shorewall_code/docs/PPTP.xml

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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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<article id="PPTP">
  <!--$Id$-->

  <articleinfo>
    <title>PPTP - Unmaintained</title>

    <authorgroup>
      <author>
        <firstname>Tom</firstname>

        <surname>Eastep</surname>
      </author>
    </authorgroup>

    <pubdate><?dbtimestamp format="Y/m/d"?></pubdate>

    <copyright>
      <year>2001</year>

      <year>2002</year>

      <year>2003</year>

      <year>2004</year>

      <year>2005</year>

      <year>2006</year>

      <holder>Thomas M. Eastep</holder>
    </copyright>

    <legalnotice>
      <para>Permission is granted to copy, distribute and/or modify this
      document under the terms of the GNU Free Documentation License, Version
      1.2 or any later version published by the Free Software Foundation; with
      no Invariant Sections, with no Front-Cover, and with no Back-Cover
      Texts. A copy of the license is included in the section entitled
      <quote><ulink url="GnuCopyright.htm">GNU Free Documentation
      License</ulink></quote>.</para>
    </legalnotice>

    <revhistory>
      <revision>
        <revnumber>1.4</revnumber>

        <date>2004-11-02</date>

        <authorinitials>TE</authorinitials>

        <revremark>Added link to Greg Kops's tutorial.</revremark>
      </revision>

      <revision>
        <revnumber>1.3</revnumber>

        <date>2004-05-22</date>

        <authorinitials>TE</authorinitials>

        <revremark>Warning about PPTP conntrack patch and GRE
        tunnels.</revremark>
      </revision>

      <revision>
        <revnumber>1.2</revnumber>

        <date>2004-04-15</date>

        <authorinitials>TE</authorinitials>

        <revremark>Revised instructions regarding PPTP conntrack
        patch.</revremark>
      </revision>

      <revision>
        <revnumber>1.1</revnumber>

        <date>2003-12-23</date>

        <authorinitials>TE</authorinitials>

        <revremark>Added note about PPTP module support in Bering
        1.2</revremark>
      </revision>
    </revhistory>

    <abstract>
      <para>Shorewall easily supports PPTP in a number of
      configurations.</para>
    </abstract>
  </articleinfo>

  <warning>
    <para><emphasis role="bold">This document is no longer maintained. Any
    volunteers?</emphasis></para>
  </warning>

  <section>
    <title>Overview</title>

    <note>
      <para>I am no longer attempting to maintain MPPE patches for current
      Linux kernel's and pppd. I recommend that you refer to the following
      URLs for information about installing MPPE into your kernel and
      pppd.</para>
    </note>

    <para>The <ulink url="http://pptpclient.sourceforge.net">Linux PPTP client
    project</ulink> has a nice GUI for configuring and managing VPN
    connections where your Linux system is the PPTP client. This is what I
    currently use. I am no longer running PoPToP but rather I use the PPTP
    Server included with XP Professional (see <ulink
    url="PPTP.htm#ServerBehind">PPTP Server running behind your
    Firewall</ulink> below).</para>

    <variablelist>
      <varlistentry>
        <term><ulink
        url="http://pptpclient.sourceforge.net">http://pptpclient.sourceforge.net</ulink></term>

        <listitem>
          <para>Everything you need to run a PPTP client.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><ulink
        url="http://www.poptop.org">http://www.poptop.org</ulink></term>

        <listitem>
          <para>The <quote>kernelmod</quote> package can be used to quickly
          install MPPE into your kernel without rebooting.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><ulink
        url="http://devel.elucid8design.com/el8/devel/tutorials/pptp.php">http://devel.elucid8design.com/el8/devel/tutorials/pptp.php</ulink></term>

        <listitem>
          <para>A nice tutorial for installing a PPTP server on Fedora.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>I am leaving the instructions for building MPPE-enabled kernels and
    pppd in the text below for those who may wish to obtain the relevant
    current patches and <quote>roll their own</quote>.</para>
  </section>

  <section>
    <title>Preliminary Reading</title>

    <para>I recommend reading the <ulink url="VPNBasics.html">VPN
    Basics</ulink> article if you plan to implement any type of VPN.</para>
  </section>

