[l2tpns.git] / Docs / vpn / practical-vpns.xml

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<article>
  <articleinfo>
    <title>Practical VPNs</title>
    <subtitle>Implementing Full-scale VPNs</subtitle>

    <author>
      <firstname>Liran</firstname>
      <surname>Tal</surname>
      <affiliation>
        <address>
          <email>liran@enginx.com</email>
        </address>
      </affiliation>
    </author>

    <othercredit>
      <firstname>Yakov</firstname>
      <surname>Shtutz</surname>
      <contrib>Special thanks</contrib>
    </othercredit>

    <othercredit>
      <firstname>Shahar</firstname>
      <surname>Fermon</surname>
      <contrib>Testing and feedback</contrib>
    </othercredit>

    <abstract>
      <para>
        This document was compiled from the administrator's point of
        view, to explain what are VPNs, how they are deployed today
        and to detail the necessary steps and tools to achieve and
        create a fully working VPN solution, integrated with RADIUS
        systems for AAA.
      </para>

      <para>
        I will not dwell in this document on how to compile source
        packages or kernel patching, and with the same tone I'm
        assuming the reader is an exprerienced Linux user.
      </para>

      <para>
        VPNs have their share amount of gossip for being a very
        complex thing, and in some cases this may be true as they tend
        to be more security intenssive which require adding more and
        more layers to the scheme.  With this said, we'll take a look
        at how fairly straight-forward it is to setup VPNs and
        maintain them with varius Open-Source tools.
      </para>
    </abstract>
  </articleinfo>

  <sect1 id="overview">
    <title>Overview of VPNs and IPsec</title>
    <sect2 id="vpns">
      <title>Virtual Private Networks</title>
      <para>
        The purpose of a VPN is to create a secure channel ontop of an
        un-secure medium, where a computer or a device are put in each
        end-point in order to establish communication, each of these
        end-points are often reffered to as Point of Presense, or POP.
        This kind of a communication allows the capability of creating
        a Virtual Private Network, which is accesable over a medium
        such as the Internet and thus, extend the physical boundaries
        of an existing local network.
      </para>

      <para>
        VPNs have three forms:
        <variablelist>
          <varlistentry>
            <term>Site-To-Site VPNs</term>
            <listitem>
              <para>
                these setups exist in order to extend the local network
                to create a much bigger LAN over the Internet.
              </para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Network-To-Host or Remote access VPNs</term>
            <listitem>
              <para>
                where a central VPN server is able to achieve multiple
                connections, often reffered to as RoadWarrior VPNs.
                (This setup is very common among ISPs)
              </para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>Network-To-Network</term>
            <listitem>
              <para>
                extranet VPNs allow secure connections within branches
                and business partners, they are an extension of a
                Site-To-Site VPNs.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>
      </para>

      <para>
        <xref linkend="site-to-site"/> shows a Site-To-Site VPN diagram.
        <figure id="site-to-site" float="1">
          <title>Site to Site VPN</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="site-to-site-vpn.png"/>
            </imageobject>
          </mediaobject>
        </figure>
      </para>

      <para>
        IP/VPNs are connections which are based upon IP tunnels.  A
        tunnel is a way to encapsulate an IP packet inside another IP
        packet or some other type of packet.  Why do we need
        tunneling?  A Virtual Private Network is identified by IANA's
        private IP assignments and so such packet can not go beyond
        the uplink Internet interface.
      </para>

      <para>
        <xref linkend="tunneling-process"/> shows the tunneling process.
        <figure id="tunneling-process" float="1">
          <title>Tunneling Process</title>
          <mediaobject>
            <imageobject>
              <imagedata fileref="tunneling-process.png"/>
            </imageobject>
          </mediaobject>
        </figure>
      </para>

      <para>
        Several tunneling protocols are available for manifesting
        VPNs.

