holm/shorewall_code
1
0
Fork 0
forked from extern/shorewall_code
Code Pull Requests Activity
e7d83205db
shorewall_code/Shorewall-docs/Documentation.htm
teastep c68ecd14e7 Shorewall-1.4.1 
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@519 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
2003-03-23 18:47:54 +00:00

3803 lines
149 KiB
HTML
Raw Blame History

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=windows-1252">
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<title>Shorewall 1.4 Documentation</title>
<base target="_self">
<meta name="Microsoft Theme" content="none, default">
<meta name="Microsoft Border" content="none, default">
<meta name="author" content="Tom Eastep">
</head>
<body>
<table border="0" cellpadding="0" cellspacing="0"
style="border-collapse: collapse;" width="100%" id="AutoNumber4"
bgcolor="#400169" height="90">
<tbody>
<tr>
<td width="100%">
<h1 align="center"><font color="#ffffff">Shorewall 1.4 Reference</font></h1>
</td>
</tr>
</tbody>
</table>
<h2 align="center">This documentation is intended primarily for reference.
Step-by-step instructions for configuring Shorewall
in common setups may be found in the <a
href="shorewall_quickstart_guide.htm">QuickStart Guides</a>.</h2>
<h2>Components</h2>
<p>Shorewall consists of the following components: </p>
<ul>
<li><b><a href="#Variables">params</a></b>
-- a parameter file installed in /etc/shorewall that can
be used to establish the values of shell variables for use
in other files.</li>
<li><b> <a href="#Conf">shorewall.conf</a></b>
-- a parameter file installed in /etc/shorewall that
is used to set several firewall parameters.</li>
<li><b> <a href="#Zones">zones</a></b>
- a parameter file installed in /etc/shorewall that defines
a network partitioning into "zones"</li>
<li><b> <a href="#Policy">policy</a></b>
-- a parameter file installed in /etc/shorewall/ that
establishes overall firewall policy.</li>
<li><b> <a href="#Rules">rules</a>
</b> -- a parameter file installed in /etc/shorewall and
used to express firewall rules that are exceptions to
the high-level policies established in /etc/shorewall/policy.</li>
<li><b><a href="#Blacklist">blacklist</a>
-- </b>a parameter file installed in /etc/shorewall and
used to list blacklisted IP/subnet/MAC addresses.</li>
<li><b><a href="#ECN">ecn</a></b> -- a parameter file installed in /etc/shorewall
and used to selectively disable Explicit Congestion Notification (ECN - RFC
3168).<br>
</li>
<li><b> functions</b> -- a set of shell
functions used by both the firewall and shorewall shell
programs. Installed in /etc/shorewall prior to version 1.3.2,
in /var/lib/shorewall in version s 1.3.2-1.3.8 and in /usr/lib/shorewall
in later versions.</li>
<li><b> <a href="#modules">modules</a></b>
-- a parameter file installed in /etc/shorewall and that
specifies kernel modules and their parameters. Shorewall will
automatically load the modules specified in this file.</li>
<li><a
href="#TOS"><b> tos</b> </a>-- a parameter file installed in
/etc/shorewall that is used to specify how the Type of Service
(TOS) field in packets is to be set.<br>
</li>
<li><b><a href="#Scripts">common.def</a></b>
-- a parameter file installed in in /etc/shorewall that
defines firewall-wide rules that are applied before a DROP
or REJECT policy is applied.</li>
<li><b> <a href="#Interfaces">interfaces</a>
</b> -- a parameter file installed in /etc/shorewall/
and used to describe the interfaces on the firewall system.</li>
<li><a href="#Hosts"><b> hosts</b>
</a>-- a parameter file installed in /etc/shorewall/ and
used to describe individual hosts or subnetworks in
zones.</li>
<li><b><a href="#Maclist">maclist</a> </b>--
a parameter file installed in /etc/shorewall and used to verify
the MAC address (and possibly also the IP address(es)) of devices.<br>
</li>
<li><b> <a href="#Masq">masq</a></b>
- This file also describes IP masquerading under Shorewall
and is installed in /etc/shorewall.</li>
<li><b><a
href="shorewall_firewall_structure.htm">firewall</a></b> -- a shell
program that reads the configuration files in /etc/shorewall
and configures your firewall. This file is installed
in your init.d directory (/etc/rc.d/init.d ) where it
is renamed <i>shorewall.</i> /etc/shorewall/firewall (/var/lib/shorewall/firewall
in versions 1.3.2-1.3.8 and /usr/lib/shorewall/firewall in 1.3.9
and later) is a symbolic link to this program.</li>
<li><b> <a href="#NAT">nat</a></b>
-- a parameter file in /etc/shorewall used to define <a
href="#NAT"> static NAT</a> .</li>
<li><b> <a href="#ProxyArp">proxyarp</a></b>
-- a parameter file in /etc/shorewall used to define <a
href="#ProxyArp"> Proxy Arp</a> .</li>
<li><b><a href="#rfc1918">rfc1918</a></b>
-- a parameter file in /etc/shorewall used to define the treatment
of packets under the <a href="#Interfaces">norfc1918 interface
option</a>.</li>
<li><b><a href="#Routestopped">routestopped</a></b>
-- a parameter file in /etc/shorewall used to define those
hosts that can access the firewall when Shorewall is stopped.</li>
<li><a
href="traffic_shaping.htm#tcrules"><b>tcrules</b> </a>--
a parameter file in /etc/shorewall used to define rules for classifying
packets for <a href="traffic_shaping.htm">Traffic Shaping/Control</a>.</li>
<li><b> <a href="#Tunnels">tunnels</a></b>
-- a parameter file in /etc/shorewall used to define
IPSec tunnels.</li>
<li><b> <a href="#Starting">shorewall</a>
</b> -- a shell program (requiring a Bourne shell or
derivative) used to control and monitor
the firewall. This should be placed in /sbin or in /usr/sbin
(the install.sh script and the rpm install this file
in /sbin).</li>
<li><b> version</b> -- a file created
in /etc/shorewall/ (/var/lib/shorewall in version
1.3.2-1.3.8 and /usr/lib/shorewall beginning in version 1.3.9)
that describes the version of Shorewall installed
on your system.</li>
</ul>
<h2><a name="Variables"></a> /etc/shorewall/params</h2>
<p>You may use the file /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>
<pre><font face="Courier"> NET_IF=eth0<br> NET_BCAST=130.252.100.255<br> NET_OPTIONS=blacklist,norfc1918</font></pre>
<p>Example (/etc/shorewall/interfaces record):</p>
<pre> <font face="Courier">net $NET_IF $NET_BCAST $NET_OPTIONS</font></pre>
<p>The result will be the same as if the record had been written</p>
<pre> <font face="Courier">net eth0 130.252.100.255 blacklist,norfc1918</font></pre>
<p>Variables may be used anywhere in the other configuration
files.</p>
<h2><b><a name="Zones"></a> </b>/etc/shorewall/zones</h2>
<p>This file is used to define the network zones. There is one entry
in /etc/shorewall/zones for each zone; Columns in an entry
are:</p>
<ul>
<li><b> ZONE</b> - short name for the
zone. The name should be 5 characters or less in length
and consist of lower-case letters or numbers. Short names must
begin with a letter and the name assigned to the firewall is
reserved for use by Shorewall itself. Note that the output produced
by iptables is much easier to read if you select short names
that are three characters or less in length. The name "all"
may not be used as a zone name nor may the zone name assigned to
the firewall itself via the FW variable in <a href="#Conf">/etc/shorewall/shorewall.conf</a>.</li>
<li><b> DISPLAY</b> - The name of the
zone as displayed during Shorewall startup.</li>
<li><b> COMMENTS</b> - Any comments
that you want to make about the zone. Shorewall ignores
these comments.</li>
</ul>
<p>The /etc/shorewall/zones file released with Shorewall is as follows:</p>
<table border="1" style="border-collapse: collapse;" cellpadding="2">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> DISPLAY</b></td>
<td><b> COMMENTS</b></td>
</tr>
<tr>
<td>net</td>
<td>Net</td>
<td>Internet</td>
</tr>
<tr>
<td>loc</td>
<td>Local</td>
<td>Local networks</td>
</tr>
<tr>
<td>dmz</td>
<td>DMZ</td>
<td>Demilitarized zone</td>
</tr>
</tbody>
</table>
<p>You may add, delete and modify entries in the /etc/shorewall/zones file
as desired so long as you have at least one zone defined.</p>
<p><b><font size="5" color="#ff0000"> Warning 1: </font><font
color="#ff0000"> If you rename or delete a zone, you should perform "shorewall
stop; shorewall start" to install the change rather than
"shorewall restart".</font></b></p>
<p><b><font size="5" color="#ff0000">Warning 2: </font><font
color="#ff0000">The order of entries in the /etc/shorewall/zones file is
significant <a href="#Nested">in some cases</a>.</font></b></p>
<h2><font color="#660066"><a name="Interfaces"></a> </font>/etc/shorewall/interfaces</h2>
<p>This file is used to tell the firewall which of your firewall's network
interfaces are connected to which zone. There will be
one entry in /etc/shorewall/interfaces for each of your interfaces.
Columns in an entry are:</p>
<ul>
<li><b> ZONE</b> - A zone defined in
the <a href="#Zones">/etc/shorewall/zones</a> file or
"-". If you specify "-", you must use the <a href="#Hosts">
/etc/shorewall/hosts</a> file to define the zones
accessed via this interface.</li>
<li><b> INTERFACE</b> - the name of
the interface (examples: eth0, ppp0, ipsec+). Each interface
can be listed on only one record in this file. <font
color="#ff0000"><b>D</b><b>O NOT INCLUDE THE LOOPBACK INTERFACE
(lo) IN THIS FILE!!!</b></font></li>
<li><b> BROADCAST</b> - the broadcast
address(es) for the sub-network(s) attached to the interface.
