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624 lines
20 KiB
HTML
624 lines
20 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>Shorewall and Aliased Interfaces</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">Shorewall and Aliased Interfaces</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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<h2>Background</h2>
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The traditional net-tools contain a program called <i>ifconfig</i>
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which is used to configure network devices. ifconfig introduced the concept
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of <i>aliased </i>or <i>virtial </i>interfaces. These virtual interfaces
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have names of the form <i>interface</i>:<i>integer </i>(e.g., eth0:0) and
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ifconfig treats them more or less like real interfaces.<br>
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<br>
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Example:<br>
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<pre>[root@gateway root]# ifconfig eth0:0<br>eth0:0 Link encap:Ethernet HWaddr 02:00:08:3:FA:55<br> inet addr:206.124.146.178 Bcast:206.124.146.255 Mask:255.255.255.0<br> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1<br> Interrupt:11 Base address:0x2000<br>[root@gateway root]# <br></pre>
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The ifconfig utility is being gradually phased out in favor of the <i>ip</i>
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utility which is part of the <i>iproute </i>package. The ip utility does
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not use the concept of aliases or virtual interfaces but rather treats
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additional addresses on an interface as objects. The ip utility does provide
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for interaction with ifconfig in that it allows addresses to be <i>labeled
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</i>and labels may take the form of ipconfig virtual interfaces.<br>
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<br>
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Example:<br>
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<br>
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<pre>[root@gateway root]# ip addr show dev eth0<br>2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc htb qlen 100<br> link/ether 02:00:08:e3:fa:55 brd ff:ff:ff:ff:ff:ff<br> inet 206.124.146.176/24 brd 206.124.146.255 scope global eth0<br> inet 206.124.146.178/24 brd 206.124.146.255 scope global secondary eth0:0<br>[root@gateway root]# <br></pre>
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Note that one <u>cannot</u> type "ip addr show dev eth0:0" because
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"eth0:0" is a label for a particular address rather than a device name.<br>
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<pre>[root@gateway root]# ip addr show dev eth0:0<br>Device "eth0:0" does not exist.<br>[root@gateway root]#<br></pre>
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The iptables program doesn't support virtual interfaces in either it's
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"-i" or "-o" command options; as a consequence, Shorewall does not allow
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them to be used in the /etc/shorewall/interfaces file.<br>
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<br>
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<h2>So how do I handle more than one address on an interface?</h2>
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The answer depends on what you are trying to do with the interfaces.
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In the sub-sections that follow, we'll take a look at common scenarios.<br>
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<h3>Separate Rules</h3>
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If you need to make a rule for traffic to/from the firewall itself that
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only applies to a particular IP address, simply qualify the $FW zone with
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the IP address.<br>
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<br>
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Example (allow SSH from net to eth0:0 above):<br>
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<br>
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<blockquote>
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<table cellpadding="2" border="1" cellspacing="0">
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<tbody>
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<tr>
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<td valign="top"><b>ACTION<br>
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</b></td>
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<td valign="top"><b>SOURCE<br>
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</b></td>
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<td valign="top"><b>DESTINATION<br>
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</b></td>
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<td valign="top"><b>PROTOCOL<br>
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</b></td>
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<td valign="top"><b>PORT(S)<br>
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</b></td>
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<td valign="top"><b>SOURCE PORT(S)<br>
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</b></td>
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<td valign="top"><b>ORIGINAL DESTINATION<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">ACCEPT<br>
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</td>
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<td valign="top">net<br>
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</td>
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<td valign="top">fw:206.124.146.178<br>
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</td>
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<td valign="top">tcp<br>
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</td>
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<td valign="top">22<br>
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</td>
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<td valign="top"><br>
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</td>
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<td valign="top"><br>
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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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</blockquote>
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<h3>DNAT</h3>
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Suppose that I had set up eth0:0 as above and I wanted to port forward
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from that virtual interface to a web server running in my local zone at
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192.168.1.3. That is accomplised by a single rule in the /etc/shorewall/rules
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file:<br>
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<br>
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<blockquote>
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<table cellpadding="2" border="1" cellspacing="0">
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<tbody>
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<tr>
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<td valign="top"><b>ACTION<br>
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</b></td>
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<td valign="top"><b>SOURCE<br>
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</b></td>
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<td valign="top"><b>DESTINATION<br>
