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<title>Shorewall Extension Scripts</title>
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<h1 align="center"><font color="#ffffff">Extension Scripts</font></h1>
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<p> Extension scripts are user-provided scripts that are invoked at various
points during firewall start, restart, stop and clear. The scripts are
placed in /etc/shorewall and are processed using the Bourne shell "source"
mechanism. The following scripts can be supplied:</p>
<ul>
<li>init -- invoked early in "shorewall start" and "shorewall restart"</li>
<li>start -- invoked after the firewall has been started or restarted.</li>
<li>stop -- invoked as a first step when the firewall is being stopped.</li>
<li>stopped -- invoked after the firewall has been stopped.</li>
<li>clear -- invoked after the firewall has been cleared.</li>
<li>refresh -- invoked while the firewall is being refreshed but before
the common and/or blacklst chains have been rebuilt.</li>
<li>newnotsyn (added in version 1.3.6) -- invoked after the 'newnotsyn'
chain has been created but before any rules have been added to it.</li>
</ul>
<p><u><b>If your version of Shorewall doesn't have the file that you want
to use from the above list, you can simply create the file yourself.</b></u></p>
<p> You can also supply a script with the same name as any of the filter
chains in the firewall and the script will be invoked after the /etc/shorewall/rules
file has been processed but before the /etc/shorewall/policy file has been
processed.</p>
<p>The /etc/shorewall/common file receives special treatment. If this file
is present, the rules that it defines will totally replace the default
rules in the common chain. These default rules are contained in the
file /etc/shorewall/common.def which may be used as a starting point
for making your own customized file.</p>
<p> Rather than running iptables directly, you should run it using the
function run_iptables. Similarly, rather than running "ip" directly,
you should use run_ip. These functions accept the same arguments as the
underlying command but cause the firewall to be stopped if an error occurs
during processing of the command.</p>
<p> If you decide to create /etc/shorewall/common it is a good idea to
use the following technique</p>
<p> /etc/shorewall/common:</p>
<blockquote>
<pre>. /etc/shorewall/common.def<br><add your rules here></pre>
</blockquote>
<p>If you need to supercede a rule in the released common.def file, you can
add the superceding rule before the '.' command. Using this technique allows
you to add new rules while still getting the benefit of the latest common.def
file.</p>
<p>Remember that /etc/shorewall/common defines rules that are only applied
if the applicable policy is DROP or REJECT. These rules are NOT applied
if the policy is ACCEPT or CONTINUE.</p>
<p>If you set ALLOWRELATED=No in shorewall.conf, then most ICMP packets will
be rejected by the firewall. It is recommended with this setting that you
create the file /etc/shorewall/icmpdef and in it place the following commands:</p>
<pre> run_iptables -A icmpdef -p ICMP --icmp-type echo-reply -j ACCEPT<br> run_iptables -A icmpdef -p ICMP --icmp-type source-quench -j ACCEPT<br> run_iptables -A icmpdef -p ICMP --icmp-type destination-unreachable -j ACCEPT<br> run_iptables -A icmpdef -p ICMP --icmp-type time-exceeded -j ACCEPT<br> run_iptables -A icmpdef -p ICMP --icmp-type parameter-problem -j ACCEPT<br></pre>
<p align="left"><font size="2">Last updated 12/22/2002 - <a
href="support.htm">Tom Eastep</a></font></p>
<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002 Thomas
M. Eastep</font></a></p>
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