This should be left empty for P-T-P interfaces (ppp*, ippp*);
if you need to specify options for such an interface, enter "-"
in this column. If you supply the special value "detect" in this
column, the firewall will automatically determine the broadcast
address. In order to use "detect":
<ul>
<li>the
interface must be up before you start your firewall</li>
<li>the interface must only be attached
to a single sub-network (i.e., there must have a single broadcast
address). </li>
</ul>
</li>
<li><b> OPTIONS</b> - a comma-separated
list of options. Possible options include:
<p> <b>tcpflags </b>(added in version 1.3.11) - This option causes Shorewall
to make sanity checks on the header flags in TCP packets arriving on this
interface. Checks include Null flags, SYN+FIN, SYN+RST and FIN+URG+PSH; these
flag combinations are typically used for "silent" port scans. Packets failing
these checks are logged according to the TCP_FLAGS_LOG_LEVEL option in<a
href="#Conf"> /etc/shorewall/shorewall.conf</a> and are disposed of according
to the TCP_FLAGS_DISPOSITION option.<br>
<b><br>
blacklist</b> - This option causes incoming packets
on this interface to be checked against the <a
href="#Blacklist">blacklist</a>.<b><br>
<br>
dhcp</b> - The interface is assigned an
IP address via DHCP or is used by a DHCP server running
on the firewall. The firewall will be configured to allow
DHCP traffic to and from the interface even when the firewall
is stopped. You may also wish to use this option if you have a
static IP but you are on a LAN segment that has a lot of Laptops
that use DHCP and you select the <b>norfc1918 </b>option
(see below).</p>
<p> <b>norfc1918</b> - Packets arriving on this interface and that
have a source address that is reserved in RFC 1918 or in other
RFCs will be dropped after being optionally logged. If <a
href="#Conf">packet mangling is enabled in /etc/shorewall/shorewall.conf</a>
, then packets arriving on this interface that have a
destination address that is reserved by one of these RFCs will
also be logged and dropped.<br>
<br>
Addresses blocked by the standard <a
href="#rfc1918"> <b>rfc1918 </b>file</a> include those
addresses reserved by RFC1918 plus other ranges reserved by
the IANA or by other RFCs.</p>
<p> Beware that as IPv4 addresses become in increasingly short supply,
ISPs are beginning to use RFC 1918 addresses within their
own infrastructure. Also, many cable and DSL "modems" have
an RFC 1918 address that can be used through a web browser for
management and monitoring functions. If you want to specify
<b>norfc1918</b> on your external interface but need to allow
access to certain addresses from the above list, see <a
href="FAQ.htm#faq14">FAQ 14.</a></p>
<p> <b> routefilter</b> - Invoke the Kernel's route filtering
(anti-spoofing) facility on this interface. The kernel
will reject any packets incoming on this interface that have
a source address that would be routed outbound through another
interface on the firewall. <font color="#ff0000">Warning:
</font>If you specify this option for an interface then
the interface must be up prior to starting the firewall.</p>
<p> <b>dropunclean</b> - Packets from this interface that
are selected by the 'unclean' match target in iptables will
be <a href="#LogUnclean">optionally logged</a> and then dropped.
<font color="#ff0000"><b>Warning: This feature
requires that UNCLEAN match support be configured in your
kernel, either in the kernel itself or as a module. UNCLEAN
support is broken in some versions of the kernel
but appears to work ok in 2.4.17-rc1.<br>
<br>
Update 12/17/2001: </b></font>The
unclean match patch from 2.4.17-rc1 is
<a href="ftp://ftp.shorewall.net/pub/shorewall/misc/unclean.patch">available
for download</a>. I am currently running
this patch applied to kernel 2.4.16.</p>
<p><font color="#ff0000"><b>Update 12/20/2001: </b></font>I've
seen a number of tcp connection requests
with OPT (020405B4<u>0000080A</u>...) being
dropped in the <i>badpkt</i> chain. This appears to be
a bug in the remote TCP stack whereby it is 8-byte aligning
a timestamp (TCP option 8) but rather than padding
with 0x01 it is padding with 0x00. It's a tough call
whether to deny people access to your servers because
of this rather minor bug in their networking software.
If you wish to disable the check that causes
these connections to be dropped, <a
href="ftp://ftp.shorewall.net/pub/shorewall/misc/unclean1.patch">here's
a kernel patch</a> against 2.4.17-rc2.</p>
<p><b>logunclean </b>- This option works like <b>dropunclean</b>
with the exception that packets selected
by the 'unclean' match target in iptables
are logged <i>but not dropped</i>. The
level at which the packets are logged is determined by
the setting of <a href="#LogUnclean">LOGUNCLEAN</a>
and if LOGUNCLEAN has not been set, "info" is assumed.</p>
<p><b>proxyarp </b>(Added in version 1.3.5) - This option
causes Shorewall to set /proc/sys/net/ipv4/conf/<i>&lt;interface&gt;</i>/proxy_arp
and is used when implementing Proxy
ARP Sub-netting as described at
<a href="http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/">
http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/</a>.
Do <u> not</u> set this option if you are implementing
Proxy ARP through entries in <a href="#ProxyArp">
/etc/shorewall/proxyarp</a>.<br>
<br>
<b>maclist</b> (Added in version 1.3.10)
- If this option is specified, all connection requests from this
interface are subject to <a href="MAC_Validation.html">MAC Verification</a>.
May only be specified for ethernet interfaces.</p>
</li>
</ul>
<p>My recommendations concerning options:<br>
</p>
<ul>
<li>External Interface -- <b>tcpflags,blacklist,norfc1918,routefilter</b></li>
<li>Wireless Interface -- <b>maclist,routefilter,tcpflags</b><br>
</li>
<li>Don't use <b>dropunclean</b> -- It's broken
in my opinion</li>
<li>Use <b>logunclean</b> only when you are trying
to debug a problem</li>
<li>Use <b>dhcp </b>and <b>proxyarp</b> when needed.<br>
</li>
</ul>
<p> </p>
<p>Example 1: You have a conventional firewall setup in which eth0 connects
to a Cable or DSL modem and eth1 connects to your local
network and eth0 gets its IP address via DHCP. You want to
check all packets entering from the internet
against the <a href="#Blacklist">black list</a>. Your /etc/shorewall/interfaces
file would be as follows:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>net</td>
<td>eth0</td>
<td>detect</td>
<td>dhcp,norfc1918,blacklist</td>
</tr>
<tr>
<td>loc</td>
<td>eth1</td>
<td>detect</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p>Example 2: You have a standalone dialup GNU/Linux System. Your /etc/shorewall/interfaces
file would be:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>net</td>
<td>ppp0</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p>Example 3: You have local interface eth1 with two IP
addresses - 192.168.1.1/24 and 192.168.12.1/24</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>loc</td>
<td>eth1</td>
<td>192.168.1.255,192.168.12.255</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<h2><font color="#660066"><a name="Hosts"></a> </font>/etc/shorewall/hosts
Configuration</h2>
<p>For most applications, specifying zones entirely in terms of network
interfaces is sufficient. There may be times though where you need to
define a zone to be a more general collection of hosts. This is the purpose
of the /etc/shorewall/hosts file.</p>
<p><b><font color="#ff0000">WARNING: </font>The only times that you need
entries in /etc/shorewall/hosts are:<br>
</b></p>
<ol>
<li><b>You have more than one zone connecting through a single interface;
or</b></li>
<li><b>You have a zone that has multiple subnetworks that connect through
a single interface and you want the Shorewall box to route traffic between
those subnetworks.</b><br>
</li>
</ol>
<b>IF YOU DON'T HAVE EITHER OF THOSE SITUATIONS THEN DON'T TOUCH THIS FILE!!</b>
<p>Columns in this file are:</p>
<ul>
<li><b> ZONE </b> - A zone defined
in the <a href="#Zones">/etc/shorewall/zones</a> file.</li>
<li><b> HOST(S)</b> - The name of a
network interface followed by a colon (":") followed
by either:</li>
</ul>
<blockquote>
<ol>
<li>An IP address (example
- eth1:192.168.1.3)</li>
<li>A subnet in CIDR notation<i>
</i>(example - eth2:192.168.2.0/24)</li>
</ol>
<p>The interface name much match an entry in /etc/shorewall/interfaces.</p>
</blockquote>
<ul>
<li><b> OPTIONS</b> - A comma-separated
list of option</li>
</ul>
<blockquote>
<p><b>maclist - </b>Added in version 1.3.10. If specified, connection
requests from the hosts specified in this entry are subject to
<a href="MAC_Validation.html">MAC Verification</a>. This option is only
valid for ethernet interfaces.<br>
</p>
</blockquote>
<p>If you don't define any hosts for a zone, the hosts in the zone default
to i0:0.0.0.0/0 , i1:0.0.0.0/0, ... where i0, i1, ...