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</b></td>
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<td valign="top"><b>PROTOCOL<br>
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</b></td>
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<td valign="top"><b>PORT(S)<br>
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</b></td>
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<td valign="top"><b>SOURCE PORT(S)<br>
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</b></td>
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<td valign="top"><b>ORIGINAL DESTINATION<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">DNAT<br>
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</td>
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<td valign="top">net<br>
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</td>
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<td valign="top">loc:192.168.1.3<br>
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</td>
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<td valign="top">tcp<br>
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</td>
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<td valign="top">80<br>
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</td>
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<td valign="top">-<br>
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</td>
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<td valign="top">206.124.146.178<br>
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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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</blockquote>
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<h3>SNAT</h3>
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If you wanted to use eth0:0 as the IP address for outbound connections
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from your local zone (eth1), then in /etc/shorewall/masq:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>SUBNET<br>
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</b></td>
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<td valign="top"><b>ADDRESS<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">eth0<br>
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</td>
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<td valign="top">eth1<br>
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</td>
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<td valign="top">206.124.146.178<br>
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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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</blockquote>
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Shorewall can create the alias (additional address) for you if you
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set ADD_SNAT_ALIASES=Yes in /etc/shorewall/shorewall.conf. Beginning with
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Shorewall 1.3.14, Shorewall can actually create the "label" (virtual interface)
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so that you can see the created address using ifconfig. In addition to
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setting ADD_SNAT_ALIASES=Yes, you specify the virtual interface name in
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the INTERFACE column as follows:<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>SUBNET<br>
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</b></td>
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<td valign="top"><b>ADDRESS<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">eth0:0<br>
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</td>
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<td valign="top">eth1<br>
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</td>
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<td valign="top">206.124.146.178<br>
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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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</blockquote>
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<h3>STATIC NAT</h3>
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If you wanted to use static NAT to link eth0:0 with local address 192.168.1.3,
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you would have the following in /etc/shorewall/nat:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>EXTERNAL<br>
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</b></td>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>INTERNAL<br>
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</b></td>
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<td valign="top"><b>ALL INTERFACES<br>
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</b></td>
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<td valign="top"><b>LOCAL<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">206.124.146.178<br>
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</td>
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<td valign="top">eth0<br>
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</td>
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<td valign="top">192.168.1.3<br>
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</td>
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<td valign="top">no<br>
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</td>
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<td valign="top">no<br>
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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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</blockquote>
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Shorewall can create the alias (additional address) for you if you
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set ADD_IP_ALIASES=Yes in /etc/shorewall/shorewall.conf. Beginning with
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Shorewall 1.3.14, Shorewall can actually create the "label" (virtual interface)
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so that you can see the created address using ifconfig. In addition to
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setting ADD_IP_ALIASES=Yes, you specify the virtual interface name in
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the INTERFACE column as follows:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>EXTERNAL<br>
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</b></td>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>INTERNAL<br>
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</b></td>
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<td valign="top"><b>ALL INTERFACES<br>
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</b></td>
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<td valign="top"><b>LOCAL<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">206.124.146.178<br>
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</td>
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<td valign="top">eth0:0<br>
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</td>
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<td valign="top">192.168.1.3<br>
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</td>
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<td valign="top">no<br>
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</td>
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<td valign="top">no<br>
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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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</blockquote>
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In either case, to create rules that pertain only to this NAT pair,
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you simply qualify the local zone with the internal IP address.<br>
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<br>
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Example: You want to allow SSH from the net to 206.124.146.178 a.k.a.
