forked from extern/shorewall_code
af3aa96964
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@8563 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
441 lines
16 KiB
XML
441 lines
16 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id="IPSEC">
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<!--$Id$-->
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<articleinfo>
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<title>IPSEC Tunnels</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2001-2005</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 3.0 and
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later. If you are running a version of Shorewall earlier than Shorewall
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3.0.0 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<important>
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<para>The information in this article is only applicable if you plan to
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have IPSEC end-points on the same system where Shorewall is used.</para>
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</important>
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<warning>
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<para>This documentation is incomplete regarding using IPSEC and the 2.6
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Kernel. Netfilter currently lacks full support for the 2.6 kernel's
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implementation of IPSEC. Until that implementation is complete, only a
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simple network-network tunnel is described for 2.6.</para>
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<para>UPDATE: Some distributions such as <trademark>SUSE</trademark> are
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now shipping Kernels and iptables with the IPSEC-Netfilter patches and
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policy match support. Check <ulink url="IPSEC-2.6.html">this
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article</ulink> for information concerning this support and
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Shorewall.</para>
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</warning>
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<section id="Prelim">
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<title>Preliminary Reading</title>
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<para>I recommend reading the <ulink url="VPNBasics.html">VPN
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Basics</ulink> article if you plan to implement any type of VPN.</para>
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</section>
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<section id="Swans">
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<title>Configuring FreeS/Wan and Derivatives Such as OpenS/Wan</title>
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<para>There is an excellent guide to configuring IPSEC tunnels at <ulink
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url="http://jixen.tripod.com/">http://jixen.tripod.com/</ulink>. I highly
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recommend that you consult that site for information about configuring
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FreeS/Wan.</para>
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<important>
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<para>The documentation below assumes that you have disabled
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opportunistic encryption feature in FreeS/Wan 2.0 using the following
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additional entries in ipsec.conf:</para>
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<programlisting>conn block
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auto=ignore
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conn private
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auto=ignore
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conn private-or-clear
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auto=ignore
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conn clear-or-private
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auto=ignore
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conn clear
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auto=ignore
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conn packetdefault
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auto=ignore</programlisting>
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<para>For further information see <ulink
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url="http://www.freeswan.org/freeswan_trees/freeswan-2.03/doc/policygroups.html">http://www.freeswan.org/freeswan_trees/freeswan-2.03/doc/policygroups.html</ulink>.</para>
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</important>
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</section>
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<section id="GwFw">
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<title>IPSec Gateway on the Firewall System</title>
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<para>Suppose that we have the following sutuation:</para>
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<graphic fileref="images/TwoNets1.png" />
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<para>We want systems in the 192.168.1.0/24 sub-network to be able to
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communicate with systems in the 10.0.0.0/8 network. We assume that on both
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systems A and B, eth0 is the internet interface.</para>
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<para>To make this work, we need to do two things:</para>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>Open the firewall so that the IPSEC tunnel can be established
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(allow the ESP and AH protocols and UDP Port 500).</para>
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</listitem>
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<listitem>
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<para>Allow traffic through the tunnel.</para>
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</listitem>
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</orderedlist>
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<para>Opening the firewall for the IPSEC tunnel is accomplished by adding
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an entry to the /etc/shorewall/tunnels file.</para>
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<para>In /etc/shorewall/tunnels on system A, we need the following</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 134.28.54.2</programlisting>
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<para>In /etc/shorewall/tunnels on system B, we would have:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 206.161.148.9</programlisting>
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<note>
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<para>If either of the endpoints is behind a NAT gateway then the
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tunnels file entry on the <emphasis role="bold">other</emphasis>
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endpoint should specify a tunnel type of ipsecnat rather than ipsec and
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the GATEWAY address should specify the external address of the NAT
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gateway.</para>
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</note>
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<para>You need to define a zone for the remote subnet or include it in
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your local zone. In this example, we'll assume that you have created a
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zone called <quote>vpn</quote> to represent the remote subnet. Note that
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you should define the vpn zone before the net zone.</para>
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<para>/etc/shorewall/zones (both systems):</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn ipv4
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net ipv4</programlisting>
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<para><emphasis role="bold">If you are running kernel
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2.4:</emphasis><blockquote>
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<para>At both systems, ipsec0 would be included in
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/etc/shorewall/interfaces as a <quote>vpn</quote> interface:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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vpn ipsec0</programlisting>
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</blockquote></para>
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<para><emphasis role="bold">If you are running kernel
