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Index: en_US.ISO8859-1/books/handbook/firewalls/chapter.xml
===================================================================
--- en_US.ISO8859-1/books/handbook/firewalls/chapter.xml
+++ en_US.ISO8859-1/books/handbook/firewalls/chapter.xml
@@ -1698,7 +1698,7 @@
<warning>
<para>Only firewall rules with the <option>log</option> option will
be logged. The default rules do not include this option and it
- must be manually added. Therefor it is advisable that the default
+ must be manually added. Therefore it is advisable that the default
ruleset is edited for logging. In addition, log rotation may be
desired if the logs are stored in a separate file.</para>
</warning>
@@ -2121,9 +2121,9 @@
&dollar;cmd 00999 deny log all from any to any</programlisting>
</sect2>
- <sect2 xml:id="network-natd">
+ <sect2 xml:id="in-kernel-nat">
<info>
- <title>Configuring <acronym>NAT</acronym></title>
+ <title>In-kernel <acronym>NAT</acronym></title>
<authorgroup>
<author>
@@ -2134,7 +2134,18 @@
<contrib>Contributed by </contrib>
</author>
</authorgroup>
+
+ <authorgroup>
+ <author>
+ <personname>
+ <firstname>Dries</firstname>
+ <surname>Michiels</surname>
+ </personname>
+ <contrib>Rewritten and updated by </contrib>
+ </author>
+ </authorgroup>
</info>
+
<indexterm>
<primary>NAT</primary>
@@ -2141,12 +2152,16 @@
<secondary>and <application>IPFW</application></secondary>
</indexterm>
- <para>&os;'s built-in <acronym>NAT</acronym> daemon,
- &man.natd.8;, works in conjunction with
+ <para>&os;'s <application>IPFW</application> firewall has two
+ implementations of <acronym>NAT</acronym>: one being the
+ userland &man.natd.8; daemon, and the more recent
+ <application>IPFW</application>'s built-in
+ <acronym>NAT</acronym> facility also known as in-kernel
+ <acronym>NAT</acronym>. Both work in conjunction with
<application>IPFW</application> to provide network address
translation. This can be used to provide an Internet
Connection Sharing solution so that several internal computers
- can connect to the Internet using a single
+ can connect to the Internet using a single public
<acronym>IP</acronym> address.</para>
<para>To do this, the &os; machine connected to the Internet
@@ -2157,58 +2172,80 @@
<acronym>LAN</acronym> should be assigned an
<acronym>IP</acronym> address in the private network space, as
defined by <link
- xlink:href="https://www.ietf.org/rfc/rfc1918.txt">RFC
- 1918</link>, and have the default gateway set to the
- &man.natd.8; system's internal <acronym>IP</acronym>
- address.</para>
+ xlink:href="https://www.ietf.org/rfc/rfc1918.txt">RFC
+ 1918</link>.</para>
- <para>Some additional configuration is needed in order to
- activate the <acronym>NAT</acronym> function of
- <application>IPFW</application>. If the system has a custom
- kernel, the kernel configuration file needs to include
- <literal>option IPDIVERT</literal> along with the other
- <literal>IPFIREWALL</literal> options described in <xref
- linkend="firewalls-ipfw-enable"/>.</para>
+ <para>Some additional configuration is needed in order to enable
+ the in-kernel <acronym>NAT</acronym> function of
+ <application>IPFW</application>. To enable in-kernel
+ <acronym>NAT</acronym> support at boot time, the following
+ must be set in <filename>/etc/rc.conf</filename>:</para>
- <para>To enable <acronym>NAT</acronym> support at boot time, the
- following must be in <filename>/etc/rc.conf</filename>:</para>
+ <programlisting>gateway_enable="YES"
+firewall_enable="YES"
+firewall_nat_enable="YES"</programlisting>
- <programlisting>gateway_enable="YES" # enables the gateway
-natd_enable="YES" # enables <acronym>NAT</acronym>
-natd_interface="rl0" # specify interface name of NIC attached to Internet