  <section id="ServerFW">
    <title>PPTP Server Running on your Firewall</title>

    <para>I will try to give you an idea of how to set up a PPTP server on
    your firewall system. This isn't a detailed HOWTO but rather an example of
    how I have set up a working PPTP server on my own firewall.</para>

    <para>The steps involved are:</para>

    <orderedlist>
      <listitem>
        <para><xref linkend="PatchPppd" /></para>
      </listitem>

      <listitem>
        <para><xref linkend="PatchKernel" /></para>
      </listitem>

      <listitem>
        <para><xref linkend="Samba" /></para>
      </listitem>

      <listitem>
        <para><xref linkend="ConfigPppd" /></para>
      </listitem>

      <listitem>
        <para><xref linkend="ConfigPptpd" /></para>
      </listitem>

      <listitem>
        <para><xref linkend="ConfigFw" /></para>
      </listitem>
    </orderedlist>

    <section id="PatchPppd">
      <title>Patching and building pppd</title>

      <para>To run pppd on a 2.4 kernel, you need the pppd 2.4.1 or later. The
      primary site for releases of pppd is <ulink
      url="ftp://ftp.samba.org/pub/ppp">ftp://ftp.samba.org/pub/ppp</ulink>.</para>

      <para>You will need the following patches:</para>

      <simplelist>
        <member><ulink
        url="http://www.shorewall.net/pub/shorewall/pptp/ppp-2.4.1-openssl-0.9.6-mppe-patch.gz">http://www.shorewall.net/pub/shorewall/pptp/ppp-2.4.1-openssl-0.9.6-mppe-patch.gz</ulink></member>

        <member><ulink
        url="http://www.shorewall.net/pub/shorewall/pptp/ppp-2.4.1-MSCHAPv2-fix.patch.gz">http://www.shorewall.net/pub/shorewall/pptp/ppp-2.4.1-MSCHAPv2-fix.patch.gz</ulink></member>
      </simplelist>

      <para>You may also want the following patch if you want to require
      remote hosts to use encryption:</para>

      <simplelist>
        <member><ulink
        url="ftp://ftp.shorewall.net/pub/shorewall/pptp/require-mppe.diff">ftp://ftp.shorewall.net/pub/shorewall/pptp/require-mppe.diff</ulink></member>
      </simplelist>

      <para>Un-tar the pppd source and uncompress the patches into one
      directory (the patches and the ppp-2.4.1 directory are all in a single
      parent directory):</para>

      <programlisting>cd ppp-2.4.1
patch -p1 &lt; ../ppp-2.4.0-openssl-0.9.6-mppe.patch
patch -p1 &lt; ../ppp-2.4.1-MSCHAPv2-fix.patch
(Optional) patch -p1 &lt; ../require-mppe.diff
./configure
make</programlisting>

      <para>You will need to install the resulting binary on your firewall
      system. To do that, I NFS mount my source filesystem and use <quote>make
      install</quote> from the ppp-2.4.1 directory.</para>
    </section>

    <section id="PatchKernel">
      <title>Patching and building your Kernel</title>

      <para>You will need one of the following patches depending on your
      kernel version:</para>

      <simplelist>
        <member>http://www.shorewall.net/pub/shorewall/pptp/linux-2.4.4-openssl-0.9.6a-mppe-patch.gz</member>

        <member>http://www.shorewall/net/pub/shorewall/pptp/linux-2.4.16-openssl-0.9.6b-mppe-patch.gz</member>
      </simplelist>

      <para>Uncompress the patch into the same directory where your top-level
      kernel source is located and:</para>

      <programlisting>cd &lt;your GNU/Linux source top-level directory&gt;
patch -p1 &lt; ../linux-2.4.16-openssl-0.9.6b-mppe.patch</programlisting>

      <para>Now configure your kernel. Here is my ppp configuration:</para>

      <graphic fileref="images/ppp.jpg" />
    </section>

    <section id="Samba">
      <title>Configuring Samba</title>

      <para>You will need a WINS server (Samba configured to run as a WINS
      server is fine). Global section from /etc/samba/smb.conf on my WINS
      server (192.168.1.3) is:</para>

      <programlisting>[global]
     workgroup = TDM-NSTOP
     netbios name = WOOKIE
     server string = GNU/Linux Box
     encrypt passwords = Yes
     log file = /var/log/samba/%m.log
     max log size = 0
     socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
     os level = 65
     domain master = True
     preferred master = True
     dns proxy = No
     wins support = Yes
     printing = lprng