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192.168.1.3.<br>
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<br>
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<blockquote>
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<table cellpadding="2" border="1" cellspacing="0">
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<tbody>
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<tr>
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<td valign="top"><b>ACTION<br>
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</b></td>
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<td valign="top"><b>SOURCE<br>
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</b></td>
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<td valign="top"><b>DESTINATION<br>
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</b></td>
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<td valign="top"><b>PROTOCOL<br>
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</b></td>
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<td valign="top"><b>PORT(S)<br>
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</b></td>
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<td valign="top"><b>SOURCE PORT(S)<br>
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</b></td>
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<td valign="top"><b>ORIGINAL DESTINATION<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">ACCEPT<br>
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</td>
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<td valign="top">net<br>
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</td>
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<td valign="top">loc:192.168.1.3<br>
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</td>
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<td valign="top">tcp<br>
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</td>
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<td valign="top">22<br>
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</td>
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<td valign="top"><br>
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</td>
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<td valign="top"><br>
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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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</blockquote>
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<h3>MULTIPLE SUBNETS</h3>
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Sometimes multiple IP addresses are used because there are multiple
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subnetworks configured on a LAN segment. This technique does not provide
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for any security between the subnetworks if the users of the systems have
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administrative privileges because in that case, the users can simply manipulate
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their system's routing table to bypass your firewall/router. Nevertheless,
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there are cases where you simply want to consider the LAN segment itself
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as a zone and allow your firewall/router to route between the two subnetworks.<br>
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<br>
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Example 1: Local interface eth1 interfaces to 192.168.1.0/24
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and 192.168.20.0/24. The primary IP address of eth1 is 192.168.1.254 and
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eth1:0 is 192.168.20.254. You want to simply route all requests between
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the two subnetworks.<br>
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<h4>If you are running Shorewall 1.4.1 or Later</h4>
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In /etc/shorewall/interfaces:<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>ZONE<br>
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</b></td>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>BROADCAST<br>
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</b></td>
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<td valign="top"><b>OPTIONS<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">-<br>
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</td>
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<td valign="top">eth1<br>
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</td>
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<td valign="top">192.168.1.255,192.168.20.255<br>
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</td>
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<td valign="top"><br>
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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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</blockquote>
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In /etc/shorewall/hosts:<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>ZONE<br>
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</b></td>
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<td valign="top"><b>HOSTS<br>
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</b></td>
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<td valign="top"><b>OPTIONS<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">loc<br>
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</td>
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<td valign="top">eth1:192.168.1.0/24<br>
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</td>
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<td valign="top"><br>
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</td>
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</tr>
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<tr>
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<td valign="top">loc<br>
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</td>
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<td valign="top">eth1:192.168.20.0/24<br>
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</td>
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<td valign="top"><br>
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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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</blockquote>
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Note that you do NOT need any entry in /etc/shorewall/policy as Shorewall
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1.4.1 and later releases default to allowing intra-zone traffic.<br>
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<h4>If you are running Shorewall 1.4.0 or earlier<br>
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</h4>
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In /etc/shorewall/interfaces:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>ZONE<br>
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</b></td>
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<td valign="top"><b>INTERFACE<br>
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</b></td>
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<td valign="top"><b>BROADCAST<br>
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</b></td>
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<td valign="top"><b>OPTIONS<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">loc<br>
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</td>
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<td valign="top">eth1<br>
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</td>
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<td valign="top">192.168.1.255,192.168.20.255<br>
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</td>
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<td valign="top">Note 1:<br>
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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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</blockquote>
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Note 1: If you are running Shorewall 1.3.10 or earlier then you must
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specify the <b>multi</b> option.<br>
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<br>
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In /etc/shorewall/policy:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>SOURCE<br>
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</b></td>
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<td valign="top"><b>DESTINATION<br>
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</b></td>
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<td valign="top"><b>POLICY<br>
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</b></td>
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<td valign="top"><b>LOG LEVEL<br>
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</b></td>
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<td valign="top"><b>BURST:LIMIT<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">loc<br>
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</td>
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<td valign="top">loc<br>
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</td>
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<td valign="top">ACCEPT<br>
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</td>
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<td valign="top"><br>
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</td>
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<td valign="top"><br>
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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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</blockquote>
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Example 2: Local interface eth1 interfaces to 192.168.1.0/24 and 192.168.20.0/24.