        <variablelist>
          <varlistentry>
            <term>L2F</term>
            <listitem>
              <para>
                Layer 2 Forwarding, an older implementation which
                assume position at the link layer of the OSI.  It has
                no encryption capabilities and hence, deprecated.
              </para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>L2TP</term>
            <listitem>
              <para>
                Layer 2 Tunneling Protocol, still no encryption
                capabilities.
              </para>
            </listitem>
          </varlistentry>

          <varlistentry>
            <term>PPTP</term>
            <listitem>
              <para>
                Point-to-Point Tunneling Protocol, and yet again, no
                encryption.
              </para>
            </listitem>
          </varlistentry>
        </variablelist>
      </para>

      <para>
        As seen, the requirement of encryption enhancement is urgent
        in order to assure authentication, data integrity and privacy.
        IPsec solves this by providing a suite of security measures
        implemented at layer 3.
      </para>
    </sect2>

    <sect2 id="ipsec">
      <title>IP Security Suite (IPsec)</title>
      <para>
        VPN Security is now appearing, this complex things.  How so?
        VPN tunnels by themselves are easily maintained by
        single-standalone tools like pppd, l2tpns, stunnel and others.
        Involving security with VPNs though requires more:

        <itemizedlist>
          <listitem>
            <para>authentication, data integrity and privacy</para>
          </listitem>

          <listitem>
            <para>keying management</para>
          </listitem>
        </itemizedlist>
      </para>

      <note>
        <para>
          Keys are secrets being shared by two end-points to provide a
          secure mean of communication against a third-party
          connection from sniffing the actual data.
        </para>
      </note>

      <para>
        Different ways to handle key management include RADIUS (Remote
        Authentication Dial In User Service) systems which provide AAA
        (Authentication, Authorization and Accounting).  Another
        solution is ISAKMP/Oackly - Internet Security Association and
        Key Management Protocol.  This solution requires you to posess
        one of the following:

        <itemizedlist>
          <listitem>
            <para>something you have</para>
          </listitem>

          <listitem>
            <para>something you know</para>
          </listitem>

          <listitem>
            <para>something you are</para>
          </listitem>
        </itemizedlist>
      </para>

      <para>
        The more requirements you meet the more secure is the medium,
        once established.  Let's review, something we have is like a
        certificate, it proves who we are.  Something we know, is a
        key, a secret password which we were told in a whisper, and
        something we are is our-fingerprint which identifies ourselves
        from other individuals.
      </para>

      <sect3 id="ipsec-in-depth">
        <title>IPsec in Depth</title>
        <para>
          IPsec consists of two main protocols, an Authentication
          Header and Encapsulation Security Payload, also known as AH
          and ESP.  Although it is not bound to these and can be
          extended (and often is) to other standarts such as

          <itemizedlist>
            <listitem>
              <para>Data Encryption Standart (DES and 3DES)</para>
            </listitem>

            <listitem>
              <para>Diffie-Hellman (DH)</para>
            </listitem>

            <listitem>
              <para>Secure Hash Algorithm-1 (SHA1)</para>
            </listitem>

            <listitem>
              <para>Message Digest 5 (MD5)</para>
            </listitem>

            <listitem>
              <para>Internet Key Exchange (IKE)</para>
            </listitem>

            <listitem>
              <para>Certification Authorities (CA)</para>
            </listitem>
          </itemizedlist>
        </para>

        <para>
          We'll be deploying an IKE daemon to handle the key
          management, which uses the Diffie- Hellman cryptography
          protocol in order to allow two parties to establish a
          connection based upon a shared secret key that both parties
          posess.  (Authentication within IKE is handled by MD5
          hashing)
        </para>

        <para>
          IKE is responsible for authentication of two IPsec parties,
          negotiation of keys for encryption algorithms and security
          associations.  This process is commonly regarded as two
          phases:

          <variablelist>
            <varlistentry>
              <term>Phase 1: IKE Security Association</term>
              <listitem>
                <para>
                  The IKE daemon authenticates against the peers in
                  order to achieve a secure channel, according to the
                  Diffie-Hellman key agreement.
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>Phase 2: IKE IPsec Negotiation</term>
              <listitem>
                <para>
                  After achieving an authenticated channel, the
                  parties now negotiate a secure transform (the way to
                  encrypt and secure the medium) where the sender is
                  offering his/hers transform set after which the
                  receiver decides upon one.  An IPsec session can now
                  safely begin.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>
        </para>

        <para>
          Just to be clear, a Security Association is an agreed
          relation between two parties which describes how they will
          use security services (from IPsec) to communicate.
        </para>
      </sect3>