-natd_flags="-dynamic -m" # -m = preserve port numbers; additional options are listed in &man.natd.8;</programlisting>
-
<note>
- <para>It is also possible to specify a configuration file
- which contains the options to pass to &man.natd.8;:</para>
+ <para>When <literal>firewall_enable</literal> is not set,
+ but <literal>firewall_nat_enable</literal> is, it will have
+ no effect and do nothing. This is by design with the
+ following reason: <application>IPFW</application>'s
+ in-kernel <acronym>NAT</acronym> facility is specific to
+ <application>IPFW</application>. In order to use
+ <application>IPFW</application>'s <acronym>NAT</acronym>,
+ <application>IPFW</application> should also be enabled and
+ loaded by setting
+ <literal>firewall_enable</literal>.</para></note>
- <programlisting>natd_flags="-f /etc/natd.conf"</programlisting>
+ <para>When the ruleset contains stateful rules, the positioning
+ of the <acronym>NAT</acronym> rule is critical and the
+ <literal>skipto</literal> action is used. The
+ <literal>skipto</literal> action requires a rule number so
+ that it knows which rule to jump to. Furthermore, because of
+ the nature of a stateful <acronym>NAT</acronym>ing firewall,
+ it is necessary to allow translated packets to be reinjected
+ in the firewall for further processing. Because of the
+ architecture of &man.libalias.3;, a library implemented as a
+ kernel module used for the in-kernel <acronym>NAT</acronym>
+ facility of <application>IPFW</application>, it is necessary
+ to disable TCP segmentation offloading, or in short
+ <acronym>TSO</acronym>. <acronym>TSO</acronym> can be
+ disabled on a per network interface basis using
+ &man.ifconfig.8; or on a system wide basis using
+ &man.sysctl.8;. To allow packets to be reinjected and to
+ disable <acronym>TSO</acronym> system wide, the following must
+ be set in <filename>/etc/sysctl.conf</filename>:</para>
- <para>The specified file must contain a list of configuration
- options, one per line. For example:</para>
+ <programlisting>net.inet.ip.fw.one_pass="0"
+net.inet.tcp.tso="0"</programlisting>
- <programlisting>redirect_port tcp 192.168.0.2:6667 6667
-redirect_port tcp 192.168.0.3:80 80</programlisting>
-
- <para>For more information about this configuration file,
- consult &man.natd.8;.</para>
- </note>
-
- <para>Next, add the <acronym>NAT</acronym> rules to the firewall
- ruleset. When the rulest contains stateful rules, the
- positioning of the <acronym>NAT</acronym> rules is critical
- and the <literal>skipto</literal> action is used. The
- <literal>skipto</literal> action requires a rule number so
- that it knows which rule to jump to.</para>
-
<para>The following example builds upon the firewall ruleset
shown in the previous section. It adds some additional
entries and modifies some existing rules in order to configure
- the firewall for <acronym>NAT</acronym>. It starts by adding
- some additional variables which represent the rule number to
- skip to, the <literal>keep-state</literal> option, and a list
- of <acronym>TCP</acronym> ports which will be used to reduce
- the number of rules:</para>
+ the firewall for in-kernel <acronym>NAT</acronym>. It starts
+ by adding some additional variables which represent the rule
+ number to skip to, the <literal>keep-state</literal> option,
+ and a list of <acronym>TCP</acronym> ports which will be used
+ to reduce the number of rules. A <acronym>NAT</acronym>
+ instance will also be configured. With in-kernel
+ <acronym>NAT</acronym> it is possible to have multiple
+ <acronym>NAT</acronym> instances each with their own
+ configuration. Although, for this example only one
+ <acronym>NAT</acronym> instance is needed;