[homes]
     comment = Home Directories
     valid users = %S
     read only = No
     create mask = 0664
     directory mask = 0775

[printers]
     comment = All Printers
     path = /var/spool/samba
     printable = Yes</programlisting>
    </section>

    <section id="ConfigPppd">
      <title>Configuring pppd</title>

      <para>Here is a copy of my /etc/ppp/options.poptop file:</para>

      <programlisting>ipparam PoPToP
lock
mtu 1490
mru 1490
ms-wins 192.168.1.3
ms-dns 206.124.146.177
multilink
proxyarp
auth
+chap
+chapms
+chapms-v2
ipcp-accept-local
ipcp-accept-remote
lcp-echo-failure 30
lcp-echo-interval 5
deflate 0
mppe-128
mppe-stateless
require-mppe
require-mppe-stateless</programlisting>

      <note>
        <itemizedlist>
          <listitem>
            <para>System 192.168.1.3 acts as a WINS server so I have included
            that IP as the <quote>ms-wins</quote> value.</para>
          </listitem>

          <listitem>
            <para>I have pointed the remote clients at my DNS server -- it has
            external address 206.124.146.177.</para>
          </listitem>

          <listitem>
            <para>I am requiring 128-bit stateless compression (my kernel is
            built with the <quote>require-mppe.diff</quote> patch mentioned
            above.</para>
          </listitem>
        </itemizedlist>
      </note>

      <para>Here's my /etc/ppp/chap-secrets:</para>

      <programlisting>Secrets for authentication using CHAP
# client        server    secret    IP addresses
CPQTDM\\TEastep *         &lt;shhhhhh&gt; 192.168.1.7
TEastep         *         &lt;shhhhhh&gt; 192.168.1.7</programlisting>

      <para>I am the only user who connects to the server but I may connect
      either with or without a domain being specified. The system I connect
      from is my laptop so I give it the same IP address when tunneled in at
      it has when I use its wireless LAN card around the house.</para>

      <para>You will also want the following in /etc/modules.conf:</para>

      <programlisting>alias ppp-compress-18 ppp_mppe
alias ppp-compress-21 bsd_comp
alias ppp-compress-24 ppp_deflate
alias ppp-compress-26 ppp_deflate</programlisting>
    </section>

    <section id="ConfigPptpd">
      <title>Configuring pptpd</title>

      <para>PoPTop (pptpd) is available from <ulink
      url="http://www.poptop.org/">http://www.poptop.org/</ulink>.</para>

      <para>Here is a copy of my /etc/pptpd.conf file:</para>

      <programlisting>option /etc/ppp/options.poptop
speed 115200
localip 192.168.1.254
remoteip 192.168.1.33-38</programlisting>

      <note>
        <itemizedlist>
          <listitem>
            <para>I specify the /etc/ppp/options.poptop file as my ppp options
            file (I have several).</para>
          </listitem>

          <listitem>
            <para>The local IP is the same as my internal interface's
            (192.168.1.254).</para>
          </listitem>

          <listitem>
            <para>I have assigned a remote IP range that overlaps my local
            network. This, together with <quote>proxyarp</quote> in my
            /etc/ppp/options.poptop file make the remote hosts look like they
            are part of the local subnetwork.</para>
          </listitem>
        </itemizedlist>
      </note>

      <para>I use this file to start/stop pptpd -- I have this in
      /etc/init.d/pptpd:</para>

      <programlisting>#!/bin/sh
#
# /etc/rc.d/init.d/pptpd
#
# chkconfig: 5 12 85
# description: control pptp server
#

case "$1" in
start)
    echo 1 &gt; /proc/sys/net/ipv4/ip_forward
    modprobe ppp_async
    modprobe ppp_generic
    modprobe ppp_mppe
    modprobe slhc
    if /usr/local/sbin/pptpd; then
        touch /var/lock/subsys/pptpd
    fi
    ;;
stop)
    killall pptpd
    rm -f /var/lock/subsys/pptpd
    ;;
restart)
    killall pptpd
    if /usr/local/sbin/pptpd; then
        touch /var/lock/subsys/pptpd
    fi
    ;;
status)
    ifconfig
    ;;
*)
    echo "Usage: $0 {start|stop|restart|status}"
    ;;
esac</programlisting>
    </section>