      <sect3 id="ipsec-modes">
        <title>IPsec Modes</title>
        <para>
          IPsec can operate in two different modes:

          <variablelist>
            <varlistentry>
              <term>Transport mode</term>
              <listitem>
                <para>
                  takes place when two devices (like a station and a
                  gateway (now considered a host)) are establishing a
                  connection which upon they both support IPsec.
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>Tunnel mode</term>
              <listitem>
                <para>
                  we require tunnel mode when we proxy IPsec
                  connetions between two stations behind the IPsec
                  gateway.  For example, in a Site-to-Site VPN a
                  tunnel mode lives, since it exists in order to
                  provide the stations behind these gateways runing
                  the VPN/IPsec to communicate securely.  In this
                  situation, both end-points are runing an IPsec
                  software.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>
        </para>

        <para>
          In definition, a tunnel mode IPsec is better secured than
          transport.  Without going too deep into the ins-and-outs of
          the technical side, transport mode doesn't encapsulate the
          actual IP layer but only the tcp/udp (Transport layer of the
          OSI) where-as a tunnel mode encapsulate both the Transport
          layer and the IP layer into a new IP packet.
        </para>

        <para>
          To summarize, we need VPNs for data-exchange methods and a
          set of IPsec tools for security reasons.
        </para>
      </sect3>
    </sect2>
  </sect1>

  <sect1 id="deployment">
    <title>VPN Deployment</title>
    <para>
      I've assembled another diagram to view the actual VPN setup.
      <xref linkend="vpn-deployment"/> gives a general description of
      how the network will be layed out in real-world scenario.

      <figure id="vpn-deployment" float="1">
        <title>VPN Deployment</title>
        <mediaobject>
          <imageobject>
            <imagedata fileref="vpn-deployment.png"/>
          </imageobject>
        </mediaobject>
      </figure>
    </para>

    <para>
      We notice that a single Linux box is acting as a Gateway and has
      all the services included with it.  This is a bad idea from a
      security prespective but it's easy to just deploy the FreeRADIUS
      and MySQL servers on another machine.  Of course the L2TPns and
      the rest of the IPsec tools suite would have to remain on the
      Gateway box (not necessarily the Firewall).
    </para>

    <para>
      <xref linkend="vpn-process"/> attempts to explain the actual
      process that the VPN takes and to detail the place that each of
      that application-in-charge takes place.

      <figure id="vpn-process" float="1">
        <title>VPN Process</title>
        <mediaobject>
          <imageobject>
            <imagedata fileref="vpn-process.png"/>
          </imageobject>
        </mediaobject>
      </figure>
    </para>

    <sect2 id="deployment-requirements">
      <title>Requirements</title>
      <sect3 id="deployment-requirements-toolbox">
        <title>The Toolbox</title>
        <para>
          Following is a description of the requirements you will
          have to meet:

          <variablelist>
            <varlistentry>
              <term>A Linux box</term>
              <listitem>
                <para>preferably a 2.4.27 kernel or higher.</para>
                <para>
                  Debian is the chosen distribution which means we'll
                  be using apt-get for installation, but I'll also
                  focus on basic source tarballs installation.
                </para>

                <para>
                  Dependencies:

                  <itemizedlist>
                    <listitem>
                      <para>ipsec configuration in the kernel</para>
                    </listitem>
                  </itemizedlist>
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>L2TPns</term>
              <listitem>
                <para>an L2TP PPP Termination tool.</para>
                <para>
                  Dependencies:

                  <itemizedlist>
                    <listitem>
                      <para>libcli 1.8.0 or greater</para>
                    </listitem>

                    <listitem>
                      <para>
                        tun/tap interface compiled in the kernel or as
                        a module
                      </para>
                    </listitem>
                  </itemizedlist>
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>FreeRADIUS</term>
              <listitem>
                <para>For authentication, and accounting.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>MySQL</term>
              <listitem>
                <para>To act as a back-end database for the RADIUS.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term>OpenSwan</term>
              <listitem>
                <para>Provides the ipsec suite package.</para>
              </listitem>
            </varlistentry>
          </variablelist>
        </para>
      </sect3>

      <sect3 id="deployment-requirements-kernel">
        <title>Kernel Support</title>
        <para>
          Debian stock kernel 2.4.27 and up are ipsec compatible
          although if you think otherwise check for the
          kernel-patch-openswan package.
        </para>
      </sect3>
    </sect2>

