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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><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+). <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).<2E></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. 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> - 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>.<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.<br>
</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 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<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="#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 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><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>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, $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:<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>
<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>
PORTS(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.</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, 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.<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> <b><a href="IPIP.htm">instructions for IPIP and
GRE tunnels are here</a> <20></b>and <b><a href="PPTP.htm">instructions
for PPTP tunnels are here</a>.</b></p>
<h2>/etc/shorewall/shorewall.conf</h2>
<p> This file is used to set the following firewall parameters:</p>
<ul>
<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 syslogd log level 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 syslogd log level 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<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<EFBFBD> "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>/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.<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>
<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="2"> Updated 11/24/2002 - <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>
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