+ <acronym>NAT</acronym> instance number 1. The configuration
+ takes a few arguments and flags such as: <option>if</option>
+ which indicates the public interface,
+ <option>same_ports</option> which takes care that alliased
+ ports and local port numbers are mapped the same,
+ <option>unreg_only</option> will result in only unregistered
+ (private) address spaces to be processed by the
+ <acronym>NAT</acronym> instance, and <option>reset</option>
+ which will help to keep a functioning <acronym>NAT</acronym>
+ instance even when the public <acronym>IP</acronym> address of
+ the <application>IPFW</application> machine changes. For all
+ possible options that can be passed to a single
+ <acronym>NAT</acronym> configuration consult
+ &man.ipfw.8;.</para>
<programlisting>#!/bin/sh
ipfw -q -f flush
@@ -2216,7 +2253,9 @@
skip="skipto 500"
pif=dc0
ks="keep-state"
-good_tcpo="22,25,37,53,80,443,110"</programlisting>
+good_tcpo="22,25,37,53,80,443,110"
+# Configure the in-kernel NAT instance
+ipfw -q nat 1 config if &dollar;pif same_ports unreg_only reset</programlisting>
<para>The inbound <acronym>NAT</acronym> rule is inserted
<emphasis>after</emphasis> the two rules which allow all
@@ -2230,7 +2269,7 @@
<programlisting>&dollar;cmd 005 allow all from any to any via xl0 # exclude LAN traffic
&dollar;cmd 010 allow all from any to any via lo0 # exclude loopback traffic
-&dollar;cmd 100 divert natd ip from any to any in via &dollar;pif # NAT any inbound packets
+&dollar;cmd 100 nat 1 ip from any to any in via &dollar;pif # NAT any inbound packets
# Allow the packet through if it has an existing entry in the dynamic rules table
&dollar;cmd 101 check-state</programlisting>
@@ -2263,7 +2302,7 @@
to pass.</para>
<programlisting>&dollar;cmd 499 deny log all from any to any
-&dollar;cmd 500 divert natd ip from any to any out via &dollar;pif # skipto location for outbound stateful rules
+&dollar;cmd 500 nat 1 ip from any to any out via &dollar;pif # skipto location for outbound stateful rules
&dollar;cmd 510 allow ip from any to any</programlisting>
<para>In this example, rules <literal>100</literal>,
@@ -2312,15 +2351,15 @@
<sect3>
<title>Port Redirection</title>
- <para>The drawback with &man.natd.8; is that the
- <acronym>LAN</acronym> clients are not accessible from the
- Internet. Clients on the <acronym>LAN</acronym> can make
- outgoing connections to the world but cannot receive
- incoming ones. This presents a problem if trying to run
- Internet services on one of the <acronym>LAN</acronym>
+ <para>The drawback with <acronym>NAT</acronym> in general is
+ that the <acronym>LAN</acronym> clients are not accessible
+ from the Internet. Clients on the <acronym>LAN</acronym>
+ can make outgoing connections to the world but cannot
+ receive incoming ones. This presents a problem if trying to
+ run Internet services on one of the <acronym>LAN</acronym>
client machines. A simple way around this is to redirect
- selected Internet ports on the &man.natd.8; machine to a
- <acronym>LAN</acronym> client.</para>
+ selected Internet ports on the <acronym>NAT</acronym>
+ providing machine to a <acronym>LAN</acronym> client.</para>
<para>For example, an <acronym>IRC</acronym> server runs on
client <systemitem>A</systemitem> and a web server runs on
@@ -2329,49 +2368,50 @@
(<acronym>IRC</acronym>) and 80 (<acronym>HTTP</acronym>)
must be redirected to the respective machines.</para>
- <para>The syntax for <option>-redirect_port</option> is as
- follows:</para>
+ <para>With in-kernel <acronym>NAT</acronym> all configuration
+ is done in the <acronym>NAT</acronym> instance configuration.
+ For a full list of options that an in-kernel
+ <acronym>NAT</acronym> instance can use, consult &man.ipfw.8;.