    <section id="ConfigFw">
      <title>Configuring Shorewall</title>

      <section>
        <title>Basic Setup</title>

        <para>Here' a basic setup that treats your remote users as if they
        were part of your <emphasis role="bold">loc</emphasis> zone. Note that
        if your primary internet connection uses ppp0, then be sure that
        <emphasis role="bold">loc</emphasis> follows <emphasis
        role="bold">net</emphasis> in /etc/shorewall/zones.</para>

        <para><filename>/etc/shorewall/tunnels</filename>:</para>

        <programlisting>#TYPE           ZONE             GATEWAY           GATEWAY ZONE
pptpserver      net              0.0.0.0/0</programlisting>

        <para><filename>/etc/shorewall/interfaces</filename>:</para>

        <programlisting>#ZONE          INTERFACE         BROADCAST        OPTIONS
loc            ppp+</programlisting>
      </section>

      <section>
        <title>Remote Users in a Separate Zone</title>

        <para>If you want to place your remote users in their own zone so that
        you can control connections between these users and the local network,
        follow this example. Note that if your primary internet connection
        uses ppp0 then be sure that <emphasis role="bold">vpn</emphasis>
        follows <emphasis role="bold">net</emphasis> in /etc/shorewall/zones
        as shown below.</para>

        <para><filename>/etc/shorewall/tunnels</filename>:</para>

        <programlisting>#TYPE           ZONE             GATEWAY           GATEWAY ZONE
pptpserver      net              0.0.0.0/0</programlisting>

        <para><filename>/etc/shorewall/zones</filename>:</para>

        <programlisting>#ZONE           DISPLAY          COMMENTS
net             Internet         The Internet
loc             Local            Local Network
vpn             VPN              Remote Users</programlisting>

        <para><filename>/etc/shorewall/interfaces</filename>:</para>

        <programlisting>#ZONE          INTERFACE         BROADCAST        OPTIONS
net            eth0              206.124.146.255  norfc1918
loc            eth2              192.168.10.255
vpn            ppp+</programlisting>

        <para>Your policies and rules may now be configured for traffic
        to/from the <emphasis role="bold">vpn</emphasis> zone.</para>
      </section>

      <section>
        <title>Multiple Remote Networks</title>

        <para>Often there will be situations where you want multiple
        connections from remote networks with these networks having different
        firewalling requirements.<graphic
        fileref="images/MultiPPTP.png" /></para>

        <para>Here's how you configure this in Shorewall. Note that if your
        primary internet connection uses ppp0 then be sure that the <emphasis
        role="bold">vpn{1-3}</emphasis> zones follows <emphasis
        role="bold">net</emphasis> in /etc/shorewall/zones as shown
        below.</para>

        <para><filename>/etc/shorewall/tunnels</filename>:</para>

        <programlisting>#TYPE           ZONE             GATEWAY           GATEWAY ZONE
pptpserver      net              0.0.0.0/0</programlisting>

        <para><filename>/etc/shorewall/zones</filename>:</para>

        <programlisting>#ZONE           DISPLAY          COMMENTS
net             Internet         The Internet
loc             Local            Local Network
vpn1            Remote1          Remote Network 1
vpn2            Remote2          Remote Network 2
vpn3            Remote3          Remote Network 3</programlisting>

        <para><filename>/etc/shorewall/interfaces</filename>:</para>

        <programlisting>#ZONE          INTERFACE         BROADCAST        OPTIONS
net            eth0              206.124.146.255  norfc1918
loc            eth2              192.168.10.255
-              ppp+</programlisting>

        <para><filename>/etc/shorewall/hosts</filename>:</para>

        <programlisting>#ZONE          HOST(S)                   OPTIONS
vpn1           ppp+:192.168.1.0/24
vpn2           ppp+:192.168.2.0/24
vpn3           ppp+:192.168.3.0/24</programlisting>

        <para>Your policies and rules can now be configured using separate
        zones (vpn1, vpn2, and vpn3) for the three remote network.</para>
      </section>
    </section>
  </section>

  <section id="ServerBehind">
    <title>PPTP Server Running Behind your Firewall</title>

    <para>If you have a single external IP address, add the following to your
    /etc/shorewall/rules file:</para>

