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teastep f556717fc5 Shorewall 1.4.5 
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<h1 align="center"><font color="#ffffff">Shorewall 1.4 Reference</font></h1>
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<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 (4 characters or less if you are running Shorewall 1.4.4
or later) 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:<br>
<br>
<b>newnotsyn </b>(Added in version 1.4.6) - This option overrides
<a href="#Conf">NEWNOTSYN=No</a> for packets arriving on this interface.
<br>
<b><br>
routeback </b>(Added in version 1.4.2) - This option causes Shorewall
to set up handling for routing packets that arrive on this interface back
out the same interface. If this option is specified, the ZONE column
may not contain "-".<br>
<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>routeback </b>(Added in version 1.4.2) - This option causes Shorewall
to set up handling for routing packets sent by this host group back
back to the same group.<b><br>
<br>
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>REDIRECT- -- The above ACTION (REDIRECT) generates two
iptables rules: 1) and header-rewriting rule in the Netfilter
'nat' table and; 2) an ACCEPT rule in the Netfilter 'filter' table.
REDIRECT- works like REDIRECT but only generates the header-rewriting
rule.<br>
</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="configuration_file_basics.htm#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 particular IP addresses (see Example 2 below
for another usage). Those IP addresses are specified in the ORIGINAL
DEST column as a comma-separated list.<br>
<br>
The IP address(es) 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>
If this list begins with "!" then the rule will only apply if the original
destination address matches none of the addresses listed.<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. </b>Your firewall's external
interface has several IP addresses but you only want to accept SSH connections
on address 206.124.146.176.<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">net<br>
</td>
<td valign="top">fw:206.124.146.176<br>
</td>
<td valign="top">tcp<br>
</td>
<td valign="top">22<br>
</td>
<td valign="top"><br>
</td>
<td valign="top"><br>
</td>
</tr>
</tbody>
</table>
</blockquote>
<b>Example 8 (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>, PPTP
and 6to4.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>,
<b><a href="PPTP.htm">instructions for PPTP tunnels are here</a>
and <a href="6to4.htm">instructions for 6to4 tunnels</a> are here.</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>LOGFORMAT
- </b>Added at version 1.4.4.<br>
The value of this variable generate the --log-prefix setting for Shorewall
logging rules. It contains a 'printf' formatting template which accepts
three arguments (the chain name, logging rule number (optional) and the
disposition). To use LOGFORMAT with fireparse (<a
href="http://www.fireparse.com">http://www.fireparse.com</a>), set it
as:<br>
<20><br>
<20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD> LOGFORMAT="fp=%s:%d a=%s "<br>
<20><br>
If the LOGFORMAT value contains the substring '%d' then the logging rule
number is calculated and formatted in that position; if that substring
is not included then the rule number is not included. If not supplied or
supplied as empty (LOGFORMAT="") then "Shorewall:%s:%s:" is assumed.<br>
<br>
<b>CAUTION: </b>/sbin/shorewall uses the leading part of the LOGFORMAT
string (up to but not including the first '%') to find log messages in
the 'show log', 'status' and 'hits' commands. This part should not be
omitted (the LOGFORMAT should not begin with "%") and the leading part
should be sufficiently unique for /sbin/shorewall to identify Shorewall
messages.<br>
</li>
<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
first IP address of the interface to the source zone and will include
this address in DNAT rules as the original destination IP address.
If set to "No" or "no", Shorewall will not detect this address
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. <b>RESTRICTION: </b>Shorewall can only add addresses
to the first subnetwork configured on an interface.<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. <b>RESTRICTION: </b>Shorewall
can only add addresses to the first subnetwork configured on an interface.<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 <a
href="configuration_file_basics.htm#MAC">in </a><a
href="configuration_file_basics.htm#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="configuration_file_basics.htm#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>
<p><font size="-1"> Updated 6/2/2003 - <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>
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