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2.6:</emphasis></para>
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<blockquote>
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<para><emphasis role="bold">It is essential that the
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<emphasis>vpn</emphasis> zone be declared before the
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<emphasis>net</emphasis> zone in
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<filename>/etc/shorewall/zones</filename>.</emphasis></para>
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<para>Remember the assumption that both systems A and B have eth0 as
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their internet interface.</para>
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<para>You must define the vpn zone using the /etc/shorewall/hosts
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file.</para>
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<para>/etc/shorewall/hosts - System A</para>
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<programlisting>#ZONE HOSTS OPTIONS
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vpn eth0:10.0.0.0/8</programlisting>
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<para>/etc/shorewall/hots - System B</para>
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<programlisting>#ZONE HOSTS OPTIONS
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vpn eth0:192.168.1.0/24</programlisting>
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<para>In addition, <emphasis role="bold">if you are using Masquerading
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or SNAT</emphasis> on your firewalls, you need to elmiinate the remote
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network from Masquerade/SNAT. These entries <emphasis
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role="bold">replace</emphasis> your current masquerade/SNAT entries for
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the local networks.</para>
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<para>/etc/shorewall/masq - System A</para>
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<programlisting>#INTERFACE SUBNET ADDRESS
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eth0:!10.0.0.0/8 192.168.1.0/24</programlisting>
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<para>/etc/shorewall/masq - System B</para>
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<programlisting>#INTERFACE SUBNET ADDRESS
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eth0:!192.168.1.0/24 10.0.0.0/8</programlisting>
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</blockquote>
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<para>You will need to allow traffic between the <quote>vpn</quote> zone
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and the <quote>loc</quote> zone -- if you simply want to admit all traffic
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in both directions, you can use the policy file:</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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loc vpn ACCEPT
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vpn loc ACCEPT</programlisting>
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<para></para>
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<para>Once you have these entries in place, restart Shorewall (type
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shorewall restart); you are now ready to configure the tunnel in <ulink
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url="http://www.xs4all.nl/%7Efreeswan/">FreeS/WAN</ulink>.</para>
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</section>
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<section id="Hub">
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<title>VPN Hub using Kernel 2.4</title>
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<para>Shorewall can be used in a VPN Hub environment where multiple remote
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networks are connected to a gateway running Shorewall. This environment is
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shown in this diatram.</para>
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<graphic fileref="images/ThreeNets.png" />
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<para>We want systems in the 192.168.1.0/24 sub-network to be able to
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communicate with systems in the 10.0.0.0/16 and 10.1.0.0/16 networks and
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we want the 10.0.0.0/16 and 10.1.0.0/16 networks to be able to
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communicate.</para>
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<para>To make this work, we need to do several things:</para>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>Open the firewall so that two IPSEC tunnels can be established
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(allow the ESP and AH protocols and UDP Port 500).</para>
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</listitem>
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<listitem>
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<para>Allow traffic through the tunnels two/from the local zone
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(192.168.1.0/24).</para>
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</listitem>
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<listitem>
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<para>Deny traffic through the tunnels between the two remote
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networks.</para>
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</listitem>
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</orderedlist>
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<para>Opening the firewall for the IPSEC tunnels is accomplished by adding
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two entries to the /etc/shorewall/tunnels file.</para>
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<para>In /etc/shorewall/tunnels on system A, we need the following</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 134.28.54.2
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ipsec net 130.252.100.14</programlisting>
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<para>In /etc/shorewall/tunnels on systems B and C, we would have:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 206.161.148.9</programlisting>
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<note>
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<para>If either of the endpoints is behind a NAT gateway then the
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tunnels file entry on the <emphasis role="bold">other</emphasis>
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endpoint should specify a tunnel type of <emphasis>ipsecnat</emphasis>
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rather than ipsec and the GATEWAY address should specify the external
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address of the NAT gateway.</para>
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</note>
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<para>On each system, we will create a zone to represent the remote
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networks. On System A:</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn1 ipv4
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vp2 ipv4</programlisting>
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<para>On systems B and C:</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn ipv4</programlisting>
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<para>At system A, ipsec0 represents two zones so we have the following in
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/etc/shorewall/interfaces:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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- ipsec0</programlisting>
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<para>The /etc/shorewall/hosts file on system A defines the two VPN
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zones:</para>
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<programlisting>#ZONE HOSTS OPTIONS
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vpn1 ipsec0:10.0.0.0/16
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vpn2 ipsec0:10.1.0.0/16</programlisting>
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<para>At systems B and C, ipsec0 represents a single zone so we have the
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following in /etc/shorewall/interfaces:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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vpn ipsec0</programlisting>
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<para>On systems A, you will need to allow traffic between the
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<quote>vpn1</quote> zone and the <quote>loc</quote> zone as well as
