2002-08-13 22:45:21 +02:00
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<title>Shorewall Extension Scripts</title>
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2002-08-22 23:21:41 +02:00
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<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" width="100%" id="AutoNumber1" bgcolor="#400169" height="90">
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<td width="100%">
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<h1 align="center"><font color="#FFFFFF">Extension Scripts</font></h1>
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</td>
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</tr>
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</table>
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2002-08-13 22:45:21 +02:00
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<p>
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Extension scripts are user-provided
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scripts that are invoked at various points during firewall start, restart,
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stop and clear. The scripts are placed in /etc/shorewall and are processed
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using the Bourne shell "source" mechanism. The following scripts can be
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supplied:</p>
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<ul>
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<li>init -- invoked early in "shorewall start" and "shorewall restart"</li>
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<li>start -- invoked after the firewall has been started or restarted.</li>
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<li>stop -- invoked as a first step when the firewall is being stopped.</li>
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<li>stopped -- invoked after the firewall has been stopped.</li>
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<li>clear -- invoked after the firewall has been cleared.</li>
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<li>refresh -- invoked while the firewall is being refreshed but before the
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common and/or blacklst chains have been rebuilt.</li>
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<li>newnotsyn (added in version 1.3.6) -- invoked after the 'newnotsyn' chain
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has been created but before any rules have been added to it.</li>
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</ul>
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<p>
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You can also supply a script with the same name as any of the filter
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chains in the firewall and the script will be invoked after the /etc/shorewall/rules
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file has been processed but before the /etc/shorewall/policy file has
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been processed.</p>
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2002-08-22 23:21:41 +02:00
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<p>The /etc/shorewall/common file receives special treatment. If this file is present, the rules that it
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defines will totally replace the default rules in the common chain. These
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default rules are contained in the file /etc/shorewall/common.def which
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2002-08-22 23:21:41 +02:00
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may be used as a starting point for making your own customized file.</p>
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2002-08-13 22:45:21 +02:00
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<p>
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Rather than running iptables directly, you should run it using the function
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run_iptables. Similarly, rather than running "ip" directly, you should
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use run_ip. These functions accept the same arguments as the underlying
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command but cause the firewall to be stopped if an error occurs during
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processing of the command.</p>
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<p>
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2002-08-22 23:21:41 +02:00
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If you decide to create /etc/shorewall/common it is a good idea to use the
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following technique</p>
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2002-08-13 22:45:21 +02:00
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<p>
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/etc/shorewall/common:</p>
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<blockquote>
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<pre>. /etc/shorewall/common.def
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<add your rules here></pre>
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</blockquote>
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<p>If you need to supercede a rule in the released common.def file, you can add
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the superceding rule before the '.' command. Using this technique allows
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you to add new rules while still getting the benefit of the latest common.def
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file.</p>
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2002-08-22 23:21:41 +02:00
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<p>Remember that /etc/shorewall/common defines rules
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that are only applied if the applicable policy is DROP or REJECT. These rules
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are NOT applied if the policy is ACCEPT or CONTINUE.</p>
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<p>If you set ALLOWRELATED=No in shorewall.conf, then most ICMP packets will be
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rejected by the firewall. It is recommended with this setting that you create
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the file /etc/shorewall/icmpdef and in it place the following commands:</p>
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2002-08-13 22:45:21 +02:00
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2002-08-22 23:21:41 +02:00
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<pre> run_iptables -A icmpdef -p ICMP --icmp-type echo-reply -j ACCEPT
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run_iptables -A icmpdef -p ICMP --icmp-type source-quench -j ACCEPT
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run_iptables -A icmpdef -p ICMP --icmp-type destination-unreachable -j ACCEPT
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run_iptables -A icmpdef -p ICMP --icmp-type time-exceeded -j ACCEPT
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run_iptables -A icmpdef -p ICMP --icmp-type parameter-problem -j ACCEPT
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</pre>
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<p align="left"><font size="2">Last updated
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8/22/2002 - <a href="support.htm">Tom
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2002-08-13 22:45:21 +02:00
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Eastep</a></font></p>
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<p align="left"><a href="copyright.htm"><font size="2">Copyright 2002 Thomas M. Eastep</font></a></p>
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