<li>/etc/shorewall/shorewall.conf - used to set several firewall
parameters.</li>
<li>/etc/shorewall/params - use this file to set shell variables
that you will expand in other files.</li>
<li>/etc/shorewall/zones - partition the firewall's view of the
world into <i>zones.</i></li>
<li>/etc/shorewall/policy - establishes firewall high-level policy.</li>
<li>/etc/shorewall/interfaces - describes the interfaces on the
firewall system.</li>
<li>/etc/shorewall/hosts - allows defining zones in terms of individual
hosts and subnetworks.</li>
<li>/etc/shorewall/masq - directs the firewall where to use many-to-one
(dynamic) Network Address Translation (a.k.a. Masquerading) and Source
Network Address Translation (SNAT).</li>
<li>/etc/shorewall/modules - directs the firewall to load kernel
modules.</li>
<li>/etc/shorewall/rules - defines rules that are exceptions to
the overall policies established in /etc/shorewall/policy.</li>
<li>/etc/shorewall/nat - defines static NAT rules.</li>
<li>/etc/shorewall/proxyarp - defines use of Proxy ARP.</li>
<li>/etc/shorewall/routestopped (Shorewall 1.3.4 and later) - defines
hosts accessible when Shorewall is stopped.</li>
<li>/etc/shorewall/tcrules - defines marking of packets for later
use by traffic control/shaping or policy routing.</li>
<li>/etc/shorewall/tos - defines rules for setting the TOS field
in packet headers.</li>
<li>/etc/shorewall/tunnels - defines IPSEC, GRE and IPIP tunnels
with end-points on the firewall system.</li>
<li>/etc/shorewall/blacklist - lists blacklisted IP/subnet/MAC
addresses.</li>
</ul>
<h2>Comments</h2>
<p>You may place comments in configuration files by making the first non-whitespace
character a pound sign ("#"). You may also place comments at the end
of any line, again by delimiting the comment from the rest of the line
with a pound sign.</p>
<p>Examples:</p>
<pre># This is a comment</pre>
<pre>ACCEPT net fw tcp www #This is an end-of-line comment</pre>
<h2>Line Continuation</h2>
<p>You may continue lines in the configuration files using the usual backslash
("\") followed immediately by a new line character.</p>
<p>Example:</p>
<pre>ACCEPT net fw tcp \<br>smtp,www,pop3,imap #Services running on the firewall</pre>
<h2><a name="dnsnames"></a>Using DNS Names</h2>
<p align="left"> </p>
<p align="left"><b>WARNING: I personally recommend strongly <u>against</u>
using DNS names in Shorewall configuration files. If you use DNS names and
you are called out of bed at 2:00AM because Shorewall won't start as a result
of DNS problems then don't say that you were not forewarned. <br>
</b></p>
<p align="left"><b>��� -Tom<br>
</b></p>
<p align="left">Beginning with Shorwall 1.3.9, Host addresses in Shorewall
configuration files may be specified either as IP addresses or as DNS Names.<br>
<br>
DNS names in iptables rules aren't nearly as useful as they first appear.
When a DNS name appears in a rule, the iptables utility resolves the name
to one or more IP addresses and inserts those addresses into the rule. So
change in the DNS->IP address relationship that occur after the firewall
has started have absolutely no effect on the firewall's ruleset. </p>
<p align="left"> If your firewall rules include DNS names then:</p>
<ul>
<li>If your /etc/resolv.conf is wrong then your firewall won't start.</li>
<li>If your /etc/nsswitch.conf is wrong then your firewall won't start.</li>
<li>If your Name Server(s) is(are) down then your firewall won't start.</li>
<li>If your startup scripts try to start your firewall before starting
your DNS server then your firewall won't start.<br>
</li>
<li>Factors totally outside your control (your ISP's router is down
for example), can prevent your firewall from starting.</li>
<li>You must bring up your network interfaces prior to starting your firewall.<br>
</li>
</ul>
<p align="left"> Each DNS name much be fully qualified and include a minumum
of two periods (although one may be trailing). This restriction is imposed
by Shorewall to insure backward compatibility with existing configuration
files.<br>
<br>
Examples of valid DNS names:<br>
</p>
<ul>
<li>mail.shorewall.net</li>
<li>shorewall.net.</li>
</ul>
Examples of invalid DNS names:<br>
<ul>
<li>mail (not fully qualified)</li>
<li>shorewall.net (only one period)</li>
</ul>
DNS names may not be used as:<br>
<ul>
<li>The server address in a DNAT rule (/etc/shorewall/rules file)</li>
<li>In the ADDRESS column of an entry in /etc/shorewall/masq.</li>
<li>In the /etc/shorewall/nat file.</li>
</ul>
These are iptables restrictions and are not simply imposed for your inconvenience
by Shorewall. <br>
<br>