    <sect2 id="deployment-installation">
      <title>Installation</title>
      <sect3 id="deployment-installation-l2tpns">
        <title>L2TPns</title>
        <sect4 id="deployment-installation-l2tpns-install">
          <title>Installation</title>
          <blockquote>
            <para>
              L2TPns is a layer 2 tunneling protocol network server
              (LNS).  It supports up to 65535 concurrent sessions per
              server/cluster plus ISP features such as rate limiting,
              walled garden, usage accounting, and more.
            </para>
          </blockquote>

          <para>
            In a personal note - L2TPns is highly configurable for
            many cases, and extremely reliable for
            production/commerical use.
          </para>

          <para>
            <variablelist>
              <varlistentry>
                <term>Step 1:</term>
                <listitem>
                  <para>
                    Make sure you have libcli-1.8 development package
                    installed:
<screen>
# apt-cache search libcli
libcli-dev - emulates a cisco style telnet command-line interface (dev files)
libcli1 - emulates a cisco style telnet command-line interface
# apt-get install libcli-dev
</screen>
                  </para>
                </listitem>
              </varlistentry>

              <varlistentry>
                <term>Step 2:</term>
                <listitem>
                  <para>
                    Download the source from
                    <ulink url="http://sourceforge.net/projects/l2tpns/">
                    SourceForge</ulink>.
                  </para>
                </listitem>
              </varlistentry>

              <varlistentry>
                <term>Step 3:</term>
                <listitem>
                  <para>
                    Build and install:
                    <code>make &amp;&amp; make install</code>
                  </para>
                </listitem>
              </varlistentry>
            </variablelist>
          </para>

          <note>
            <para>
              Alternately, you can skip these steps and simply
              <code>apt-get install l2tpns</code>.
            </para>
          </note>

          <note>
            <para>
              On RPM-based distributions, you should be able to make
              packages from the libcli and l2tpns source tarballs with
              <code>rpmbuild -ta</code>.
            </para>
          </note>

          <para>
            Once compiliation is done you will have l2tpns in
            <filename>/usr/sbin/l2tpns</filename>, and all
            configuration files can be found in
            <filename>/etc/l2tpns/</filename>.
          </para>
        </sect4>

        <sect4 id="deployment-installation-l2tpns-config">
          <title>Configuration</title>
          <para>
            The only configuration that L2TPns takes is centralized in
            the configuration file
            <filename>/etc/l2tpns/startup-config</filename>.
<programlisting>
set debug 2                               # Debugging level
set log_file "/var/log/l2tpns"            # Log file: comment out to use stderr, use
                                          # "syslog:facility" for syslog
set pid_file "/var/run/l2tpns.pid"        # Write pid to this file
set l2tp_secret <emphasis>"secret"</emphasis>                  # shared secret
set primary_dns <emphasis>212.117.128.6</emphasis>             # Only 2 DNS server entries are allowed
set secondary_dns <emphasis>212.117.129.3</emphasis>
set primary_radius <emphasis>192.168.0.1</emphasis>            # Can have multiple radius server entries,
                                          # but ony one radius secret
set primary_radius_port 1812
set radius_secret <emphasis>"radius_secret"</emphasis>
set radius_accounting yes
set radius_dae_port 3799
set accounting_dir "/var/run/l2tpns/acct" # Write usage accounting files into specified
                                          # directory
set peer_address <emphasis>192.168.0.1</emphasis>              # Gateway address given to clients
load plugin "sessionctl"                  # Drop/kill sessions
load plugin "autothrottle"                # Throttle/snoop based on RADIUS
load plugin "throttlectl"                 # Control throttle/snoop with nsctl
load plugin "snoopctl"
</programlisting>
          </para>

          <para>
            This is the trimmed down version of probably most of
            the common configuration and even some extra options.
          </para>

          <para>
            Important configuration options are highlited and you
            should adjust these to meet your network needs.  We can
            deploy all of the environment into one box which is of
            course not a very good idea from a security point of view,
            but will function just fine.  Moreover, we will be using
            aliased IP addresses so once you've decided to move the
            FreeRADIUS daemon to another computer on the LAN it will
            be fairly easy and won't take too much configuration into
            it.
          </para>