are the interfaces to the zone.</p>
<p><b><font size="4" color="#ff0000">Note: </font></b> You probably DON'T
want to specify any hosts for your internet zone since the hosts that
you specify will be the only ones that you will be able to access without
adding additional rules.</p>
<p>Example 1:</p>
<p>Your local interface is eth1 and you have two groups of local hosts that
you want to make into separate zones:</p>
<ul>
<li>192.168.1.0/25 </li>
<li>192.168.1.128/</li>
</ul>
<p>Your /etc/shorewall/interfaces file might look like:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>net</td>
<td>eth0</td>
<td>detect</td>
<td>dhcp,norfc1918</td>
</tr>
<tr>
<td>-</td>
<td>eth1</td>
<td>192.168.1.127,192.168.1.255<br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> The '-' in the ZONE column for eth1 tells Shorewall that eth1 interfaces
to multiple zones.</p>
<p> Your /etc/shorewall/hosts file might look like:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica">
</font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> HOST(S)</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>loc1</td>
<td>eth1:192.168.1.0/25</td>
<td> <br>
</td>
</tr>
<tr>
<td>loc2</td>
<td>eth1:192.168.1.128/25</td>
<td><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p>Example 2:</p>
<p>Your local interface is eth1 and you have two groups of local hosts that
you want to consider as one zone and you want Shorewall to route between
them:</p>
<ul>
<li>192.168.1.0/25 </li>
<li>192.168.1.128/25</li>
</ul>
<p> Your /etc/shorewall/interfaces file might look like:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>net</td>
<td>eth0</td>
<td>detect</td>
<td>dhcp,norfc1918</td>
</tr>
<tr>
<td>loc<br>
</td>
<td>eth1</td>
<td>192.168.1.127,192.168.1.255<br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> Your /etc/shorewall/hosts file might look like:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica">
</font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> HOST(S)</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>loc</td>
<td>eth1:192.168.1.0/25</td>
<td> <br>
</td>
</tr>
<tr>
<td>loc</td>
<td>eth1:192.168.1.128/25</td>
<td><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<h4><font color="#660066"><a name="Nested"></a> Nested and Overlapping
Zones</font></h4>
<p> The /etc/shorewall/interfaces and /etc/shorewall/hosts file allow
you to define nested or overlapping zones. Such overlapping/nested zones
are allowed and Shorewall processes zones in the order
that they appear in the /etc/shorewall/zones file. So if you
have nested zones, you want the sub-zone to appear before
the super-zone and in the case of overlapping zones, the rules
that will apply to hosts that belong to both zones is determined
by which zone appears first in /etc/shorewall/zones.</p>
<p> Hosts that belong to more than one zone may be managed by the rules
of all of those zones. This is done through use of the special
<a href="#CONTINUE">CONTINUE policy</a> described below.</p>
<h2><font color="#660066"><a name="Policy"></a>
</font>/etc/shorewall/policy Configuration.</h2>
<p>This file is used to describe the firewall policy regarding establishment
of connections. Connection establishment is described in
terms of <i>clients</i> who initiate connections and <i> servers
</i>who receive those connection requests. Policies defined
in /etc/shorewall/policy describe which zones are allowed
to establish connections with other zones.</p>
<p>Policies established in /etc/shorewall/policy can be viewed as default
policies. If no rule in /etc/shorewall/rules applies to
a particular connection request then the policy from /etc/shorewall/policy
is applied.</p>
<p>Four policies are defined:</p>
<ul>
<li><b> ACCEPT</b> - The connection
is allowed.</li>
<li><b> DROP</b> - The connection request
is ignored.</li>
<li><b> REJECT</b> - The connection
request is rejected with an RST (TCP) or an ICMP destination-unreachable
packet being returned to the client.</li>
<li><b> CONTINUE </b> - The connection
is neither ACCEPTed, DROPped nor REJECTed. CONTINUE may
be used when one or both of the zones named in the entry are
sub-zones of or intersect with another zone. For more information,
see below.</li>
<li><b>NONE</b> - (Added in version 1.4.1) - Shorewall should not set up
any infrastructure for handling traffic from the SOURCE zone to the DEST
zone. When this policy is specified, the <b>LOG LEVEL </b>and <b>BURST:LIMIT
</b>columns must be left blank.<br>
</li>
</ul>
<p> For each policy specified in /etc/shorewall/policy, you can indicate
that you want a message sent to your system log each time
that the policy is applied.</p>
<p> Entries in /etc/shorewall/policy have four columns as follows:</p>
<ol>
<li> <b>
SOURCE</b> - The name of a client zone (a zone defined in the
<a href="#Zones"> /etc/shorewall/zones file</a> , the
<a href="#Conf">name of the firewall zone</a> or "all").</li>
<li> <b>
DEST</b> - The name of a destination zone (a zone defined in
the <a href="#Zones"> /etc/shorewall/zones file</a> , the
<a href="#Conf">name of the firewall zone</a> or "all"). Shorewall
automatically allows all traffic from the firewall to itself so
the <a href="#Conf">name of the firewall zone</a> cannot appear in both
the SOURCE and DEST columns.</li>
<li> <b>
POLICY</b> - The default policy for connection requests from
the SOURCE zone to the DESTINATION zone.</li>
<li> <b>
LOG LEVEL</b> - Optional. If left empty, no log message is
generated when the policy is applied. Otherwise, this column
should contain an integer or name indicating a <a
href="shorewall_logging.html">syslog level</a>.</li>
<li> <b>LIMIT:BURST
</b>- Optional. If left empty, TCP connection requests
from the <b>SOURCE</b> zone to the <b>DEST</b> zone will
not be rate-limited. Otherwise, this column specifies the maximum
rate at which TCP connection requests will be accepted followed
by a colon (":") followed by the maximum burst size that will be
tolerated. Example: <b> 10/sec:40</b> specifies that the maximum
rate of TCP connection requests allowed will be 10 per second and
a burst of 40 connections will be tolerated. Connection requests
in excess of these limits will be dropped.</li>
</ol>
<p> In the SOURCE and DEST columns, you can enter "all" to indicate all
zones. </p>
<p> The policy file installed by default is as follows:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica">
</font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> POLICY</b></td>
<td><b> LOG LEVEL</b></td>
<td><b>LIMIT:BURST</b></td>
</tr>
<tr>
<td>loc</td>
<td>net</td>
<td>ACCEPT</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
<td> <br>
</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>REJECT</td>
<td>info</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> This table may be interpreted as follows:</p>
<ul>
<li>All connection requests from the
local network to hosts on the internet are accepted.</li>
<li>All connection requests originating
from the internet are ignored and logged at level KERNEL.INFO.</li>
<li>All other connection requests are
rejected and logged.</li>
</ul>
<p><b><font size="4" color="#ff0000">WARNING:</font></b></p>
<p><font color="#ff0000"><b> The firewall script processes</b> <b> the
/etc/shorewall/policy file from top to bottom and <u>uses
the first applicable policy that it finds.</u> For example,
in the following policy file, the policy for (loc, loc) connections
would be ACCEPT as specified in the first entry even though the
third entry in the file specifies REJECT.</b></font></p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b>POLICY</b></td>
<td><b>LOG LEVEL</b></td>
<td><b>LIMIT:BURST</b></td>
</tr>
<tr>
<td>loc</td>
<td>all</td>
<td>ACCEPT</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
<td> <br>
</td>
</tr>
<tr>
<td>loc</td>
<td>loc</td>
<td>REJECT</td>
<td>info</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<h4><a name="IntraZone"></a>IntraZone Traffic</h4>
Shorewall allows a zone to be associated with more than one interface or
with multiple networks that interface through a single interface. Beginning
with Shorewall 1.4.1, Shorewall will ACCEPT all traffic from a zone to itself
provided that there is no explicit policy governing traffic from that zone
to itself (an explicit policy does not specify "all" in either the SOURCE
or DEST column) and that there are no rules concerning connections from that
zone to itself. If there is an explicit policy or if there are one or more
rules, then traffic within the zone is handled just like traffic between
zones is.<br>
<p>Any time that you have multiple interfaces associated with a single zone,
you should ask yourself if you really want traffic routed between those interfaces.
Cases where you might not want that behavior are:<br>
</p>
<ol>
<li>Multiple 'net' interfaces to different ISPs. You don't want to route
traffic from one ISP to the other through your firewall.</li>
<li>Multiple VPN clients. You don't necessarily want them to all be able
to communicate between themselves using your gateway/router.<br>
</li>
</ol>
<h4><font color="#660066"><a name="CONTINUE"></a>
The CONTINUE policy</font></h4>
<p> Where zones are <a href="#Nested">nested or overlapping</a> , the
CONTINUE policy allows hosts that are within multiple zones
to be managed under the rules of all of these zones. Let's look
at an example:</p>
<p> /etc/shorewall/zones:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> DISPLAY</b></td>
<td><b> COMMENTS</b></td>
</tr>
<tr>
<td>sam</td>
<td>Sam</td>
<td>Sam's system at home</td>
</tr>
<tr>
<td>net</td>
<td>Internet</td>
<td>The Internet</td>
</tr>
<tr>
<td>loc</td>
<td>Loc</td>
<td>Local Network</td>
</tr>
</tbody>
</table>
</blockquote>
<p> /etc/shorewall/interfaces:</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> INTERFACE</b></td>
<td><b> BROADCAST</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>-</td>
<td>eth0</td>
<td>detect</td>
<td>dhcp,norfc1918</td>
</tr>
<tr>
<td>loc</td>
<td>eth1</td>
<td>detect</td>
<td><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> /etc/shorewall/hosts:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ZONE</b></td>
<td><b> HOST(S)</b></td>
<td><b> OPTIONS</b></td>
</tr>
<tr>
<td>net</td>
<td>eth0:0.0.0.0/0</td>
<td> <br>
</td>
</tr>
<tr>
<td>sam</td>
<td>eth0:206.191.149.197</td>
<td><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> Note that Sam's home system is a member of both the <b>sam</b> zone
and the <b>net</b>
zone and <a href="#Nested"> as described above</a> , that means
that <b>sam</b> must be listed before <b>net</b> in /etc/shorewall/zones.</p>
<p> /etc/shorewall/policy:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font><font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> SOURCE</b></td>
<td><b> DEST</b></td>
<td><b> POLICY</b></td>
<td><b> LOG LEVEL</b></td>
</tr>
<tr>
<td>loc</td>
<td>net</td>
<td>ACCEPT</td>
<td> <br>
</td>
</tr>
<tr>
<td>sam</td>
<td>all</td>
<td>CONTINUE</td>
<td> <br>
</td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>REJECT</td>
<td>info</td>
</tr>
</tbody>
</table>
</blockquote>
<p> The second entry above says that when Sam is the client, connection
requests should first be process under rules where the
source zone is <b>sam</b> and if there is no match then the
connection request should be treated under rules where the source
zone is <b>net</b>. It is important that this policy be listed
BEFORE the next policy (<b>net</b> to <b>all</b>).</p>
<p> Partial /etc/shorewall/rules:</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font><font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>...</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>DNAT</td>
<td>sam</td>
<td>loc:192.168.1.3</td>
<td>tcp</td>
<td>ssh</td>
<td>-</td>
<td> <br>
</td>
</tr>
<tr>
<td>DNAT</td>
<td>net</td>
<td>loc:192.168.1.5</td>
<td>tcp</td>
<td>www</td>
<td>-</td>
<td> <br>
</td>
</tr>
<tr>
<td>...</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p> Given these two rules, Sam can connect to the firewall's internet interface
with ssh and the connection request will be forwarded to
192.168.1.3. Like all hosts in the <b>net</b> zone, Sam can
connect to the firewall's internet interface on TCP port 80
and the connection request will be forwarded to 192.168.1.5.
