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<h1 align="center"><font color="#ffffff">Shorewall 1.3 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> 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.</li>
<li><a href="#Scripts"><b> icmp.def</b> </a>--
a parameter file installed in /etc/shorewall and that specifies
the default handling of ICMP packets when the applicable policy
is DROP or REJECT.</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>you must have iproute installed</li>
<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> noping</b> - <b>This option is deprecated and is not available
when OLD_PING_HANDLING=No in /etc/shorewall/shorewall.conf.</b> ICMP echo-request
(ping) packets addressed to the firewall will be ignored by this
interface. <br>
<br>
<b>filterping </b>- <b>This option is deprecated and
is not available when OLD_PING_HANDLING=No in /etc/shorewall/shorewall.conf.</b>
ICMP echo-request (ping) packets addressed to the firewall will
be handled according to the /etc/shorewall/rules and /etc/shorewall/policy
file. If the applicable policy is DROP or REJECT and you have supplied
your own /etc/shorewall/icmpdef file then these 'ping' requests
will be passed through the rules in that file before being dropped or
rejected. If neither <b>noping </b>nor <b>filterping</b>
is specified then the firewall will automatically ACCEPT these
'ping' requests. If both <b>noping</b> and <b>filterping
</b>are specified, <b>filterping</b> takes precedence.</p>
<p> <b> routestopped</b> - Beginning with Shorewall 1.3.4, this option
is deprecated in favor of the <a href="#Routestopped">/etc/shorewall/routestopped</a>
file. When the firewall is stopped, traffic to and from this
interface will be accepted and routing will occur between this
interface and other <i>routestopped </i>interfaces.</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> multi</b> - The interface has multiple addresses and
you want to be able to route between them. Example: you
have two addresses on your single local interface eth1, one
each in subnets 192.168.1.0/24 and 192.168.2.0/24 and you want to
route between these subnets. Because you only have one interface
in the local zone, Shorewall won't normally create a rule to forward
packets from eth1 to eth1. Adding "multi" to the entry for eth1
will cause Shorewall to create the loc2loc chain and the appropriate
forwarding rule.</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>Internal Interface -- <b>routestopped</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>,<b>multi</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>90% of
Shorewall users don't need to put entries in this file and
80% of those who try to add such entries do it wrong.
Unless you are ABSOLUTELY SURE that you need entries in
this file, don't touch it.</b></p>
<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
options.</li>
</ul>
<blockquote>
<p><b>routestopped</b> - Beginning with Shorewall
1.3.4, this option is deprecated in favor of the
<a href="#Routestopped">/etc/shorewall/routestopped</a>
file. When the firewall is stopped, traffic to and from
this host (these hosts) will be accepted and routing will
occur between this host and other <i>routestopped </i>interfaces
and hosts.<br>
<br>
<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 1: </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><font color="#ff0000" size="4"><b>Note 2: </b>
</font> The setting of the MERGE_HOSTS variable
in <a href="#Conf">/etc/shorewall/shorewall.conf</a>
has an important effect on how the host
file is processed. Please read the description
of that variable carefully.</p>
<p>Example:</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>192.168.1.128/25</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>-</td>
<td>eth1</td>
<td>detect</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>routestopped</td>
</tr>
</tbody>
</table>
</blockquote>
<p> Hosts in 'loc2' can communicate with the firewall while Shorewall is
stopped -- those in 'loc1' cannot.</p>
<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>
</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><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>routestopped</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>routestopped</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 or REJECT. 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>
</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.<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 any 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.<br>
</li>
</ul>
</li>
<li><b> PROTO</b> - Protocol. Must be a protocol
name from /etc/protocols, a number, "all" or "related". Specifies
the protocol of the connection request. "related" should be
specified only if you have given ALLOWRELATED="no" in /etc/shorewall/shorewall.conf
and you wish to override that setting for related connections
originating with the client(s) and server(s) specified in
this rule. When "related" is given for the protocol, the remainder
of the columns should be left blank.</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.</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.<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>
<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>To learn how I use Proxy ARP in my DMZ, see <a href="myfiles.htm">my
configuration files</a>.</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.</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.