          <para>
            Next, we need to setup the IP pool that L2TPns will
            provide to each VPN client.  The configuration file is
            located at <filename>/etc/l2tpns/ip_pool</filename> and
            should look like the following:
            <programlisting>172.16.21.0/24</programlisting>
          </para>

          <important>
            <para>
              Of course you can change this pool to anything else
              (IANA IPs assigned for private internets only) just make
              sure it is not conflicting with your current LAN network
              addresses.  This means that if you've assigned addresses
              of 192.168.0.1 and 192.168.0.2 to your LAN boxes you
              can't have a pool of 192.168.0.1/24 defined since L2TPns
              will try to route those addresses from the tun device,
              which is needless to say a bad idea...
            </para>
          </important>

          <para>Next up, creating the access-list for L2TPns.</para>

          <para>
            Add a username and password into
            <filename>/etc/l2tpns/users</filename>:
            <programlisting>admin:12345</programlisting>

            The password may either be plain-text as above, or
            encrypted with MD5 or DES (to distinguish DES from
            plain-text passwords, prefix the value with
            <code>{crypt}</code>).
          </para>

          <para>
            L2TPns utilizes a terminal connection on port 23 which you
            would feel very comfortable in if you have worked with
            routers and switches devices before.  The terminal
            provides control over the ppp termination which is why
            we've created an account to log on to.
          </para>
        </sect4>
      </sect3>

      <sect3 id="deployment-installation-ipsec">
        <title>IPsec</title>
        <sect4 id="deployment-installation-ipsec-install">
          <title>Installation</title>
          <para>
            User-space IPsec tools for various IPsec implementations
            exist for linux, among them is the port of KAME's
            libipsec, setkey, and racoon.  Others are the OpenSWAN (a
            successor to the FreeSWAN project).
          </para>

          <para>
            Getting IPsec installed is fairly easy with Debian:
            <screen># apt-get install openswan</screen>
          </para>

          <para>
            The OpenSWAN project provides packages for RPM-based
            distributions.
          </para>

          <para>
            Alternately, you may download the
            <ulink url="http://www.openswan.org/code/">source</ulink>
            from the OpenSWAN project:
<screen>
# tar xvzf openswan-2.4.4.tar.gz
# cd openswan-2.4.4
# ./configure &amp;&amp; make &amp;&amp; make install
</screen>
          </para>
        </sect4>

        <sect4 id="deployment-installation-ipsec-config">
          <title>Configuration</title>
          <para>
            OpenSWAN acts as the IKE daemon (remember IKE?  it's job
            is to authenticate between the two peers and negotiate a
            secure medium).  We will be setting up the IKE daemon as a
            RoadWarrior configuration, a term for remote access
            VPNs.
          </para>

          <para>
            We desire this approach for compatibilty because after our
            VPN solution will be complete any user from a Windows
            machine will be easily ready to connect without any 3rd
            party applications, same for Linux.
          </para>

          <para>
            Configuration files are placed in
            <filename>/etc/ipsec.d/</filename>,
            <filename>/etc/ipsec.conf</filename> and
            <filename>/etc/ipsec.secrets</filename>.
          </para>

          <para>
            Let's start by choosing the remote client and it's PSK
            (Private Shared Key) <filename>/etc/ipsec.secrets</filename>:
<programlisting>
hostname_or_ipaddress %any : PSK "mysecretkeyisverylong"
</programlisting>
          </para>

          <para>
            This is an IP/key pair.  The IP or FQDN defines the local
            peer (like a SOHO branch), then the remote host.  Here we
            defined %any for all hosts, though it's possible to define
            only a specific IP.  At last, we define the key associated
            with it.
          </para>

          <para>
            A better way to create a key is to utilize /dev/random for
            creating a unique key.
            <screen># dd if=/dev/random count=16 bs=1 2>/dev/null | xxd -ps</screen>
          </para>