The order of the rules is not significant.</p>
<p> <a name="Exclude"></a>Sometimes it is necessary to suppress port forwarding
for a sub-zone. For example, suppose that all hosts can
SSH to the firewall and be forwarded to 192.168.1.5 EXCEPT
Sam. When Sam connects to the firewall's external IP, he should
be connected to the firewall itself. Because of the way that Netfilter
is constructed, this requires two rules as follows:</p>
<blockquote>
<p> </p>
<font face="Century Gothic, Arial, Helvetica"> </font><font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>...</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>DNAT</td>
<td>sam</td>
<td>fw</td>
<td>tcp</td>
<td>ssh</td>
<td>-</td>
<td> <br>
</td>
</tr>
<tr>
<td>DNAT</td>
<td>net!sam</td>
<td>loc:192.168.1.3</td>
<td>tcp</td>
<td>ssh</td>
<td>-</td>
<td> <br>
</td>
</tr>
<tr>
<td>...</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p>The first rule allows Sam SSH
access to the firewall. The second
rule says that any clients from the
net zone with the exception of those
in the 'sam' zone should have their
connection port forwarded to
192.168.1.3. If you need to exclude
more than one zone in this way,
you can list
the zones separated by
commas (e.g., net!sam,joe,fred).
This technique also may be used when
the ACTION is REDIRECT.</p>
<h2><font color="#660066"><a name="Rules"></a>
</font>/etc/shorewall/rules</h2>
<p>The /etc/shorewall/rules file defines exceptions to the policies established
in the /etc/shorewall/policy file. There is one entry in
/etc/shorewall/rules for each of these rules. <br>
</p>
<p>Shorewall automatically enables firewall-&gt;firewall traffic over the
loopback interface (lo) -- that traffic cannot be regulated using
rules and any rule that tries to regulate such traffic will generate
a warning and will be ignored.<br>
</p>
<p>Entries in the file have the following columns:</p>
<ul>
<li><b>ACTION</b>
<ul>
<li>ACCEPT, DROP, REJECT, CONTINUE.
These have the same meaning here as in the policy file
above.</li>
<li>DNAT -- Causes the connection request
to be forwarded to the system specified in the DEST column
(port forwarding). "DNAT" stands for "<u>D</u>estination
<u>N</u>etwork <u>A</u>ddress <u>T</u>ranslation"</li>
<li>DNAT- -- The above ACTION (DNAT) generates
two iptables rules: 1) and header-rewriting rule in the Netfilter
'nat' table and; 2) an ACCEPT rule in the Netfilter 'filter' table.
DNAT- works like DNAT but only generates the header-rewriting rule.<br>
</li>
<li>REDIRECT -- Causes the connection
request to be redirected to a port on the local (firewall)
system.</li>
<li>LOG - Log the packet -- requires a syslog level (see below).</li>
</ul>
<p>The ACTION may optionally be followed by ":" and a <a
href="shorewall_logging.html">syslog level</a> (example: REJECT:info).
This causes the packet to be logged at the specified level prior
to being processed according to the specified ACTION. Note: if the
ACTION is LOG then you MUST specify a syslog level.<br>
<br>
The use of DNAT or REDIRECT requires
that you have <a href="#NatEnabled">NAT enabled</a>.<br>
</p>
</li>
<li><b>SOURCE</b> - Describes the source
hosts to which the rule applies.. The contents of this field
must begin with the name of a zone defined in /etc/shorewall/zones,
$FW or "all". If the ACTION is DNAT or REDIRECT, sub-zones may
be excluded from the rule by following the initial zone name with
"!' and a comma-separated list of those sub-zones to be excluded.
There is an <a href="#Exclude">example</a> above.<br>
<br>
If the source is not 'all' then the source
may be further restricted by adding a colon (":") followed
by a comma-separated list of qualifiers. Qualifiers are may
include:
<ul>
<li>An interface name - refers to any
connection requests arriving on the specified interface
(example loc:eth4). Beginning with Shorwall 1.3.9, the interface
name may optionally be followed by a colon (":") and an IP address or
subnet (examples: loc:eth4:192.168.4.22, net:eth0:192.0.2.0/24).</li>
<li>An IP address - refers to a connection
request from the host with the specified address
(example net:155.186.235.151). If the ACTION is DNAT, this must
not be a DNS name.</li>
<li>A MAC Address in <a
href="#MAC">Shorewall format</a>.</li>
<li>A subnet - refers to a connection
request from any host in the specified subnet (example
net:155.186.235.0/24).</li>
</ul>
</li>
<li><b>DEST</b> - Describes the destination
host(s) to which the rule applies. May take most of the forms
described above for SOURCE plus the following two additional
forms:
<ul>
<li>An IP address followed by a colon
and the port <u>number</u> that the server
is listening on (service names from /etc/services are not
allowed - example loc:192.168.1.3:80). <br>
</li>
<li>A single port number (again, service
names are not allowed) -- this form is only allowed
if the ACTION is REDIRECT and refers to a server running on the
firewall itself and listening on the specified port.</li>
</ul>
Restrictions:<br>
<ul>
<li>MAC addresses may not be specified.</li>
<li>In DNAT rules, only an IP address may be given -- DNS names are
not permitted.</li>
<li>You may not specify both an IP address and an interface name
in the DEST column.<br>
</li>
</ul>
</li>
<li><b> PROTO</b> - Protocol. Must
be a protocol name from /etc/protocols, a number or
"all". Specifies the protocol of the connection request.</li>
<li><b> DEST PORT(S)</b> - Port
or port range (&lt;low port&gt;:&lt;high port&gt;) being connected
to. May only be specified if the protocol is tcp, udp
or icmp. For icmp, this column's contents are interpreted
as an icmp type. If you don't want to specify DEST PORT(S) but
need to include information in one of the columns to the right,
enter "-" in this column. You may give a list of ports and/or port
ranges separated by commas. Port numbers may be either integers
or service names from /etc/services.</li>
<li><b> SOURCE</b> <b>PORTS(S) </b>-
May be used to restrict the rule to a particular client port
or port range (a port range is specified as &lt;low port number&gt;:&lt;high
port number&gt;). If you don't want to restrict client ports but
want to specify something in the next column, enter "-" in this
column. If you wish to specify a list of port number or ranges,
separate the list elements with commas (with no embedded white
space). Port numbers may be either integers or service names from
/etc/services.</li>
<li><b>ORIGINAL DEST</b> - This column
may only be non-empty if the ACTION is DNAT or REDIRECT.<br>
<br>
If DNAT or REDIRECT is the ACTION and
the ORIGINAL DEST column is left empty, any connection request
arriving at the firewall from the SOURCE that matches the rule
will be forwarded or redirected. This works fine for connection
requests arriving from the internet where the firewall has
only a single external IP address. When the firewall has multiple
external IP addresses or when the SOURCE is other than the internet,
there will usually be a desire for the rule to only apply to those
connection requests directed to a particular IP address (see
Example 2 below for another usage). That IP address (or a comma-separated
list of such addresses) is specified in the ORIGINAL DEST column.<br>
<br>
The IP address may be optionally followed
by ":" and a second IP address. This latter address, if present,
is used as the source address for packets forwarded to the
server (This is called "Source NAT" or SNAT).<br>
<br>
<b><font color="#ff6633">Note: </font> When using SNAT, it
is a good idea to qualify the source with an IP address or subnet.
Otherwise, it is likely that SNAT will occur on connections other than
those described in the rule. The reason for this is that SNAT occurs in
the Netfilter POSTROUTING hook where it is not possible to restrict
the scope of a rule by incoming interface. <br>
<br>
</b>Example: DNAT loc<u>:192.168.1.0/24</u>
loc:192.168.1.3 tcp www - 206.124.146.179:192.168.1.3<b><br>
<br>
</b>If SNAT is not used (no ":"
and second IP address), the original source address is
used. If you want any destination address to match the rule
but want to specify SNAT, simply use a colon followed by the SNAT
address.</li>
</ul>
<p><b> <font face="Century Gothic, Arial, Helvetica"> <a
name="PortForward"></a> </font>Example 1. </b> You wish to forward all
ssh connection requests from the internet to local system
192.168.1.3. </p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>DNAT</td>
<td>net</td>
<td>loc:192.168.1.3</td>
<td>tcp</td>
<td>ssh</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b> Example 2. </b> You want to redirect all local www connection requests
EXCEPT those
to your own http server
(206.124.146.177) to a Squid
transparent proxy running on the firewall
and listening on port 3128. Squid will of course require access
to remote web servers. This example shows yet
another use for the ORIGINAL
DEST column; here, connection
requests that were NOT
<a
href="#GettingStarted">
(notice the "!")</a> originally
destined to 206.124.146.177 are
redirected to local port 3128.</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>REDIRECT</td>
<td>loc</td>
<td>3128</td>
<td>tcp</td>
<td>www</td>
<td> -<br>
</td>
<td>!206.124.146.177</td>
</tr>
<tr>
<td>ACCEPT</td>
<td>fw</td>
<td>net</td>
<td>tcp</td>
<td>www</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b>Example 3. </b> You want to run a web server at 155.186.235.222 in
your DMZ and have it accessible remotely and locally. the DMZ is managed
by Proxy ARP or by classical sub-netting.</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font><font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>net</td>
<td>dmz:155.186.235.222</td>
<td>tcp</td>
<td>www</td>
<td>-</td>
<td> <br>
</td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc</td>
<td>dmz:155.186.235.222</td>
<td>tcp</td>
<td>www</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b> Example 4. </b> You want to run wu-ftpd on 192.168.2.2 in your masqueraded
DMZ. Your internet interface address is 155.186.235.151
and you want the FTP server to be accessible from the internet
in addition to the local 192.168.1.0/24 and dmz 192.168.2.0/24
subnetworks. Note that since the server is in the 192.168.2.0/24
subnetwork, we can assume that access to the server from that subnet
will not involve the firewall (<a href="FAQ.htm#faq2">but see FAQ
2</a>). Note that unless you
have more than one external
IP address, you can leave