<b> Note:</b> If two or more NATed systems are connected
to the same firewall interface and you want them to be able to
communicate using their EXTERNAL IP addresses, then you will want
to specify the <b>multi</b> option in the <a
href="#Interfaces">/etc/shorewall/interface</a> entry for that interface.</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
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>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>OLD_PING_HANDLING - </b>Added at version 1.3.14.<br>
If this option is set to 'Yes' then the old and confusing ICMP echo-request
(Ping) handling is enabled. This includes the 'noping' and 'filterping' interface
options and the FORWARDPING option below. If this option is set to "No" then
ping requests are handled using rules and policies just like any other connection
request. For upward compatibility with only configurations, if this option
is omitted OLD_PING_HANDLING=Yes is assumed. New Shorewall users should leave
this option set to "No".<br>
<br>
For a complete description of how ping handling works under Shorewall, see
<a href="ping.html">ping.html</a>.<br>
<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>FORWARDPING</b> - Added in Version 1.3.7 - <b>This
option is deprecated and is not available when OLD_PING_HANDLING=No (see
above).</b><br>
When set to "Yes" or "yes", ICMP echo-request (ping)
packets from interfaces that specify "filterping" are ACCEPTed
by the firewall. When set to "No" or "no", such ping requests
are silently dropped unless they are handled by an explicit entry
in the <a href="#Rules">rules file</a>. If not specified, "No" is
assumed.<2E></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.<br>
</li>
<li><b>MERGE_HOSTS </b>- Added in Version 1.3.5<br>
Prior to 1.3.5, when the <a href="#Hosts">/etc/shorewall/hosts</a>
file included an entry for a zone then the entire zone had
to be defined in the /etc/shorewall/hosts file and any associations
between the zone and interfaces in the <a href="#Interfaces">/etc/shorewall/interfaces</a>
file were ignored. This behavior is preserved if MERGE_HOSTS=No
or if MERGE_HOSTS is not set or is set to the empty value.<br>
<br>
Beginning with version 1.3.5, if MERGE_HOSTS=Yes,
then zone assignments in the /etc/shorewall/hosts file are ADDED
to those in the /etc/shorewall/interfaces file. <br>
<br>
Example:<br>
<br>
Interfaces File:<br>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber2">
<tbody>
<tr>
<td><u><b>ZONE</b></u></td>
<td><u><b>HOSTS</b></u></td>
<td><u><b>BROADCAST</b></u></td>
<td><u><b>OPTIONS</b></u></td>
</tr>
<tr>
<td>loc</td>
<td>eth1</td>
<td>-</td>
<td>dhcp</td>
</tr>
<tr>
<td>-</td>
<td>ppp+</td>
<td> <br>
</td>
<td> <br>
</td>
</tr>
</tbody>
</table>
<p><br>
Hosts File:<br>
</p>
<table border="1" cellpadding="2" style="border-collapse: collapse;"
id="AutoNumber3">
<tbody>
<tr>
<td><u><b>ZONE</b></u></td>
<td><u><b>HOSTS</b></u></td>
</tr>
<tr>
<td>loc</td>
<td>ppp+:192.168.12.0/24</td>
</tr>
</tbody>
</table>
<p><font face="Courier"><br>
</font>With MERGE_HOSTS=No, the<b> loc</b> zone consists
of only ppp+:192.168.12.0/24; with MERGE_HOSTS=Yes, it includes
eth1:0.0.0.0/0 and ppp+:192.168.12.0/24.<br>
</p>
</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>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> ALLOWRELATED</b><br>
This parameter must be assigned the value "Yes"
("yes") or "No" ("no") and specifies whether Shorewall
allows connection requests that are related to an already allowed
connection. If you say "No" ("no"), you can still override this
setting by including "related" rules in /etc/shorewall/rules ("related"
given as the protocol). If you specify ALLOWRELATED=No, you will
need to include rules in <a
href="shorewall_extension_scripts.htm">/etc/shorewall/icmpdef</a> to
handle common ICMP packet types.</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>
<br>
<p><font size="-1"> Updated 1/21/2003 - <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>
<br>
</p>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
</body>
</html>
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