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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="#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><EFBFBD>
/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<6F> 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=noping,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 noping,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<6F> "-". 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+)</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).<2E></li>
</ul>
</li>
<li><b> OPTIONS</b> - a comma-separated list of options. Possible
options include:
<p> <b>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> - ICMP echo-request (ping) packets addressed to
the firewall will be ignored by this interface.<br>
<br>
<b>filterping </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><b><font color="#ff6633">Update 12/20/2001: </font></b>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>.</p>
</li>
</ul>
<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 ignore ping requests from the
internet and 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,noping,norfc1918,blacklist</td>
</tr>
<tr>
<td>loc</td>
<td>eth1</td>
<td>detect</td>
<td><EFBFBD></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><EFBFBD></td>
<td><EFBFBD></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><EFBFBD></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 the form <i>&lt;subnet address&gt;/&lt;width&gt;
</i>(example - eth2:192.168.2.0/2)</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. Currently
only a single option is defined:</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.</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<32></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,noping,norfc1918</td>
</tr>
<tr>
<td>-</td>
<td>eth1</td>
<td>detect</td>
<td><EFBFBD></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><EFBFBD></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.<2E></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="#FW">name of the firewall</a> zone 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="#FW">name of the firewall</a> zone or "all").</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 syslog level. See the syslog.conf man page for a description of
each log level.</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.<2E></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><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
<td><EFBFBD></td>
</tr>
<tr>
<td>all</td>
<td>all</td>
<td>REJECT</td>
<td>info</td>
<td><EFBFBD></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><EFBFBD>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><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>net</td>
<td>all</td>
<td>DROP</td>
<td>info</td>
<td><EFBFBD></td>
</tr>
<tr>
<td>loc</td>
<td>loc</td>
<td>REJECT</td>
<td>info</td>
<td><EFBFBD></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,noping,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><EFBFBD></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><EFBFBD> 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><EFBFBD></td>
</tr>
<tr>
<td>sam</td>
<td>all</td>
<td>CONTINUE</td>
<td><EFBFBD></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><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></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><EFBFBD></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><EFBFBD></td>
</tr>
<tr>
<td>...</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></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> <20></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><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>...</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
<tr>
<td>DNAT</td>
<td>sam</td>
<td>fw</td>
<td>tcp</td>
<td>ssh</td>
<td>-</td>
<td><EFBFBD></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><EFBFBD></td>
</tr>
<tr>
<td>...</td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></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.<2E></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>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 syslogd log
level (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>
<20> </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 or $FW. 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>
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).<2E></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>
</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:<3A> </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<41><54><EFBFBD><EFBFBD> loc<u>:192.168.1.0/24</u><EFBFBD><EFBFBD><EFBFBD> loc:192.168.1.3<EFBFBD><EFBFBD><EFBFBD>
tcp<63><70><EFBFBD> www<77><77><EFBFBD> -<2D><><EFBFBD> 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.<2E></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><EFBFBD></td>
<td><EFBFBD></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><EFBFBD></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><EFBFBD></td>
<td><EFBFBD></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><EFBFBD></td>
</tr>
<tr>
<td>ACCEPT</td>
<td>loc</td>
<td>dmz:155.186.235.222</td>
<td>tcp</td>
<td>www</td>
<td><EFBFBD></td>
<td><EFBFBD></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><EFBFBD></td>
<td><EFBFBD></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<74> 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><EFBFBD></td>
<td><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
</blockquote>
<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<6F> (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.</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:<3A><><EFBFBD><EFBFBD></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><EFBFBD></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><EFBFBD></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.<2E></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><EFBFBD><EFBFBD><EFBFBD><EFBFBD> qt service ipsec stop</p>
<p>In /etc/shorewall/start, include:</p>
<p><EFBFBD><EFBFBD><EFBFBD> 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<65> <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 and
IPIP 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.<2E></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>and <b><a href="IPIP.htm">instructions for IPIP
tunnels are here</a> . </b>Look <a href="PPTP.htm">here</a> for information
about setting up PPTP
tunnels under
Shorewall.</p>
<h2><font color="#660066"><a name="Conf"></a>
</font>/etc/shorewall/shorewall.conf</h2>
<p> This file is used to set the following firewall parameters:</p>
<ul>
<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<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.</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 syslog level at which you want
the packets logged. Example: LOGNEWNOTSYN=debug|<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>
<20></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>
<20>
<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><EFBFBD></td>
<td><EFBFBD></td>
</tr>
</tbody>
</table>
<p><br>
Hosts File:<br>
<20></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>
<20> </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>
<20>
<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>
<20><><EFBFBD> LOGRATE=10/minute<br>
<20><><EFBFBD> LOGBURST=5<br>
<20></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.<2E>NAT
operations include:<br>
<br>
<20><><EFBFBD> Static NAT<br>
<20><><EFBFBD> Port Forwarding<br>
<20><><EFBFBD> Port Redirection<br>
<20><><EFBFBD> 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>
<20><><EFBFBD> On or on - packet forwarding will be enabled.<br>
<20><><EFBFBD> Off or off - packet forwarding will be disabled.<br>
<20><><EFBFBD> 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 syslog
log level
(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;<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD></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.<2E>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<69> "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><EFBFBD> -- 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.</li>
</ul>
</li>
</ul>
<h2><a name="Routestopped"></a>25. /etc/shorewall/routestopped (Added in Version
1.3.4)</h2>
<p>This fine defines the hosts that are accessible from the firewall when
the firewall is stopped.<2E> 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>
<p><font size="2"> Updated 9/28/2002 - <a href="support.htm">Tom Eastep</a>
</font></p>
<p><font face="Trebuchet MS"><a href="copyright.htm"><font size="2">Copyright</font>
<20> <font size="2">2001, 2002 Thomas M. Eastep.</font></a></font></p>
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face="Century Gothic, Arial, Helvetica">
</font><br>
<br>
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