+ The <application>IPFW</application> syntax follows the syntax
+ of <application>natd</application>. The syntax for
+ <option>redirect_port</option> is as follows:</para>
- <programlisting> -redirect_port proto targetIP:targetPORT[-targetPORT]
- [aliasIP:]aliasPORT[-aliasPORT]
- [remoteIP[:remotePORT[-remotePORT]]]</programlisting>
+ <programlisting>redirect_port proto targetIP:targetPORT[-targetPORT]
+ [aliasIP:]aliasPORT[-aliasPORT]
+ [remoteIP[:remotePORT[-remotePORT]]]</programlisting>
- <para>In the above example, the argument should be:</para>
+ <para>To configure the above example setup, the arguments
+ should be:</para>
- <programlisting> -redirect_port tcp 192.168.0.2:6667 6667
- -redirect_port tcp 192.168.0.3:80 80</programlisting>
+ <programlisting>redirect_port tcp 192.168.0.2:6667 6667
+redirect_port tcp 192.168.0.3:80 80</programlisting>
- <para>This redirects the proper <acronym>TCP</acronym> ports
- to the <acronym>LAN</acronym> client machines.</para>
+ <para>After adding these arguments to configuration of
+ <acronym>NAT</acronym> instance 1 in the above ruleset, the
+ <acronym>TCP</acronym> ports will be port forwarded to the
+ <acronym>LAN</acronym> client machines running the
+ <acronym>IRC</acronym> and <acronym>HTTP</acronym>
+ services.</para>
+ <programlisting>ipfw -q nat 1 config if &dollar;pif same_ports unreg_only reset \
+ redirect_port tcp 192.168.0.2:6667 6667 \
+ redirect_port tcp 192.1683.0.3:80 80</programlisting>
+
<para>Port ranges over individual ports can be indicated with
- <option>-redirect_port</option>. For example,
+ <option>redirect_port</option>. For example,
<replaceable>tcp 192.168.0.2:2000-3000
- 2000-3000</replaceable> would redirect all connections
+ 2000-3000</replaceable> would redirect all connections
received on ports 2000 to 3000 to ports 2000 to 3000 on
client <systemitem>A</systemitem>.</para>
-
- <para>These options can be used when directly running
- &man.natd.8;, placed within the
- <literal>natd_flags=""</literal> option in
- <filename>/etc/rc.conf</filename>, or passed via a
- configuration file.</para>
-
- <para>For further configuration options, consult
- &man.natd.8;.</para>
</sect3>
<sect3>
<title>Address Redirection</title>
- <indexterm>
- <primary>address redirection</primary>
- </indexterm>
-
<para>Address redirection is useful if more than one
<acronym>IP</acronym> address is available. Each
<acronym>LAN</acronym> client can be assigned its own
- external <acronym>IP</acronym> address by &man.natd.8;,
+ external <acronym>IP</acronym> address by &man.ipfw.8;,
which will then rewrite outgoing packets from the
<acronym>LAN</acronym> clients with the proper external
<acronym>IP</acronym> address and redirects all traffic
@@ -2383,7 +2423,7 @@
class="ipaddress">128.1.1.2</systemitem>, and <systemitem
class="ipaddress">128.1.1.3</systemitem> are available,
<systemitem class="ipaddress">128.1.1.1</systemitem> can be
- used as the &man.natd.8; machine's external
+ used as the &man.ipfw.8; machine's external
<acronym>IP</acronym> address, while <systemitem
class="ipaddress">128.1.1.2</systemitem> and <systemitem
class="ipaddress">128.1.1.3</systemitem> are forwarded
@@ -2391,49 +2431,88 @@
<systemitem>A</systemitem> and
<systemitem>B</systemitem>.</para>
- <para>The <option>-redirect_address</option> syntax is as
- follows:</para>
+ <para>The <option>redirect_address</option> syntax is as
+ below, where <literal>localIP</literal> is the internal
+ <acronym>IP</acronym> address of the <acronym>LAN</acronym>
+ client, and <literal>publicIP</literal> the external
+ <acronym>IP</acronym> address corresponding to the
+ <acronym>LAN</acronym> client.</para>
- <programlisting>-redirect_address localIP publicIP</programlisting>
+<programlisting>redirect_address localIP PublicIP</programlisting>
+ <para>In the example, the arguments would read:</para>
- <informaltable frame="none" pgwide="1">
- <tgroup cols="2">
- <tbody>
- <row>
- <entry>localIP</entry>