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The primary IP address of eth1 is 192.168.1.254 and eth1:0 is 192.168.20.254.
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You want to make these subnetworks into separate zones and control the
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access between them (the users of the systems do not have administrative
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privileges).<br>
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<br>
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In /etc/shorewall/zones:<br>
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<br>
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<blockquote>
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<table cellpadding="2" cellspacing="0" border="1">
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<tbody>
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<tr>
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<td valign="top"><b>ZONE<br>
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</b></td>
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<td valign="top"><b>DISPLAY<br>
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</b></td>
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<td valign="top"><b>DESCRIPTION<br>
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</b></td>
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</tr>
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<tr>
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<td valign="top">loc<br>
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</td>
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<td valign="top">Local<br>
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</td>
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<td valign="top">Local Zone 1<br>
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</td>
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</tr>
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<tr>
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<td valign="top">loc2<br>
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</td>
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<td valign="top">Local2<br>
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</td>
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<td valign="top">Local Zone 2<br>
|
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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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</blockquote>
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In /etc/shorewall/interfaces:<br>
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<br>
|
|
|
|
<blockquote>
|
|
<table cellpadding="2" cellspacing="0" border="1">
|
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<tbody>
|
|
<tr>
|
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<td valign="top"><b>ZONE<br>
|
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</b></td>
|
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<td valign="top"><b>INTERFACE<br>
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|
</b></td>
|
|
<td valign="top"><b>BROADCAST<br>
|
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</b></td>
|
|
<td valign="top"><b>OPTIONS<br>
|
|
</b></td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">-<br>
|
|
</td>
|
|
<td valign="top">eth1<br>
|
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</td>
|
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<td valign="top">192.168.1.255,192.168.20.255<br>
|
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</td>
|
|
<td valign="top">Note 1:<br>
|
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</td>
|
|
</tr>
|
|
|
|
</tbody>
|
|
</table>
|
|
<br>
|
|
</blockquote>
|
|
Note 1: If you are running Shorewall 1.3.10 or earlier then you must
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|
specify the <b>multi</b> option.<br>
|
|
<br>
|
|
In /etc/shorewall/hosts:<br>
|
|
|
|
<blockquote>
|
|
<table cellpadding="2" cellspacing="0" border="1">
|
|
<tbody>
|
|
<tr>
|
|
<td valign="top"><b>ZONE<br>
|
|
</b></td>
|
|
<td valign="top"><b>HOSTS<br>
|
|
</b></td>
|
|
<td valign="top"><b>OPTIONS<br>
|
|
</b></td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">loc<br>
|
|
</td>
|
|
<td valign="top">eth1:192.168.1.0/24<br>
|
|
</td>
|
|
<td valign="top"><br>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">loc2<br>
|
|
</td>
|
|
<td valign="top">eth1:192.168.20.0/24<br>
|
|
</td>
|
|
<td valign="top"><br>
|
|
</td>
|
|
</tr>
|
|
|
|
</tbody>
|
|
</table>
|
|
<br>
|
|
</blockquote>
|
|
In /etc/shorewall/rules, simply specify ACCEPT rules for the traffic
|
|
that you want to permit.<br>
|
|
<br>
|
|
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<p align="left"><font size="2">Last Updated 5/8/2003 A - <a
|
|
href="support.htm">Tom Eastep</a></font></p>
|
|
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|
<p><a href="copyright.htm"><font size="2">Copyright</font> ©
|
|
<font size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
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<br>
|
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</p>
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<br>
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<br>
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<br>
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