    <para><filename>/etc/shorewall/rules</filename>:</para>

    <programlisting>#ACTION      SOURCE         DEST                  PROTO       DEST PORT(S)
DNAT         net            loc:<emphasis>&lt;server address&gt;</emphasis>  tcp         1723
DNAT         net            loc:<emphasis>&lt;server address&gt;</emphasis>  47</programlisting>

    <para>If you have multiple external IP address and you want to forward a
    single &lt;<emphasis>external address</emphasis>&gt;, add the following to
    your /etc/shorewall/rules file:</para>

    <para><filename>/etc/shorewall/rules</filename>:</para>

    <programlisting>#ACTION      SOURCE         DEST                  PROTO       DEST PORT(S)     SOURCE          ORIGINAL
#                                                                              PORT(S)         DEST
DNAT         net            loc:<emphasis>&lt;server address&gt;</emphasis>  tcp         1723             -               <emphasis>&lt;external address&gt;</emphasis>
DNAT         net            loc:<emphasis>&lt;server address&gt;</emphasis>  47          -                -               <emphasis>&lt;external address&gt;</emphasis></programlisting>
  </section>

  <section id="ClientsBehind">
    <title>PPTP Clients Running Behind your Firewall</title>

    <para>You shouldn't have to take any special action for this case unless
    you wish to connect multiple clients to the same external server. In that
    case, you must install the PPTP connection/tracking and NAT patch from
    <ulink url="http://www.netfilter.org">Netfilter Patch-O-Mati</ulink>c
    (some distributions are now shipping with this patch installed). I
    recommend that you also add these four lines to your
    /etc/shorewall/modules file:</para>

    <programlisting>loadmodule ip_conntrack_proto_gre
loadmodule ip_conntrack_pptp
loadmodule ip_nat_pptp
loadmodule ip_nat_proto_gre</programlisting>

    <para>For LEAF/Bering users, the 2.4.20 kernel as already been patched as
    described at the URL above and the three modules are included in the
    Bering 1.2 modules tarball.</para>

    <warning>
      <para>Installing the above modules will prevent any GRE tunnels that you
      have from working correctly.</para>
    </warning>
  </section>

  <section id="ClientFW">
    <title>PPTP Client Running on your Firewall</title>

    <para>The PPTP GNU/Linux client is available at <ulink
    url="http://sourceforge.net/projects/pptpclient/">http://sourceforge.net/projects/pptpclient/</ulink>.
    Rather than use the configuration script that comes with the client, I
    built my own. I also build my own kernel <link linkend="PatchKernel">as
    described above</link> rather than using the mppe package that is
    available with the client. My /etc/ppp/options file is mostly unchanged
    from what came with the client (see below).</para>

    <para>The key elements of this setup are as follows:</para>

    <orderedlist>
      <listitem>
        <para>Define a zone for the remote network accessed via PPTP.</para>
      </listitem>

      <listitem>
        <para>Associate that zone with a ppp interface.</para>
      </listitem>

      <listitem>
        <para>Define rules for PPTP traffic to/from the firewall.</para>
      </listitem>

      <listitem>
        <para>Define rules for traffic two and from the remote zone.</para>
      </listitem>
    </orderedlist>

    <para>Here are examples from one of my old setups:</para>

    <para><filename>/etc/shorewall/zones</filename>:</para>

    <programlisting>#ZONE          DISPLAY          COMMENTS
cpq            Compaq           Compaq Intranet</programlisting>

    <para><filename>/etc/shorewall/interfaces</filename>:</para>

    <programlisting>#ZONE          INTERFACE        BROADCAST          OPTIONS
-              ppp+</programlisting>

    <para>/etc/shorewall/hosts:</para>

    <programlisting>#ZONE          HOST(S)                             OPTIONS
cpq            ppp+:!192.168.1.0/24</programlisting>

    <para><filename>/etc/shorewall/tunnels</filename>:</para>

    <programlisting>#TYPE          ZONE             GATEWAY            GATEWAY ZONE
pptpclient     net              0.0.0.0/0</programlisting>

    <para>I use the combination of interface and hosts file to define the
    <quote>cpq</quote> zone because I also run a PPTP server on my firewall
    (see above). Using this technique allows me to distinguish clients of my
    own PPTP server from arbitrary hosts at Compaq; I assign addresses in
    192.168.1.0/24 to my PPTP clients and Compaq doesn't use that RFC1918
    Class C subnet.</para>