          <para>
            Next, let's prepare the configuration file
            <filename>/etc/ipsec.conf</filename>:
<programlisting>
version 2.0
config setup
     nat_traversal=yes

conn l2tp
     authby=secret
     pfs=no
     keyingtries=3
     left=real_ip_address
     leftnexthop=%defaultroute
     leftprotoport=17/%any
     right=%any
     rightprotoport=17/%any
     auto=add

include /etc/ipsec.d/examples/no_oe.conf
</programlisting>
          </para>

          <para>
            In this file we have first defined version 2 which is a
            must, then enabled NAT Traversal.  To understand the
            importance of this feature think of the following
            scenario:  A remote user attempts to connect while he's
            behind a router and therefore NATed.  The router has to
            de-encapsulate the packet, change things and then build it
            up again and send it.  IPsec doesn't like other people
            messing with it's packet.  That's why we solve this issue
            with NAT Traversal.
          </para>

          <para>
            Next up we configure authentication type (certificates,
            psk, rsa keys, etc) then the left and right peers.  The
            default mode OpenSWAN takes is tunnel unless told
            otherwise.  I won't go into in-depth explanation of every
            method, you can take a quick look at
            <filename>/etc/ipsec.d/examples</filename> for more
            explanation and other variations of working with RSA keys,
            Certificates, host-to-host, and more.
          </para>

          <para>
            In summary:
            <itemizedlist>
              <listitem>
                <para>
                  We've configured an almost complete IPsec VPN setup.
                </para>
              </listitem>

              <listitem>
                <para>
                  We've installed and configured a VPN server (L2TPns)
                  and our IPsec security suite.
                </para>
              </listitem>

              <listitem>
                <para>
                  To control both of them we use:
                  <filename>/etc/init.d/l2tpns</filename> and
                  <filename>/etc/init.d/racoon</filename> (location
                  of start-up scripts may vary on non-Debian systems,
                  or if you've installed from
                  source).
                </para>
              </listitem>
            </itemizedlist>
          </para>
        </sect4>
      </sect3>

      <sect3 id="deployment-installation-freeradius">
        <title>FreeRADIUS</title>
        <para>
          The VPN setup needs to authenticate against something, that
          is the users database which we chose to be a FreeRADIUS
          server backed with a MySQL database.
        </para>

        <sect4 id="deployment-installation-freeradius-install">
          <title>Installation</title>
          <blockquote>
            <para>
              FreeRADIUS is the premiere open source RADIUS server.
              While detailed statistics are not available, we believe
              that FreeRADIUS is well within the top 5 RADIUS servers
              world-wide, in terms of the number of people who use it
              daily for authentication.  It scales from embedded
              systems with small amounts of memory, to systems with
              millions of users.  It is fast, flexible, configurable,
              and supports more authentication protocols than many
              commercial servers.
            </para>
          </blockquote>

          <para>
            Installing on Debian:
            <screen># apt-get install freeradius freeradius-mysql</screen>
          </para>

          <para>
            From source:  Download the latest freeradius package from
            <ulink url="http://freeradius.org/getting.html">freeradius.org
            </ulink>
<screen>
# tar xvzf freeradius.tar.gz
# cd freeradius
# ./configure &amp;&amp; make &amp;&amp; make install
</screen>
          </para>
        </sect4>

        <sect4 id="deployment-installation-freeradius-config">
          <title>Configuration</title>
          <para>
            This will appear a bit complex but it isn't, it's just a
            lot of configuration.
          </para>

          <para>
            Following are the configurations you need to have in your
            <filename>/etc/freeradius/</filename> files.
          </para>

          <para>
            In this section I will not give you a dump of the
            configuration since they are very long and mostly default.
            I'll just post which changes to make.
          </para>

          <para>
            We haven't yet configured MySQL, but it'll come
            afterwards, don't worry.
          </para>

          <para>
            Make the following changes to the file
            <filename>/etc/freeradius/sql.conf</filename>:
<programlisting>
server = "192.168.0.1"
login = "radius"
password = "12345678"</programlisting>
          </para>

          <para>
            Add the following to the file
            <filename>/etc/freeradius/clients.conf</filename>:
<programlisting>
client 192.168.0.1 {
        secret    = my_secret
        shortname = localhost
        nastype   = other
}
</programlisting>
          </para>

          <para>
            Don't confuse the secret directive there with IPsec.
            RADIUS server are using secret keys also to identify their
            allowed NAS (Network Access Servers), these are the
            clients that talk to the RADIUS server.
          </para>