the ORIGINAL DEST column
blank in the first rule. You
cannot leave it blank
in the second rule though
because then <u>all
ftp connections</u>
originating in the local
subnet 192.168.1.0/24 would
be sent to 192.168.2.2 <u>
regardless of the site that
the user was trying to
connect to</u>. That
is clearly not what
you want <img
border="0" src="images/SY00079.gif" width="20" height="20" align="top">
.</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font><font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>DNAT</td>
<td>net</td>
<td>dmz:192.168.2.2</td>
<td>tcp</td>
<td>ftp</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
<tr>
<td>DNAT</td>
<td>loc:192.168.1.0/24</td>
<td>dmz:192.168.2.2</td>
<td>tcp</td>
<td>ftp</td>
<td>-</td>
<td>155.186.235.151</td>
</tr>
</tbody>
</table>
</blockquote>
<p>If you are running wu-ftpd, you should restrict the range of passive
in your /etc/ftpaccess file. I only need a few simultaneous FTP sessions
so I use port range 65500-65535. In /etc/ftpaccess, this
entry is appropriate:</p>
<blockquote>
<p> passive ports 0.0.0.0/0 65500 65534</p>
</blockquote>
<p>If you are running pure-ftpd, you would include "-p 65500:65534" on
the pure-ftpd runline.</p>
<p>The important point here is to ensure that the port range used for FTP
passive connections is unique and will not overlap with
any usage on the firewall system.</p>
<p><b>Example 5. </b>You
wish to allow unlimited
DMZ access to the host
with MAC address
02:00:08:E3:FA:55.</p>
<blockquote> <font
face="Century Gothic, Arial, Helvetica"> </font>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>ACTION</b></td>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b> PROTO</b></td>
<td><b>DEST<br>
PORT(S)</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>ORIGINAL<br>
DEST</b></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc:~02-00-08-E3-FA-55</td>
<td>dmz</td>
<td>all</td>
<td> <br>
</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<b>Example
6.</b> You wish to allow access to the SMTP server in your DMZ
from all zones.<br>
<blockquote>
<table cellpadding="2" cellspacing="0" border="1">
<tbody>
<tr>
<td valign="top"><b>ACTION</b><br>
</td>
<td valign="top"><b>SOURCE<br>
</b></td>
<td valign="top"><b>DEST<br>
</b></td>
<td valign="top"><b>PROTO<br>
</b></td>
<td valign="top"><b>DEST<br>
PORT(S)<br>
</b></td>
<td valign="top"><b>SOURCE<br>
PORT(S)<br>
</b></td>
<td valign="top"><b>ORIGINAL<br>
DEST<br>
</b></td>
</tr>
<tr>
<td valign="top">ACCEPT<br>
</td>
<td valign="top">all<br>
</td>
<td valign="top">dmz<br>
</td>
<td valign="top">tcp<br>
</td>
<td valign="top">25<br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
</tr>
</tbody>
</table>
<br>
Note: When 'all' is used as a source or destination,
intra-zone traffic is not affected. In this example, if there were
two DMZ interfaces then the above rule would NOT enable SMTP traffic
between hosts on these interfaces.<br>
</blockquote>
<b>Example 7 (For advanced users running Shorewall version
1.3.13 or later). </b>From the internet, you with to forward tcp
port 25 directed to 192.0.2.178 and 192.0.2.179 to host 192.0.2.177
in your DMZ. You also want to allow access from the internet directly
to tcp port 25 on 192.0.2.177. <br>
<blockquote>
<table cellpadding="2" cellspacing="0" border="1">
<tbody>
<tr>
<td valign="top"><b>ACTION</b><br>
</td>
<td valign="top"><b>SOURCE<br>
</b></td>
<td valign="top"><b>DEST<br>
</b></td>
<td valign="top"><b>PROTO<br>
</b></td>
<td valign="top"><b>DEST<br>
PORT(S)<br>
</b></td>
<td valign="top"><b>SOURCE<br>
PORT(S)<br>
</b></td>
<td valign="top"><b>ORIGINAL<br>
DEST<br>
</b></td>
</tr>
<tr>
<td valign="top">DNAT-<br>
</td>
<td valign="top">net<br>
</td>
<td valign="top">dmz:192.0.2.177<br>
</td>
<td valign="top">tcp<br>
</td>
<td valign="top">25<br>
</td>
<td valign="top">0<br>
</td>
<td valign="top">192.0.2.178<br>
</td>
</tr>
<tr>
<td valign="top">DNAT-<br>
</td>
<td valign="top">net<br>
</td>
<td valign="top">dmz:192.0.2.177<br>
</td>
<td valign="top">tcp<br>
</td>
<td valign="top">25<br>
</td>
<td valign="top">0<br>
</td>
<td valign="top">192.0.2.179<br>
</td>
</tr>
<tr>
<td valign="top">ACCEPT<br>
</td>
<td valign="top">net<br>
</td>
<td valign="top">dmz:192.0.2.177<br>
</td>
<td valign="top">tcp<br>
</td>
<td valign="top">25<br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
Using "DNAT-" rather than "DNAT" avoids two extra copies
of the third rule from being generated.<br>
<p><a href="ports.htm">Look here for information on other services.</a>
</p>
<h2><a name="Common">
</a>/etc/shorewall/common</h2>
<p>Shorewall allows
definition of rules that
apply between all zones.
By default, these rules
are defined in the file
/etc/shorewall/common.def
but may be modified to
suit individual
requirements. Rather
than modify
/etc/shorewall/common.def,
you should copy that
file to
/etc/shorewall/common
and modify
that file.</p>
<p>The /etc/shorewall/common
file is expected to
contain iptables
commands; rather than
running iptables
directly, you should run
it indirectly using
the Shorewall
function 'run_iptables'.
That way, if iptables
encounters an error, the
firewall will be safely
stopped.</p>
<h2><a name="Masq"></a>
/etc/shorewall/masq</h2>
<p>The /etc/shorewall/masq file is used to define classical IP Masquerading
and Source Network Address Translation (SNAT). There is
one entry in the file for each subnet that you want to masquerade.
In order to make use of this feature, you must have <a
href="#NatEnabled">NAT enabled</a> .</p>
<p> Columns are:</p>
<ul>
<li><b> INTERFACE</b> - The interface
that will masquerade the subnet; this is normally your
internet interface. This interface name can be optionally
qualified by adding ":" and a subnet or host IP. When this
qualification is added, only packets addressed to that host or
subnet will be masqueraded. Beginning with Shorewall version 1.3.14,
if you have set ADD_SNAT_ALIASES=Yes in <a href="#Conf">/etc/shorewall/shorewall.conf</a>,
you can cause Shorewall to create an alias <i>label </i>of the form
<i>interfacename:digit </i>(e.g., eth0:0) by placing that label
in this column. See example 5 below. Alias labels created in this way
allow the alias to be visible to the ipconfig utility. <b>THAT IS
THE ONLY THING THAT THIS LABEL IS GOOD FOR AND IT MAY NOT APPEAR ANYWHERE
ELSE IN YOUR SHOREWALL CONFIGURATION.</b></li>
<li><b> SUBNET</b> - The subnet that
you want to have masqueraded through the INTERFACE. This
may be expressed as a single IP address, a subnet or an interface
name. In the latter instance, the interface must be configured
and started before Shorewall is started as Shorewall will determine
the subnet based on information obtained from the 'ip' utility.
<b><font color="#ff0000">When using Shorewall 1.3.13 or earlier, when
an interface name is specified, Shorewall will only masquerade traffic
from the first subnetwork on the named interface; if the interface interfaces
to more that one subnetwork, you will need to add additional entries
to this file for each of those other subnetworks. Beginning with Shorewall
1.3.14, shorewall will masquerade/SNAT traffic from any host that is routed
through the named interface.</font></b><br>
<br>
The subnet may be optionally followed
by "!' and a comma-separated list of addresses and/or subnets
that are to be excluded from masquerading.</li>
<li><b>ADDRESS</b> - The source address
to be used for outgoing packets. This column is optional and
if left blank, the current primary IP address of the interface
in the first column is used. If you have a static IP on that
interface, listing it here makes processing of output packets
a little less expensive for the firewall. If you specify an address in
this column, it must be an IP address configured on the INTERFACE or
you must have ADD_SNAT_ALIASES enabled in <a href="#Conf">/etc/shorewall/shorewall.conf.</a></li>
</ul>
<p><b> Example 1: </b> You have eth0 connected to a cable modem and eth1
connected to your local subnetwork 192.168.9.0/24. Your
/etc/shorewall/masq file would look like: </p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> INTERFACE</b></td>
<td><b> SUBNET</b></td>
<td><b>ADDRESS</b></td>
</tr>
<tr>
<td>eth0</td>
<td>192.168.9.0/24</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b> Example 2:</b> You have a number of IPSEC tunnels through ipsec0
and you want to masquerade traffic from your 192.168.9.0/24
subnet to the remote subnet 10.1.0.0/16 only.</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> INTERFACE</b></td>
<td><b> SUBNET</b></td>
<td><b>ADDRESS</b></td>
</tr>
<tr>
<td>ipsec0:10.1.0.0/16</td>
<td>192.168.9.0/24</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b> Example 3:</b> You have a DSL line connected on eth0 and a local
network
(192.168.10.0/24)
connected to eth1. You
want all local-&gt;net
connections to use
source address
206.124.146.176.</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> INTERFACE</b></td>
<td><b> SUBNET</b></td>
<td><b>ADDRESS</b></td>
</tr>
<tr>
<td>eth0</td>
<td>192.168.10.0/24</td>
<td>206.124.146.176</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b>Example 4: </b>
Same as example 3
except that you wish
to exclude
192.168.10.44 and
192.168.10.45 from
the SNAT rule.</p>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> INTERFACE</b></td>
<td><b> SUBNET</b></td>
<td><b>ADDRESS</b></td>
</tr>
<tr>
<td>eth0</td>
<td>192.168.10.0/24!192.168.10.44,192.168.10.45</td>
<td>206.124.146.176</td>
</tr>
</tbody>
</table>
</blockquote>
<b>Example 5 (Shorewall version &gt;= 1.3.14): </b>You have a second
IP address (206.124.146.177) assigned to you and wish to use it for
SNAT of the subnet 192.168.12.0/24. You want to give that address the
name eth0:0. You must have ADD_SNAT_ALIASES=Yes in <a href="#Conf">/etc/shorewall/shorewall.conf</a>.<br>
<blockquote>
<table border="1" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> INTERFACE</b></td>
<td><b> SUBNET</b></td>
<td><b>ADDRESS</b></td>
</tr>
<tr>
<td>eth0:0</td>
<td>192.168.12.0/24</td>
<td>206.124.146.177</td>
</tr>
</tbody>
</table>
</blockquote>
<h2><font color="#660066"><b><a name="ProxyArp"></a>
</b></font>/etc/shorewall/proxyarp</h2>
<p>If you want to
use proxy ARP on an
entire sub-network,
I suggest that you
look at
<a
href="http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/">
http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/</a>.
