forked from extern/shorewall_code
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git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@1558 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
348 lines
13 KiB
XML
348 lines
13 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 using Linux Kernel 2.6</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>2004-08-18</pubdate>
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<copyright>
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<year>2004</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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<warning>
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<para>To use this support, your kernel and iptables must include the
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Netfilter+ipsec patches and policy match support and you must be running
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Shorewall 2.1.4 or later.</para>
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</warning>
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<warning>
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<para>As of this writing, the Netfilter+ipsec and policy match support are
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broken when used with a bridge device. The problem has been reported to
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the responsible Netfilter developer who has confirmed the problem.</para>
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</warning>
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<section>
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<title>Shorewall 2.1 and Kernel 2.6 IPSEC</title>
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<para>The 2.6 Linux Kernel introduces new facilities for defining
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encrypted communication between hosts in a network. The network
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administrator defines a set of Security Policies which are stored in the
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kernel as a Security Policy Database (SPD). Outgoing traffic is encrypted
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according to the contents of the SPD and incoming traffic is verified
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against the SPD to ensure that no unencrypted traffic is accepted in
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violation of the administrator's policies.</para>
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<para>There are three ways in which IPSEC traffic can interact with
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Shorewall policies and rules:</para>
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<orderedlist>
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<listitem>
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<para>Traffic that is encrypted on the firewall system. The traffic
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passes through Netfilter twice -- first as unencrypted then
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encrypted.</para>
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</listitem>
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<listitem>
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<para>Traffic that is decrypted on the firewall system. The traffic
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passes through Netfilter twice -- first as encrypted then as
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unencrypted.</para>
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</listitem>
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<listitem>
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<para>Encrypted traffic that is passed through the firewall system.
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The traffic passes through Netfilter once.</para>
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</listitem>
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</orderedlist>
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<para>In cases 1 and 2, the encrypted traffic is handled by entries in
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<filename>/etc/shorewall/tunnels</filename> (don't be mislead by the name
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of the file -- <emphasis>transport mode</emphasis> encrypted traffic is
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also handled by entries in that file). The unencrypted traffic is handled
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by normal rules and policies.</para>
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<para>Under the 2.4 Linux Kernel, the association of unencrypted traffic
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and zones was made easy by the presense of IPSEC pseudo-interfaces with
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names of the form <filename class="devicefile">ipsecn</filename> (e.g.
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<filename class="devicefile">ipsec0</filename>). Outgoing unencrypted
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traffic (case 1.) was send through an <filename
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class="devicefile">ipsecn</filename> device while incoming unencrypted
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traffic (case 2) arrived from an <filename
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class="devicefile">ipsecn</filename> device. The 2.6 kernel-based
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implementation does away with these pseudo-interfaces. Outgoing traffic
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that is going to be encrypted and incoming traffic that has been decrypted
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must be matched against policies in the SPD.</para>
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<para></para>
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</section>
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<section>
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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 <filename>/etc/shorewall/tunnels</filename> file.</para>
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<para>In <filename>/etc/shorewall/tunnels</filename> on system A, we need
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the following</para>
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<blockquote>
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<para><filename>/etc/shorewall/tunnels</filename> — System A:</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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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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<para><filename>/etc/shorewall/tunnels</filename> — System B:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 206.161.148.9
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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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.</para>
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<blockquote>
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<para><filename>/etc/shorewall/zones</filename> — Systems A and
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B:</para>
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<programlisting>#ZONE DISPLAY COMMENTS
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net Internet The big bad internet
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vpn VPN Virtual Private Network
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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<para>Remember the assumption that both systems A and B have eth0 as their
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internet interface.</para>
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<para>You must define the vpn zone using the
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<filename>/etc/shorewall/hosts</filename> file.</para>
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<blockquote>
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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 <emphasis role="bold">ipsec</emphasis>
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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<para>/etc/shorewall/hosts — System B</para>
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<programlisting>#ZONE HOSTS OPTIONS
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vpn eth0:192.168.1.0/24 <emphasis role="bold">ipsec</emphasis>
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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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 IPSEC.</para>
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</section>
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<section>
