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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><a name="Files"></a>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>
<li>/etc/shorewall/init - commands that you wish to execute at the beginning
of a "shorewall start" or "shorewall restart".</li>
<li>/etc/shorewall/start - commands that you wish to execute at the
completion of a "shorewall start" or "shorewall restart"</li>
<li>/etc/shorewall/stop - commands that you wish to execute at the beginning
of a "shorewall stop".</li>
<li>/etc/shorewall/stopped - commands that you wish to execute at the
completion of a "shorewall stop".<br>
</li>
</ul>
<h2><a name="Comments"></a>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><a name="Continuation"></a>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 as either IP addresses or 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 changes 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. (note the trailing period).</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 restrictions are not imposed by Shorewall simply for
your inconvenience but are rather limitations of iptables.<br>
<h2><a name="Compliment"></a>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". There must be
no white space following the "!".</p>
<h2><a name="Lists"></a>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><a name="Ports"></a>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><a name="Ranges"></a>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>>. For example,
if you want to forward the range of tcp ports 4000 through 4100 to local
host 192.168.1.3, the entry in /etc/shorewall/rules is:<br>
</p>
<pre> DNAT net loc:192.168.1.3 tcp 4000:4100<br></pre>
If you omit the low port number, a value of zero is assumed; if you omit
the high port number, a value of 65535 is assumed.<br>
<h2><a name="Variables"></a>Using Shell Variables</h2>
<p>You may use the /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><a name="MAC"></a>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".<br>
</p>
<p><b>Note: </b>It is not necessary to use the special Shorewall notation
in the <a href="MAC_Validation.html">/etc/shorewall/maclist</a> file.<br>
</p>
<h2><a name="Levels"></a>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 2/7/2003 - <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, 2003 Thomas M. Eastep.</font></a></font><br>
</p>
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