          <para>
            Also, change the <code>client 127.0.0.1 {}</code>
            directive to hold the secret "my_secret" like we
            configured for 192.168.0.1 to avoid conflicts.
          </para>

          <para>
            Uncomment the <code>sql</code> directive in the
            <code>authorize</code>, <code>accounting</code>, and
            <code>session</code> sections of
            <filename>/etc/freeradius/radiusd.conf</filename>.
          </para>

          <para>
            Now for populating FreeRADIUS with MySQL.  If you don't
            know or haven't set root password for MySQL you can do it
            now with:
            <screen># mysqladmin -u root password password_here</screen>

            Then add the following to
            <filename>/root/.my.cnf</filename>:

<programlisting>
[mysqladmin]
user = root
password = password_here
</programlisting>
          </para>

          <para>
            Create the <code>radius</code> database, using the
            schema given in
            <filename>/usr/share/doc/freeradius/examples/db_mysql.sql.gz
            </filename>.
          </para>

          <note>
            <para>
              It may be necessary to modify the column definition of
              <code>id</code> in the <code>nas</code> table, removing
              <code>DEFAULT '0'</code> such that the definition reads:

              <programlisting>id int(10) NOT NULL auto_increment,</programlisting>
            </para>
          </note>

          <screen>
# mysqladmin create radius
# mysql radius
mysql> source db_mysql.sql
mysql> GRANT ALL ON * TO 'radius'@'localhost' IDENTIFIED BY 'radius_password';
</screen>
          <para>
            All the configuration is now done.  Let's add a user to
            our VPN database.
<screen>
# mysql radius
mysql> INSERT INTO radcheck values (0, "test", "User-Password", "==", "1234");
</screen>
          </para>

          <para>
            We have now created a user in the database of username
            <code>test</code> and password <code>1234</code>.
          </para>

          <para>
            Testing the RADIUS setup is simple using the radtest
            utility provided with it.
<screen>
# radtest
Usage: radtest user passwd radius-server[:port] nas-port-number secret [ppphint] [nasname]
# radtest test 1234 192.168.0.1 1812 my_secret
</screen>
          </para>

          <para>
            radtest sends an Access-Request to the RADIUS server and
            expects an Access-Accept back from it.  If you're not
            getting an Access-Accept from the RADIUS you're advised to
            check the configuration again and see what you might have
            missed.
          </para>
        </sect4>
      </sect3>

      <sect3 id="deployment-installation-firewall">
        <title>Firewall Configuration</title>
        <para>
          We need to apply a few things to iptables configuration and
          kernel networking.
        </para>

        <para>
          First off, we need to accept VPN-specific packets through
          the firewall.  Of course you will have to adjust the rules
          to fits you needs, in this case, ppp0 is the Internet
          interface.
<screen>
# iptables --append INPUT --in-interface  ppp0 -p udp --dport 1701 -j ACCEPT
# iptables --append INPUT --in-interface  ppp0 -p udp --dport 500 -j ACCEPT
# iptables --append INPUT --in-interface  ppp0 -p udp --dport 4500 -j ACCEPT
# iptables --append INPUT --in-interface  ppp0 -p 50 -j ACCEPT
</screen>
        </para>

        <para>
          If you haven't setup your Linux box as a gateway yet then
          you have to allow forwarding/masqing for the boxes on
          the LAN (and therefore for the VPN clients):
<screen>
# iptables --table nat --append POSTROUTING --out-interface ppp0 -j MASQUERADE
# iptables --append FORWARD --in-interface eth0 -j ACCEPT
# echo 1 > /proc/sys/net/ipv4/ip_forward
</screen>
        </para>
      </sect3>
    </sect2>
  </sect1>

  <sect1 id="references">
    <title>References</title>
    <variablelist>
      <varlistentry>
        <term>VPN Reference</term>
        <listitem>
          <para>
            <ulink url="http://www.jacco2.dds.nl/networking/freeswan-l2tp.html"></ulink>
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>L2TPns Project</term>
        <listitem>
          <para><ulink url="http://l2tpns.sourceforge.net"></ulink></para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>OpenSWAN Project</term>
        <listitem>
          <para><ulink url="http://www.openswan.org"></ulink></para>
        </listitem>
      </varlistentry>
    </variablelist>
  </sect1>
</article>