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151 lines
5.5 KiB
HTML
151 lines
5.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>ICMP Echo-request (Ping)</title>
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<meta http-equiv="content-type"
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content="text/html; charset=ISO-8859-1">
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<meta name="author" content="Tom Eastep">
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0"
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style="border-collapse: collapse;" bordercolor="#111111" width="100%"
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id="AutoNumber1" bgcolor="#400169" height="90">
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<tbody>
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<tr>
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<td width="100%">
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<h1 align="center"><font color="#ffffff">ICMP Echo-request (Ping)</font></h1>
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</td>
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</tr>
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</tbody>
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</table>
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<br>
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Shorewall 'Ping' management has evolved over time with the latest change
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coming in Shorewall version 1.3.14. In that version, a new option (<b>OLD_PING_HANDLING</b>)
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was added to /etc/shorewall/shorewall.conf. The value of that option determines
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the overall handling of ICMP echo requests (pings).<br>
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<h2>Shorewall Versions >= 1.3.14 with OLD_PING_HANDLING=No in /etc/shorewall/shorewall.conf</h2>
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In 1.3.14, Ping handling was put under control of the rules and policies
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just like any other connection request. In order to accept ping requests from
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zone z1 to zone z2 where the policy for z1 to z2 is not ACCEPT, you need
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a rule in /etc/shoreall/rules of the form:<br>
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<blockquote>ACCEPT <i>z1 z2
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</i>icmp 8<br>
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</blockquote>
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Example: <br>
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<br>
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To permit ping from the local zone to the firewall:<br>
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<blockquote>ACCEPT loc fw
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icmp 8<br>
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</blockquote>
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If you would like to accept 'ping' by default even when the relevant
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policy is DROP or REJECT, create <b>/etc/shorewall/icmpdef </b>if it doesn't
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already exist and in that file place the following command:<br>
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<blockquote>
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<pre><b><font color="#009900">run_iptables -A icmpdef -p icmp --icmp-type 8 -j ACCEPT<br></font></b></pre>
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</blockquote>
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With that rule in place, if you want to ignore 'ping' from z1 to z2 then
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you need a rule of the form:<br>
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<blockquote>DROP <i>z1 z2
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</i>icmp 8<br>
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</blockquote>
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Example:<br>
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<br>
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To drop ping from the internet, you would need this rule in /etc/shorewall/rules:<br>
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<blockquote>DROP net fw
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icmp 8<br>
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</blockquote>
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<blockquote> </blockquote>
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<h2>Shorewall Versions < 1.3.14 or with OLD_PING_HANDLING=Yes in /etc/shorewall/shorewall.conf<br>
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</h2>
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There are several aspects to the old Shorewall Ping management:<br>
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<ol>
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<li>The <b>noping</b> and <b>filterping </b>interface options in <a
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href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a>.</li>
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<li>The <b>FORWARDPING</b> option in<a href="Documentation.htm#Conf">
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/etc/shorewall/shorewall.conf</a>.</li>
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<li>Explicit rules in <a href="Documentation.htm#Rules">/etc/shorewall/rules</a>.</li>
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</ol>
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There are two cases to consider:<br>
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<ol>
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<li>Ping requests addressed to the firewall itself; and</li>
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<li>Ping requests being forwarded to another system. Included here are
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all cases of packet forwarding including NAT, DNAT rule, Proxy ARP and simple
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routing.</li>
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</ol>
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These cases will be covered separately.<br>
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<h3>Ping Requests Addressed to the Firewall Itself</h3>
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For ping requests addressed to the firewall, the sequence is as follows:<br>
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<ol>
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<li>If neither <b>noping</b> nor <b>filterping </b>are specified for
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the interface that receives the ping request then the request will be responded
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to with an ICMP echo-reply.</li>
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<li>If <b>noping</b> is specified for the interface that receives the
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ping request then the request is ignored.</li>
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<li>If <b>filterping </b>is specified for the interface then the request
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is passed to the rules/policy evaluation.</li>
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</ol>
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<h3>Ping Requests Forwarded by the Firewall</h3>
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These requests are <b>always</b> passed to rules/policy evaluation.<br>
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<h3>Rules Evaluation</h3>
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Ping requests are ICMP type 8. So the general rule format is:<br>
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<br>
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<i>Target Source
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Destination </i>icmp 8<br>
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<br>
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Example 1. Accept pings from the net to the dmz (pings are responded to
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with an ICMP echo-reply):<br>
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<br>
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ACCEPT net dmz
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icmp 8<br>
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<br>
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Example 2. Drop pings from the net to the firewall<br>
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<br>
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DROP net fw
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icmp 8<br>
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<h3>Policy Evaluation</h3>
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If no applicable rule is found, then the policy for the source to the destination
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is applied.<br>
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<ol>
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<li>If the relevant policy is ACCEPT then the request is responded to
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with an ICMP echo-reply.</li>
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<li>If <b>FORWARDPING</b> is set to Yes in /etc/shorewall/shorewall.conf
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then the request is responded to with an ICMP echo-reply.</li>
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<li>Otherwise, the relevant REJECT or DROP policy is used and the request
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is either rejected or simply ignored.</li>
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</ol>
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<p><font size="2">Updated 1/21/2003 - <a href="support.htm">Tom Eastep</a>
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</font></p>
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<p><a href="copyright.htm"><font size="2">Copyright</font> © <font
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size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a></p>
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<br>
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<br>
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<br>
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</body>
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</html>
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