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between <quote>vpn2</quote> and the <quote>loc</quote> zone -- if you
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simply want to admit all traffic in both directions, you can use the
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following policy file entries on all three gateways:</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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loc vpn1 ACCEPT
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vpn1 loc ACCEPT
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loc vpn2 ACCEPT
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vpn2 loc ACCEPT</programlisting>
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<para>On systems B and C, you will need to allow traffic between the
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<quote>vpn</quote> zone and the <quote>loc</quote> zone -- if you simply
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want to admit all traffic in both directions, you can use the following
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policy file entries on all three gateways:</para>
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<para>/etc/shorewall/policy -- Systems B & C</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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loc vpn ACCEPT
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vpn loc ACCEPT</programlisting>
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<para>Once you have the Shorewall entries added, restart Shorewall on each
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gateway (type shorewall restart); you are now ready to configure the
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tunnels in <ulink
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url="http://www.xs4all.nl/%7Efreeswan/">FreeS/WAN</ulink>.</para>
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<note>
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<para>to allow traffic between the networks attached to systems B and C,
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it is necessary to simply add two additional entries to the
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/etc/shorewall/policy file on system A.</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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vpn1 vpn2 ACCEPT
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vpn2 vpn1 ACCEPT</programlisting>
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</note>
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<note>
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<para>If you find traffic being rejected/dropped in the OUTPUT chain,
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place the names of the remote VPN zones as a comma-separated list in the
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GATEWAY ZONE column of the /etc/shorewall/tunnels file entry.</para>
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</note>
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</section>
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<section id="RoadWarrior">
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<title>Mobile System (Road Warrior) Using Kernel 2.4</title>
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<para>Suppose that you have a laptop system (B) that you take with you
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when you travel and you want to be able to establish a secure connection
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back to your local network.</para>
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<graphic fileref="images/Mobile.png" />
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<example id="roadWarrior">
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<title>Road Warrior VPN</title>
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<para>You need to define a zone for the laptop or include it in your
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local zone. In this example, we'll assume that you have created a zone
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called <quote>vpn</quote> to represent the remote host.</para>
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<para>/etc/shorewall/zones - System A</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn ipv4</programlisting>
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<para>In this instance, the mobile system (B) has IP address 134.28.54.2
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but that cannot be determined in advance. In the /etc/shorewall/tunnels
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file on system A, the following entry should be made:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 0.0.0.0/0</programlisting>
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<para><note>
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<para>the GATEWAY ZONE column contains the name of the zone
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corresponding to peer subnetworks. This indicates that the gateway
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system itself comprises the peer subnetwork; in other words, the
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remote gateway is a standalone system.</para>
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</note></para>
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<para>You will need to configure /etc/shorewall/interfaces and establish
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your <quote>through the tunnel</quote> policy as shown under the first
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example above.</para>
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</example>
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</section>
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<section id="Dynamic">
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<title>Dynamic RoadWarrior Zones</title>
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<para>Beginning with Shorewall release 1.3.10, you can define multiple VPN
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zones and add and delete remote endpoints dynamically using
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/sbin/shorewall. With Shorewall 2.0.2 Beta 1 and later versions, this
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capability must be enabled by setting DYNAMIC_ZONES=Yes in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf</ulink>.<important>
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<para>DYNAMIC_ZONES=Yes is not supported by Shorewall-perl 4.2.0 or
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later versions. Use <ulink url="ipsets.html#Dynamic">dynamic zones
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defined by ipsets</ulink> instead.</para>
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</important></para>
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<para>In /etc/shorewall/zones:</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn1 ipv4
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vpn2 ipv4
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vpn3 ipv4</programlisting>
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<para>In /etc/shorewall/tunnels:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 0.0.0.0/0 vpn1,vpn2,vpn3</programlisting>
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<para>When Shorewall is started, the zones vpn[1-3] will all be empty and
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Shorewall will issue warnings to that effect. These warnings may be safely
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ignored. FreeS/Wan may now be configured to have three different Road
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Warrior connections with the choice of connection being based on X-509
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certificates or some other means. Each of these connectioins will utilize
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a different updown script that adds the remote station to the appropriate
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zone when the connection comes up and that deletes the remote station when
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the connection comes down. For example, when 134.28.54.2 connects for the
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vpn2 zone the <quote>up</quote> part of the script will issue the
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command:</para>
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<programlisting>/sbin/shorewall add ipsec0:134.28.54.2 vpn2</programlisting>
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<para>and the <quote>down</quote> part will:</para>
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<programlisting>/sbin/shorewall delete ipsec0:134.28.54.2 vpn2</programlisting>
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</section>
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</article> |