- <entry>The internal <acronym>IP</acronym> address of
- the <acronym>LAN</acronym> client.</entry>
- </row>
+ <programlisting>redirect_address 192.168.0.2 128.1.1.2
+redirect_address 192.168.0.3 128.1.1.3</programlisting>
- <row>
- <entry>publicIP</entry>
- <entry>The external <acronym>IP</acronym> address
- corresponding to the <acronym>LAN</acronym>
- client.</entry>
- </row>
- </tbody>
- </tgroup>
- </informaltable>
-
- <para>In the example, this argument would read:</para>
-
- <programlisting>-redirect_address 192.168.0.2 128.1.1.2
--redirect_address 192.168.0.3 128.1.1.3</programlisting>
-
- <para>Like <option>-redirect_port</option>, these arguments
- are placed within the <literal>natd_flags=""</literal>
- option of <filename>/etc/rc.conf</filename>, or passed via a
- configuration file. With address redirection, there is no
- need for port redirection since all data received on a
+ <para>Like <option>redirect_port</option>, these arguments
+ are placed in a <acronym>NAT</acronym> instance
+ configuration. With address redirection, there is no
+ need for port redirection, as all data received on a
particular <acronym>IP</acronym> address is
redirected.</para>
<para>The external <acronym>IP</acronym> addresses on the
- &man.natd.8; machine must be active and aliased to the
+ &man.ipfw.8; machine must be active and aliased to the
external interface. Refer to &man.rc.conf.5; for
details.</para>
</sect3>
+
+ <sect3>
+ <title>Userspace <acronym>NAT</acronym></title>
+
+ <para>Lets start with a statement: the userspace
+ <acronym>NAT</acronym> implementation: &man.natd.8;, has
+ more overhead than in-kernel <acronym>NAT</acronym>. This
+ is due to the fact that in order for &man.natd.8; to
+ translate packets, the packets have to be copied from the
+ kernel to userspace which brings in the overhead.</para>
+
+ <para>To enable the userpace <acronym>NAT</acronym> daemon;
+ &man.natd.8; at boot time, the following is a minimum
+ configuration in <filename>/etc/rc.conf</filename>. Where
+ <option>natd_interface</option> is set to the name of the
+ <acronym>NIC</acronym> attached to the Internet. The
+ &man.rc.8; script of &man.natd.8; will automatically check
+ if a dynamic <acronym>IP</acronym> address is used and
+ configure itself to handle that.</para>
+
+ <programlisting>gateway_enable="YES"
+natd_enable="YES"
+natd_interface="rl0"</programlisting>
+
+ <para>In general, the above ruleset as explained for in-kernel
+ <acronym>NAT</acronym> can also used together with
+ &man.natd.8;. The only exceptions are the configuration of
+ the in-kernel <acronym>NAT</acronym> instance <literal>(ipfw
+ -q nat 1 config ...)</literal> not being applicable any
+ more, and rule number 100 and 500 will have to change
+ sligthly as below.</para>
+
+ <programlisting>&dollar;cmd 100 divert natd ip from any to any in via &dollar;pif
+&dollar;cmd 500 divert natd ip from any to any out via &dollar;pif</programlisting>
+
+ <para>To configure port or address redirection, a similar
+ syntax as with in-kernel <acronym>NAT</acronym> is used.
+ Although, now, instead of specifying the configuration in
+ our ruleset script like with in-kernel
+ <acronym>NAT</acronym>, configuration of &man.natd.8; is
+ best done in a configuration file. To do this, an extra
+ flag must be passed via <filename>/etc/rc.conf</filename>
+ which specifies the path of the configuration file.</para>
+
+ <programlisting>natd_flags="-f /etc/natd.conf"</programlisting>
+
+ <note>
+ <para>The specified file must contain a list of
+ configuration options, one per line. For more information
+ about the configuration file and possible variables,
+ consult &man.natd.8;. Below are two example
+ entries, one per line:</para>
+
+ <programlisting>redirect_port tcp 192.168.0.2:6667 6667
+redirect_address 192.168.0.3 128.1.1.3</programlisting></note>
+ </sect3>
</sect2>
<sect2 xml:id="firewalls-ipfw-cmd">

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