If you decide to use
the technique
described in that
HOWTO, you can set
the proxy_arp flag
for an interface
(/proc/sys/net/ipv4/conf/<i>&lt;interface&gt;</i>/proxy_arp)
by including the <b>
proxyarp</b> option
in the interface's
record in
<a href="#Interfaces">
/etc/shorewall/interfaces</a>.
When using
Proxy ARP
sub-netting, you do
<u>NOT</u> include
any entries in
/etc/shorewall/proxyarp. </p>
<p>The /etc/shorewall/proxyarp file is used to define <a
href="ProxyARP.htm">Proxy ARP</a>. The file is
typically used for
enabling Proxy ARP
on a small set of
systems since you
need one entry
in
this file for each
system using proxy
ARP. Columns are:</p>
<ul>
<li><b> ADDRESS</b> - address of the
system.</li>
<li><b> INTERFACE</b> - the interface
that connects to the system. If the interface is obvious
from the subnetting, you may enter "-" in this column.</li>
<li><b> EXTERNAL</b> - the external
interface that you want to honor ARP requests for the
ADDRESS specified in the first column.</li>
<li><b>HAVEROUTE</b> - If
you already have
a route through
INTERFACE
to ADDRESS,
this
column should
contain
"Yes"
or
"yes".
If you want
Shorewall to add
the route, the
column should
contain
"No"
or
"no".</li>
</ul>
<p><font color="#cc6666"><b>Note: After you have made a change to the /etc/shorewall/proxyarp
file, you may need to flush the ARP cache of all routers
on the LAN segment connected to the interface specified in the
EXTERNAL column of the change/added entry(s). If you are having
problems communicating between an individual host (A) on that
segment and a system whose entry has changed, you may need to
flush the ARP cache on host A as well.</b></font></p>
<p><font color="#cc6666"><b>ISPs typically have ARP configured with long
TTL (hours!) so if your ISPs router has a stale cache entry (as seen using
"tcpdump -nei &lt;external interface&gt; host &lt;IP addr&gt;"), it may
take a long while to time out. I personally have had to contact my ISP
and ask them to delete a stale entry in order to restore a system to working
order after changing my proxy ARP settings. </b></font></p>
<p><b>Example:
</b> You have public IP addresses 155.182.235.0/28. You configure your
firewall as follows:</p>
<ul>
<li>eth0 - 155.186.235.1 (internet connection)</li>
<li>eth1 - 192.168.9.0/24 (masqueraded
local systems)</li>
<li>eth2 - 192.168.10.1 (interface to
your DMZ)</li>
</ul>
<p> In your DMZ, you want to install a Web/FTP server with public address
155.186.235.4. On the Web server, you subnet just like
the firewall's eth0 and you configure 155.186.235.1 as the
default gateway. In your /etc/shorewall/proxyarp file, you
will have:</p>
<blockquote>
<table border="2" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b> ADDRESS</b></td>
<td><b> INTERFACE</b></td>
<td><b> EXTERNAL</b></td>
<td><b>HAVEROUTE</b></td>
</tr>
<tr>
<td>155.186.235.4</td>
<td>eth2</td>
<td>eth0</td>
<td>No</td>
</tr>
</tbody>
</table>
</blockquote>
<p> Note: You may want to configure the servers in your DMZ with a subnet
that is smaller than the subnet of your internet interface.
See the Proxy ARP Subnet Mini HOWTO (<a
href="http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/">http://www.tldp.org/HOWTO/mini/Proxy-ARP-Subnet/</a>)
for details. In this case you will want to place "Yes"
in the HAVEROUTE column.</p>
<p><font color="#ff6633"><b>Warning: </b></font>Do not use Proxy ARP and
FreeS/Wan on the same system unless you are prepared to suffer the consequences.
If you start or restart Shorewall with an IPSEC tunnel active,
the proxied IP addresses are mistakenly assigned to the IPSEC
tunnel device (ipsecX) rather than to the interface that you
specify in the INTERFACE column of /etc/shorewall/proxyarp. I haven't
had the time to debug this problem so I can't say if it is a bug
in the Kernel or in FreeS/Wan. </p>
<p>You <b>might</b> be able to work around this problem using the following
(I haven't tried it):</p>
<p>In /etc/shorewall/init, include:</p>
<p> qt service ipsec stop</p>
<p>In /etc/shorewall/start, include:</p>
<p> qt service ipsec start</p>
<h2><font color="#660066"><b><a name="NAT"></a>
</b></font>/etc/shorewall/nat</h2>
<p>The /etc/shorewall/nat file is used to define static NAT. There is one
entry in the file for each static NAT relationship that
you wish to define. In order to make use of this feature,
you must have <a href="#NatEnabled">NAT enabled</a> .</p>
<p> <font
color="#ff0000">
<b>IMPORTANT: If
all you want to do
is forward ports
to servers behind
your firewall, you
do NOT want to use
static NAT. Port
forwarding
can be accomplished
with
simple entries in
the
<a href="#Rules">
rules file</a>.
Also, in most
cases
<a href="#ProxyArp">
Proxy ARP</a>
provides a
superior solution
to static NAT
because the
internal systems
are accessed
using
the same IP
address internally
and externally.</b></font></p>
<p>Columns in an entry are:</p>
<ul>
<li><b> EXTERNAL</b> - External IP
address - <u>This should NOT be the primary IP address
of the interface named in the next column.</u></li>
<li><b> INTERFACE</b> - Interface that
you want the EXTERNAL IP address to appear on. Beginning
with Shorewall version 1.3.14, if you have set ADD_IP_ALIASES=Yes in
<a href="#Conf">/etc/shorewall/shorewall.conf</a>, <20>you can specify
an alias label of the form <i>interfacename:digit </i>(e.g., eth0:0)
and Shorewall will create the alias with that label. Alias labels created
in this way allow the alias to be visible to the ipconfig utility.
<b>THAT IS THE ONLY THING THAT THIS LABEL IS GOOD FOR AND IT MAY
NOT APPEAR ANYWHERE ELSE IN YOUR SHOREWALL CONFIGURATION.</b><EFBFBD></li>
<li><b> INTERNAL </b> - Internal IP
address.</li>
<li><b>ALL
INTERFACES</b>
- If Yes
or yes (or
left
empty),
NAT
will
be
effective
from all
hosts. If
No or no
then NAT
will be
effective
only
through
the
interface
named in
the
INTERFACE
column.</li>
<li><b>LOCAL</b> - If Yes or yes and
the ALL INTERFACES column contains Yes or yes, NAT will
be effective from the firewall system. <b>Note: </b>For
this to work, you must be running kernel 2.4.19 or later and
iptables 1.2.6a or later and you must have enabled <b>CONFIG_IP_NF_NAT_LOCAL</b>
in your kernel.</li>
</ul>
<p><b><a href="NAT.htm"> Look here for additional information and an example.</a>
</b></p>
<h2><font color="#660066"><a name="Tunnels"></a>
</font>/etc/shorewall/tunnels</h2>
<p> The /etc/shorewall/tunnels file allows you to define IPSec, GRE, IPIP,
<a href="http://openvpn.sourceforge.net/">OpenVPN</a> and PPTP
tunnels with end-points on your firewall. To use ipsec, you must
install version 1.9, 1.91 or the current <a
href="http://www.xs4all.nl/%7Efreeswan/">FreeS/WAN</a> development
snapshot. </p>
<p> Note: For kernels 2.4.4 and above, you will need to use version 1.91
or a development snapshot as patching with version 1.9
results in kernel compilation errors.</p>
<p><b><a href="IPSEC.htm"> Instructions for setting up IPSEC tunnels may
be found here,</a></b> <b><a href="IPIP.htm">instructions
for IPIP and GRE tunnels are here</a></b>, <b><a
href="OPENVPN.html">instructions for OpenVPN tunnels are here</a></b>, and
<b><a href="PPTP.htm">instructions for PPTP tunnels are here</a>.</b></p>
<h2><a name="Conf"></a>/etc/shorewall/shorewall.conf</h2>
<p> This file is used to set the following firewall parameters:</p>
<ul>
<li><b>CLEAR_TC</b> - Added at
version 1.3.13<br>
If this option is set to 'No' then Shorewall won't clear the
current traffic control rules during [re]start. This setting is intended
for use by people that prefer to configure traffic shaping when the
network interfaces come up rather than when the firewall is started.
If that is what you want to do, set TC_ENABLED=Yes and CLEAR_TC=No and
do not supply an /etc/shorewall/tcstart file. That way, your traffic
shaping rules can still use the 'fwmark' classifier based on packet marking
defined in /etc/shorewall/tcrules. If not specified, CLEAR_TC=Yes is assumed.<br>
</li>
<li><b>MARK_IN_FORWARD_CHAIN </b>- Added at version 1.3.12<br>
If your kernel has a FORWARD chain in the mangle table,
you may set MARK_IN_FORWARD_CHAIN=Yes to cause the marking specified
in the <a href="traffic_shaping.htm#tcrules">tcrules file</a> to
occur in that chain rather than in the PREROUTING chain. This permits
you to mark inbound traffic based on its destination address when
SNAT or Masquerading are in use. To determine if your kernel has a FORWARD
chain in the mangle table, use the "/sbin/shorewall show mangle" command;
if a FORWARD chain is displayed then your kernel will support this
option. If this option is not specified or if it is given the empty
value (e.g., MARK_IN_FORWARD_CHAIN="") then MARK_IN_FORWARD_CHAIN=No
is assumed.<br>
</li>
<li><b>RFC1918_LOG_LEVEL - </b>Added at version 1.3.12<br>
This parameter determines the level at which packets
logged under the <a href="Documentation.htm#rfc1918">'norfc1918'
mechanism </a> are logged. The value must be a valid <a
href="shorewall_logging.html">syslog level</a> and if no level is given,
then info is assumed. Prior to Shorewall version 1.3.12, these packets
are always logged at the info level.</li>
<li><b>TCP_FLAGS_DISPOSITION - </b>Added in Version
1.3.11<br>
Determines the disposition of TCP packets that fail
the checks enabled by the <a href="#Interfaces%5C">tcpflags</a>
interface option and must have a value of ACCEPT (accept the packet),
REJECT (send an RST response) or DROP (ignore the packet). If not
set or if set to the empty value (e.g., TCP_FLAGS_DISPOSITION="")
then TCP_FLAGS_DISPOSITION=DROP is assumed.</li>
<li><b>TCP_FLAGS_LOG_LEVEL - </b>Added in Version
1.3.11<br>
Determines the <a href="shorewall_logging.html">syslog
level</a> for logging packets that fail the checks enabled by the
<a href="#Interfaces">tcpflags</a> interface option.The value must
be a valid syslogd log level. If you don't want to log these packets,
set to the empty value (e.g., TCP_FLAGS_LOG_LEVEL="").<br>
</li>
<li><b>MACLIST_DISPOSITION </b>- Added in Version
1.3.10<br>
Determines the disposition of connections requests
that fail <a href="MAC_Validation.html">MAC Verification</a> and
must have the value ACCEPT (accept the connection request anyway), REJECT
(reject the connection request) or DROP (ignore the connection request).