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<title>Mobile System (Road Warrior)</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>
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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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<blockquote>
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<para>/etc/shorewall/zones — System A</para>
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<programlisting>#ZONE DISPLAY COMMENTS
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net Internet The big bad internet
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vpn VPN Road Warriors
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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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
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<filename>/etc/shorewall/tunnels</filename> file on system A, the
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following entry should be made:<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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ipsec net 0.0.0.0/0 vpn
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote></para>
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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>The VPN zone is defined using the /etc/shorewall/hosts
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file:</para>
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<blockquote>
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<para>/etc/shorewall/hosts — System A:</para>
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<programlisting>#ZONE HOSTS OPTIONS
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vpn eth0:0.0.0.0/0 <emphasis role="bold"> ipsec</emphasis>
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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<para>You will need to configure your <quote>through the tunnel</quote>
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policy as shown under the first example above.</para>
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</example>
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</section>
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<section>
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<title>Transport Mode</title>
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<para>In today's wireless world, it is often the case that individual
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hosts in a network need to establish secure connections with the other
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hosts in that network. In that case, IPSEC transport mode is an
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appropriate solution.</para>
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<para><graphic fileref="images/TransportMode.png" />Here's an example
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using the ipsec-tools package. The files shown are from host
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192.168.20.10; the configuration of the other nodes is similar.</para>
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<blockquote>
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<para><filename>/etc/racoon/racoon.conf</filename>:</para>
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<programlisting>path pre_shared_key "/etc/racoon/psk.txt" ;
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remote anonymous
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{
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exchange_mode aggressive ;
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my_identifier user_fqdn "teastep@shorewall.net" ;
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lifetime time 24 hour ;
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proposal {
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encryption_algorithm 3des;
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hash_algorithm sha1;
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authentication_method pre_shared_key ;
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dh_group 2 ;
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}
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}
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sainfo anonymous
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{
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pfs_group 2;
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lifetime time 12 hour ;
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encryption_algorithm 3des, blowfish, des, rijndael ;
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authentication_algorithm hmac_sha1, hmac_md5 ;
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compression_algorithm deflate ;
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}
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</programlisting>
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<para><filename>/etc/racoon/setkey.conf</filename>:</para>
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<programlisting># First of all flush the SPD database
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spdflush;
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# Add some SPD rules
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spdadd 192.168.20.10/32 192.168.20.20/32 any -P out ipsec esp/transport/192.168.20.10-192.168.20.20/require;
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spdadd 192.168.20.20/32 192.168.20.10/32 any -P in ipsec esp/transport/192.168.20.20-192.168.20.10/require;
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spdadd 192.168.20.10/32 192.168.20.30/32 any -P out ipsec esp/transport/192.168.20.10-192.168.20.30/require;
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spdadd 192.168.20.30/32 192.168.20.10/32 any -P in ipsec esp/transport/192.168.20.30-192.168.20.10/require;
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spdadd 192.168.20.10/32 192.168.20.40/32 any -P out ipsec esp/transport/192.168.20.10-192.168.20.40/require;
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spdadd 192.168.20.40/32 192.168.20.10/32 any -P in ipsec esp/transport/192.168.20.40-192.168.20.10/require;
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</programlisting>
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<para>/etc/racoon/psk.txt:</para>
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<programlisting>teastep@shorewall.net <key></programlisting>
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</blockquote>
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<para>Shorewall configuration goes as follows:</para>
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<blockquote>
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<para><filename>/etc/shorewall/zones</filename>:</para>
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<programlisting>#ZONE DISPLAY COMMENTS
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loc Local Local Network
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net Net Internet
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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<para><filename>/etc/shorewall/interfaces</filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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net eth0 detect routefilter,dhcp,tcpflags
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#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
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<para><filename>/etc/shorewall/hosts</filename>:</para>
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<programlisting>#ZONE HOST(S) OPTIONS
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loc eth0:192.168.20.0/24 ipsec
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#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS LINE -- DO NOT REMOVE</programlisting>
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<para><filename>/etc/shorewall/policy</filename>:</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL LIMIT:BURST
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fw all ACCEPT
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loc fw ACCEPT
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net loc NONE
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loc net NONE
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net all DROP info
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# The FOLLOWING POLICY MUST BE LAST
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all all REJECT info
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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<para>Since there are no cases where net<->loc traffic should
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occur, NONE policies are used.</para>
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</blockquote>
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</section>
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</article> |