<h2>Complementing an Address or Subnet</h2>
<p>Where specifying an IP address, a subnet or an interface, you can
precede the item with "!" to specify the complement of the item. For
example, !192.168.1.4 means "any host but 192.168.1.4".</p>
<h2>Comma-separated Lists</h2>
<p>Comma-separated lists are allowed in a number of contexts within the
configuration files. A comma separated list:</p>
<ul>
<li>Must not have any embedded white space.<br>
Valid: routestopped,dhcp,norfc1918<br>
Invalid: routestopped,���� dhcp,���� norfc1818</li>
<li>If you use line continuation to break a comma-separated list,
the continuation line(s) must begin in column 1 (or there would be
embedded white space)</li>
<li>Entries in a comma-separated list may appear in any order.</li>
</ul>
<h2>Port Numbers/Service Names</h2>
<p>Unless otherwise specified, when giving a port number you can use
either an integer or a service name from /etc/services. </p>
<h2>Port Ranges</h2>
<p>If you need to specify a range of ports, the proper syntax is <<i>low
port number</i>>:<<i>high port number</i>>.</p>
<h2>Using Shell Variables</h2>
<p>You may use the file /etc/shorewall/params file to set shell variables
that you can then use in some of the other configuration files.</p>
<p>It is suggested that variable names begin with an upper case letter<font
size="1"> </font>to distinguish them from variables used internally
within the Shorewall programs</p>
<p>Example:</p>
<blockquote>
<pre>NET_IF=eth0<br>NET_BCAST=130.252.100.255<br>NET_OPTIONS=noping,norfc1918</pre>
</blockquote>
<p><br>
Example (/etc/shorewall/interfaces record):</p>
<font
face="Century Gothic, Arial, Helvetica">
<blockquote>
<pre><font face="Courier">net $NET_IF $NET_BCAST $NET_OPTIONS</font></pre>
</blockquote>
</font>
<p>The result will be the same as if the record had been written</p>
<font
face="Century Gothic, Arial, Helvetica">
<blockquote>
<pre>net eth0 130.252.100.255 noping,norfc1918</pre>
</blockquote>
</font>
<p>Variables may be used anywhere in the other configuration
files.</p>
<h2>Using MAC Addresses</h2>
<p>Media Access Control (MAC) addresses can be used to specify packet
source in several of the configuration files. To use this feature,
your kernel must have MAC Address Match support (CONFIG_IP_NF_MATCH_MAC)
included.</p>
<p>MAC addresses are 48 bits wide and each Ethernet Controller has a
unique MAC address.<br>
<br>
In GNU/Linux, MAC addresses are usually written as a series of 6
hex numbers separated by colons. Example:<br>
<br>
���� [root@gateway root]# ifconfig eth0<br>
���� eth0 Link encap:Ethernet HWaddr <b><u>02:00:08:E3:FA:55</u></b><br>
���� inet addr:206.124.146.176 Bcast:206.124.146.255 Mask:255.255.255.0<br>
���� UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1<br>
���� RX packets:2398102 errors:0 dropped:0 overruns:0 frame:0<br>
���� TX packets:3044698 errors:0 dropped:0 overruns:0 carrier:0<br>
���� collisions:30394 txqueuelen:100<br>
���� RX bytes:419871805 (400.4 Mb) TX bytes:1659782221 (1582.8 Mb)<br>
���� Interrupt:11 Base address:0x1800<br>
<br>
Because Shorewall uses colons as a separator for address fields,
Shorewall requires MAC addresses to be written in another way. In
Shorewall, MAC addresses begin with a tilde ("~") and consist of 6
hex numbers separated by hyphens. In Shorewall, the MAC address in
the example above would be written "~02-00-08-E3-FA-55".</p>
<h2>Shorewall Configurations</h2>
<p> Shorewall allows you to have configuration directories other than /etc/shorewall.
The <a href="starting_and_stopping_shorewall.htm">shorewall start and restart</a>
commands allow you to specify an alternate configuration directory and
Shorewall will use the files in the alternate directory rather than the corresponding
files in /etc/shorewall. The alternate directory need not contain a complete
configuration; those files not in the alternate directory will be read from
/etc/shorewall.</p>
<p> This facility permits you to easily create a test or temporary configuration
by:</p>
<ol>
<li> copying the files that need modification from /etc/shorewall
to a separate directory;</li>
<li> modify those files in the separate directory; and</li>
<li> specifying the separate directory in a shorewall start or
shorewall restart command (e.g., <i><b>shorewall -c /etc/testconfig restart</b></i>
).</li>
</ol>
<p><font size="2"> Updated 9/24/2002 - <a href="support.htm">Tom Eastep</a>
</font></p>
<p><font face="Trebuchet MS"><a href="copyright.htm"><font size="2">Copyright</font>
� <font size="2">2001, 2002 Thomas M. Eastep.</font></a></font></p>
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