If not set or if set to the empty value (e.g., MACLIST_DISPOSITION="")
then MACLIST_DISPOSITION=REJECT is assumed.</li>
<li><b>MACLIST_LOG_LEVEL </b>- Added in Version
1.3.10<br>
Determines the <a
href="shorewall_logging.html">syslog level</a> for logging connection
requests that fail <a href="MAC_Validation.html">MAC Verification</a>.
The value must be a valid syslogd log level. If you don't want
to log these connection requests, set to the empty value (e.g.,
MACLIST_LOG_LEVEL="").<br>
</li>
<li><b>NEWNOTSYN </b>- Added in Version 1.3.8<br>
When set to "Yes" or "yes", Shorewall will
filter TCP packets that are not part of an established connention
and that are not SYN packets (SYN flag on - ACK flag off). If
set to "No", Shorewall will silently drop such packets. If not
set or set to the empty value (e.g., "NEWNOTSYN="), NEWNOTSYN=No
is assumed.<br>
<br>
If you have a HA setup with failover to another
firewall, you should have NEWNOTSYN=Yes on both firewalls.
You should also select NEWNOTSYN=Yes if you have asymmetric routing.<br>
</li>
<li><b>LOGNEWNOTSYN</b> - Added in Version
1.3.6<br>
Beginning with version 1.3.6, Shorewall
drops non-SYN TCP packets that are not part of an existing
connection. If you would like to log these packets, set LOGNEWNOTSYN
to the <a href="shorewall_logging.html">syslog level</a> at which
you want the packets logged. Example: LOGNEWNOTSYN=ULOG|<br>
<br>
<b>Note: </b>Packets logged under this
option are usually the result of broken remote IP stacks
rather than the result of any sort of attempt to breach your
firewall.</li>
<li><b>DETECT_DNAT_ADDRS</b>
- Added in Version 1.3.4<br>
If set to "Yes" or "yes", Shorewall will detect the IP address(es)
of the interface(es) to the source zone and will include this
(these) address(es) in DNAT rules as the original destination
IP address. If set to "No" or "no", Shorewall will not detect this
(these) address(es) and any destination IP address will match the
DNAT rule. If not specified or empty, "DETECT_DNAT_ADDRS=Yes" is
assumed.<br>
</li>
<li><b></b><b>MULTIPORT</b> - Added in
Version 1.3.2<br>
If set to "Yes" or "yes", Shorewall will
use the Netfilter multiport facility. In order to use
this facility, your kernel must have multiport support
(CONFIG_IP_NF_MATCH_MULTIPORT). When this support is used, Shorewall
will generate a single rule from each record in the /etc/shorewall/rules
file that meets these criteria:<br>
<ul>
<li>No port range(s) specified</li>
<li>Specifies 15 or fewer ports</li>
</ul>
<p>Rules not meeting those criteria will continue to generate an individual
rule for each listed port or port range. </p>
</li>
<li><b>NAT_BEFORE_RULES</b><br>
If set to "No" or "no", port forwarding
rules can override the contents of the <a href="#NAT">/etc/shorewall/nat</a>
file. If set to "Yes" or "yes", port forwarding rules cannot
override static NAT. If not set or set to an empty value, "Yes"
is assumed.</li>
<li><b>FW<br>
</b>This
parameter
specifies the
name of the
firewall zone.
If not set
or if
set to an
empty string,
the value
"fw"
is assumed.</li>
<li><b>SUBSYSLOCK</b><br>
This parameter should be set to
the name of a file that the firewall should create if
it starts successfully and remove when it stops. Creating
and removing this file allows Shorewall to work with your distribution's
initscripts. For RedHat, this should be set to /var/lock/subsys/shorewall.
For Debian, the value is /var/state/shorewall and in LEAF
it is
/var/run/shorwall.
Example: SUBSYSLOCK=/var/lock/subsys/shorewall.</li>
<li><b> STATEDIR</b><br>
This parameter specifies the name
of a directory where Shorewall stores state information.
If the directory doesn't exist when Shorewall starts,
it will create the directory. Example: STATEDIR=/tmp/shorewall.<br>
<br>
<b>NOTE:</b> If you change the STATEDIR
variable while the firewall is running, create the new directory
if necessary then copy the contents of the old directory
to the new directory. </li>
<li><b>MODULESDIR</b><br>
This parameter specifies the directory
where your kernel netfilter modules may be found. If
you leave the variable empty, Shorewall will supply the
value "/lib/modules/`uname -r`/kernel/net/ipv4/netfilter.</li>
<li><b> LOGRATE </b> and <b> LOGBURST</b><br>
These parameters set the match
rate and initial burst size for logged packets. Please
see the iptables man page for a description of the behavior
of these parameters (the iptables option --limit is set by
LOGRATE and --limit-burst is set by LOGBURST). If both parameters
are set empty, no rate-limiting will occur.<br>
<br>
Example:<br>
LOGRATE=10/minute<br>
LOGBURST=5<br>
</li>
<li><b>LOGFILE</b><br>
This parameter
tells the
/sbin/shorewall
program where
to look for
Shorewall
messages
when
processing the
"show
log",
"monitor",
"status"
and
"hits"
commands. If
not assigned
or if assigned
an empty
value,
/var/log/messages
is
assumed.</li>
<li><b>NAT_ENABLED</b><br>
This parameter determines whether
Shorewall supports NAT operations. NAT operations include:<br>
<br>
Static NAT<br>
Port Forwarding<br>
Port Redirection<br>
Masquerading<br>
<br>
If the parameter has no value or
has a value of "Yes" or "yes" then NAT is enabled. If
the parameter has a value of "no" or "No" then NAT is disabled.<br>
</li>
<li><b> MANGLE_ENABLED</b><br>
This parameter determines if packet
mangling is enabled. If the parameter has no value or
has a value of "Yes" or "yes" than packet mangling is enabled.
If the parameter has a value of "no" or "No" then packet mangling
is disabled. If packet mangling is disabled, the /etc/shorewall/tos
file is ignored.<br>
</li>
<li><b> IP_FORWARDING</b><br>
This parameter determines whether
Shorewall enables or disables IPV4 Packet Forwarding
(/proc/sys/net/ipv4/ip_forward). Possible values are:<br>
<br>
On or on - packet forwarding
will be enabled.<br>
Off or off - packet forwarding
will be disabled.<br>
Keep or keep - Shorewall will
neither enable nor disable packet forwarding.<br>
<br>
If this variable is not set or
is given an empty value (IP_FORWARD="") then IP_FORWARD=On
is assumed.<br>
</li>
<li><b>ADD_IP_ALIASES</b><br>
This parameter determines whether
Shorewall automatically adds the
<i>external </i>address(es)
in <a href="#NAT">/etc/shorewall/nat</a> . If the variable
is set to "Yes" or "yes" then Shorewall automatically
adds these aliases. If it is set to "No" or "no", you must
add these aliases yourself using your distribution's network
configuration tools.<br>
<br>
If this variable is not set or is
given an empty value (ADD_IP_ALIASES="") then ADD_IP_ALIASES=Yes
is assumed.</li>
<li><b>ADD_SNAT_ALIASES</b><br>
This parameter determines whether Shorewall
automatically adds the SNAT <i> ADDRESS </i>in <a
href="#Masq">/etc/shorewall/masq</a>. If the variable is set
to "Yes" or "yes" then Shorewall automatically adds these addresses.
If it is set to "No" or "no", you must add these addresses yourself
using your distribution's network configuration tools.<br>
<br>
If this variable is not set or is
given an empty value (ADD_SNAT_ALIASES="") then ADD_SNAT_ALIASES=No
is assumed.<br>
</li>
<li><b>LOGUNCLEAN</b><br>
This parameter
determines the
logging level
of
mangled/invalid
packets
controlled by
the '<a
href="#Unclean">dropunclean
and logunclean</a>'
interface
options. If
LOGUNCLEAN
is
empty
(LOGUNCLEAN=)
then packets
selected by
'dropclean' are
dropped
silently
('logunclean'
packets are
logged
under
the 'info' log
level).
Otherwise,
these packets
are logged at
the specified
level
(Example:
LOGUNCLEAN=debug).</li>
<li><b>BLACKLIST_DISPOSITION</b><br>
This parameter
determines the
disposition of
packets from
blacklisted
hosts. It
may
have the value
DROP if the
packets are to
be dropped or
REJECT if the
packets are to
be replied
with an
ICMP port
unreachable
reply
or a TCP
RST (tcp
only). If you
do not assign
a value or if
you assign an
empty value
then DROP is
assumed.</li>
<li><b>BLACKLIST_LOGLEVEL</b><br>
This paremter
determines if
packets from
blacklisted
hosts are
logged and it
determines
the
syslog level
that they are
to be logged
at. Its value
is a <a
href="shorewall_logging.html">syslog level</a>
(Example:
BLACKLIST_LOGLEVEL=debug).
If you do not
assign a value
or if you
assign an
empty value
then packets
from
blacklisted
hosts are not
logged.</li>
<li><b>CLAMPMSS</b><br>
This parameter
enables the
TCP Clamp MSS
to PMTU
feature of
Netfilter and
is usually
required
when your
internet
connection is
through PPPoE
or PPTP. If
set to
"Yes"
or
"yes",
the feature is
enabled. If
left blank
or set
to "No"
or
"no",
the feature
is not
enabled.
Note: This
option
requires
CONFIG_IP_NF_TARGET_TCPMSS
<a
href="kernel.htm">in
your kernel</a>.</li>
<li><b>ROUTE_FILTER</b><br>
If this parameter is given the value
"Yes" or "yes" then route filtering (anti-spoofing) is
enabled on all network interfaces. The default value is "no".</li>
</ul>
<h2><a name="modules"></a>
/etc/shorewall/modules Configuration</h2>
<p>The file /etc/shorewall/modules contains commands for loading the kernel
modules required by Shorewall-defined firewall rules.
Shorewall will source this file during start/restart provided
that it exists and that the directory specified by the MODULESDIR
parameter exists (see <a href="#Conf">/etc/shorewall/shorewall.conf</a>
above).</p>
<p>The file that is released with Shorewall calls the Shorewall function
"loadmodule" for the set of modules that I load.</p>
<p>The <i>loadmodule</i> function is called as follows:</p>
<blockquote>
<p>loadmodule
<i>&lt;modulename&gt;
</i>[ <i> &lt;module parameters&gt; </i>]</p>
</blockquote>
<p>where</p>
<blockquote>
<p><i>&lt;modulename&gt; </i></p>
<blockquote>
<p>is the name of the modules without the trailing ".o" (example
ip_conntrack).</p>
</blockquote>
<p><i> &lt;module parameters&gt;</i></p>
<blockquote>
<p> Optional parameters to the insmod utility.</p>
</blockquote>
</blockquote>
<p> The function determines if the module named by <i>&lt;modulename&gt;
</i> is already loaded and if not then the function determines
if the ".o" file corresponding to the module exists in the
<i>moduledirectory</i>; if so, then the following command
is executed:</p>
<blockquote>
<p> insmod <i>moduledirectory</i>/<i>&lt;modulename&gt;</i>.o <i>&lt;module
parameters&gt;</i></p>
</blockquote>
<p> If the file doesn't exist, the function determines of the ".o.gz"
file corresponding to the module exists in the <i>moduledirectory</i>.
If it does, the function assumes that the running configuration supports
compressed modules and execute the following command:</p>
<blockquote>
<p> insmod <i>moduledirectory/&lt;modulename&gt;.</i>o.gz &lt;<i>module
parameters&gt;</i></p>
</blockquote>
<h2><a name="TOS"></a>
/etc/shorewall/tos Configuration</h2>
<p> The /etc/shorewall/tos file allows you to set the Type of Service field
in packet headers based on packet source, packet destination,
protocol, source port and destination port. In order for
this file to be processed by Shorewall, you must have <a
href="#MangleEnabled">mangle support enabled</a> .</p>
<p> Entries in the file have the following columns:</p>
<ul>
<li><b> SOURCE</b> -- The source zone.
May be qualified by following the zone name with a colon
(":") and either an IP address, an IP subnet, a MAC address
in <a href="#MAC">Shorewall Format</a> or the name of an
interface. This column may also contain the <a href="#FW">name of
the firewall</a>
zone
to indicate packets originating on the firewall itself or "all"
to indicate any source.</li>
<li><b> DEST</b> -- The destination
zone. May be qualified by following the zone name with
a colon (":") and either an IP address or an IP subnet.
Because packets are marked prior to routing, you may not specify
the name of an interface. This column may also contain
"all" to indicate any destination.</li>
<li><b> PROTOCOL</b> -- The name of
a protocol in /etc/protocols or the protocol's number.</li>
<li><b> SOURCE PORT(S)</b> -- The source
port or a port range. For all ports, place a hyphen
("-") in this column.</li>
<li><b> DEST PORT(S)</b> -- The destination
port or a port range. To indicate all ports, place a
hyphen ("-") in this column.</li>
<li><b> TOS</b> -- The type of service.
Must be one of the following:</li>
</ul>
<blockquote>
<blockquote>
<p> Minimize-Delay (16)<br>
Maximize-Throughput (8)<br>
Maximize-Reliability (4)<br>
Minimize-Cost (2)<br>
Normal-Service (0)</p>
</blockquote>
</blockquote>
<p> The /etc/shorewall/tos file that is included with Shorewall contains
the following entries.</p>
<blockquote>
<table border="2" cellpadding="2" style="border-collapse: collapse;">
<tbody>
<tr>
<td><b>SOURCE</b></td>
<td><b>DEST</b></td>
<td><b>PROTOCOL</b></td>
<td><b>SOURCE<br>
PORT(S)</b></td>
<td><b>DEST PORT(S)</b></td>
<td><b>TOS</b></td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>-</td>
<td>ssh</td>
<td>16</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>ssh</td>
<td>-</td>
<td>16</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>-</td>
<td>ftp</td>
<td>16</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>ftp</td>
<td>-</td>
<td>16</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>-</td>
<td>ftp-data</td>
<td>8</td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>tcp</td>
<td>ftp-data</td>
<td>-</td>
<td>8</td>
</tr>
</tbody>
</table>
</blockquote>
<p><b>WARNING: </b>Users have reported that odd routing problems result from
adding the ESP and AH protocols to the /etc/shorewall/tos
file. </p>
<h2><a name="Blacklist"></a>/etc/shorewall/blacklist</h2>
<p>Each
line
in
/etc/shorewall/blacklist
contains
an
IP
address, a MAC address in <a
href="#MAC">Shorewall Format</a>
or
subnet
address.
Example:</p>
<pre> 130.252.100.69<br> 206.124.146.0/24</pre>
<p>Packets
<u><b>from</b></u>
hosts
listed
in
the
blacklist
file
will
be
disposed
of
according
to
the
value
assigned
to
the <a href="#Conf">BLACKLIST_DISPOSITION</a>
and <a href="#Conf">BLACKLIST_LOGLEVEL </a>variables
in
/etc/shorewall/shorewall.conf.
Only
packets
arriving
on
interfaces
that
have
the
'<a href="#Interfaces">blacklist</a>'
option
in
/etc/shorewall/interfaces
are
checked
against
the
blacklist. The black list is designed to
prevent listed hosts/subnets from accessing services on <u><b>your</b></u>
network.<br>
</p>
<p>Beginning with Shorewall 1.3.8, the blacklist file has three columns:<br>
</p>
<ul>
<li><b>ADDRESS/SUBNET - </b>As described
above.</li>
<li><b>PROTOCOL</b> - Optional. If specified,
only packets specifying this protocol will be blocked.</li>
<li><b>PORTS - </b>Optional; may only be
given if PROTOCOL is tcp, udp or icmp. Expressed as a comma-separated
list of port numbers or service names (from /etc/services). If
present, only packets destined for the specified protocol and one
of the listed ports are blocked. When the PROTOCOL is icmp, the PORTS
column contains a comma-separated list of ICMP type numbers or names
(see "iptables -h icmp").<br>
</li>
</ul>
<p>Shorewall also has a <a href="blacklisting_support.htm">dynamic blacklist
capability.</a></p>
<p><font color="#cc6666"><b>IMPORTANT: The Shorewall blacklist file is <u>NOT</u>
designed to police your users' web browsing -- to do that,
I suggest that you install and configure Squid (<a
href="http://www.squid-cache.org">http://www.squid-cache.org</a>). </b></font></p>
<h2><a name="rfc1918"></a>/etc/shorewall/rfc1918 (Added in Version 1.3.1)</h2>
<p>This file lists the subnets affected by the <a href="#Interfaces"><i>norfc1918</i>
interface option</a>. Columns in the file are:</p>
<ul>
<li><b>SUBNET</b> - The subnet
using VLSM notation (e.g., 192.168.0.0/16).</li>
<li><b>TARGET<i> </i></b>- What
to do with packets to/from the SUBNET:
<ul>
<li><b>RETURN</b> - Process the
packet normally thru the rules and policies.</li>
<li><b>DROP</b> - Silently drop
the packet.</li>
<li><b>logdrop</b> - Log then
drop the packet -- see the <a href="#Conf">RFC1918_LOG_LEVEL</a>
parameter above.</li>
</ul>
</li>
</ul>
<h2><a name="Routestopped"></a>/etc/shorewall/routestopped (Added in Version
1.3.4)</h2>
<p>This file defines the hosts that are accessible from the firewall when
the firewall is stopped. Columns in the file are:</p>
<ul>
<li><b>INTERFACE </b>- The firewall
interface through which the host(s) comminicate with the firewall.</li>
<li><b>HOST(S) </b>- (Optional)
- A comma-separated list of IP/Subnet addresses. If not supplied
or supplied as "-" then 0.0.0.0/0 is assumed.</li>
</ul>
<p>Example: When your firewall is stopped, you want firewall accessibility
from local hosts 192.168.1.0/24 and from your DMZ. Your DMZ
interfaces through eth1 and your local hosts through eth2.</p>
<blockquote>
<table border="2" style="border-collapse: collapse;" id="AutoNumber1"
cellpadding="2">
<tbody>
<tr>
<td><u><b>INTERFACE</b></u></td>
<td><u><b>HOST(S)</b></u></td>
</tr>
<tr>
<td>eth2</td>
<td>192.168.1.0/24</td>
</tr>
<tr>
<td>eth1</td>
<td>-</td>
</tr>
</tbody>
</table>
</blockquote>
<h2><a name="Maclist"></a>/etc/shorewall/maclist (Added in Version 1.3.10)</h2>
This file is described in the <a
href="MAC_Validation.html">MAC Validation Documentation</a>.<br>
<h2><a name="ECN"></a>/etc/shorewall/ecn (Added in Version 1.4.0)</h2>
This file is described in the <a
href="ECN.html">ECN Control Documentation</a>.<br>
<br>
<p><font size="-1"> Updated 3/21/2003 - <a href="support.htm">Tom Eastep</a>
</font></p>
<p><a href="copyright.htm"><font size="2">Copyright</font> <20> <font
size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
</p>
<br>
<br>
</body>
</html>
View Git Blame Copy Permalink