    <para>I use this script in /etc/init.d to control the client. The reason
    that I disable ECN when connecting is that the Compaq tunnel servers don't
    do ECN yet and reject the initial TCP connection request if I enable ECN
    :-(</para>

    <programlisting>#!/bin/sh
#
# /etc/rc.d/init.d/pptp
#
# chkconfig: 5 60 85
# description: PPTP Link Control
#
NAME="Tandem"
ADDRESS=tunnel-tandem.compaq.com
USER='Tandem\tommy'
ECN=0
DEBUG=

start_pptp() {
    echo $ECN &gt; /proc/sys/net/ipv4/tcp_ecn
    if /usr/sbin/pptp $ADDRESS user $USER noauth $DEBUG; then
        touch /var/lock/subsys/pptp
        echo "PPTP Connection to $NAME Started"
    fi
}

stop_pptp() {
    if killall /usr/sbin/pptp 2&gt; /dev/null; then
        echo "Stopped pptp"
    else
        rm -f /var/run/pptp/*
    fi

    # if killall pppd; then
    # echo "Stopped pppd"
    # fi

    rm -f /var/lock/subsys/pptp

    echo 1 &gt; /proc/sys/net/ipv4/tcp_ecn
}


case "$1" in
start)
    echo "Starting PPTP Connection to ${NAME}..."
    start_pptp
    ;;
stop)
    echo "Stopping $NAME PPTP Connection..."
    stop_pptp
    ;;
restart)
    echo "Restarting $NAME PPTP Connection..."
    stop_pptp
    start_pptp
    ;;
status)
    ifconfig
    ;;
*)
    echo "Usage: $0 {start|stop|restart|status}"
    ;;
esac</programlisting>

    <para>Here's my /etc/ppp/options file:</para>

    <programlisting>#
# Identify this connection
#
ipparam Compaq
#
# Lock the port
#
lock
#
# We don't need the tunnel server to authenticate itself
#
noauth

+chap
+chapms
+chapms-v2

multilink
mrru 1614
#
# Turn off transmission protocols we know won't be used
#
nobsdcomp
nodeflate

#
# We want MPPE
#
mppe-128
mppe-stateless

#
# We want a sane mtu/mru
#
mtu 1000
mru 1000

#
# Time this thing out of it goes poof
#
lcp-echo-failure 10
lcp-echo-interval 10</programlisting>

    <para>My /etc/ppp/ip-up.local file sets up the routes that I need to route
    Compaq traffic through the PPTP tunnel:</para>

    <programlisting>#/bin/sh

case $6 in
Compaq)
    route add -net 16.0.0.0 netmask 255.0.0.0 gw $5 $1
    route add -net 130.252.0.0 netmask 255.255.0.0 gw $5 $1
    route add -net 131.124.0.0 netmask 255.255.0.0 gw $5 $1
    ...
    ;;
esac</programlisting>

    <para>Finally, I run the following script every five minutes under crond
    to restart the tunnel if it fails:</para>

    <programlisting>#!/bin/sh
restart_pptp() {
    /sbin/service pptp stop
    sleep 10
    if /sbin/service pptp start; then
        /usr/bin/logger "PPTP Restarted"
    fi
}

if [ -n "`ps ax | grep /usr/sbin/pptp | grep -v grep`" ]; then
    exit 0
fi

echo "Attempting to restart PPTP"

restart_pptp &gt; /dev/null 2&gt;&amp;1 &amp;</programlisting>

    <para><ulink url="ftp://ftp.shorewall.net/pub/shorewall/misc/Vonau">Here's
    a script and corresponding ip-up.local</ulink> from Jerry Vonau
    <email>jvonau@home.com</email> that controls two PPTP connections.</para>
  </section>

  <section id="PPTP_ADSL">
    <title>PPTP Client running on your Firewall with PPTP Server in an ADSL
    Modem</title>

    <para>Some ADSL systems in Europe (most notably in Austria and the Netherlands) feature a PPTP
    server built into an ADSL <quote>Modem</quote>. In this setup, an ethernet
    interface is dedicated to supporting the PPTP tunnel between the firewall
    and the <quote>Modem</quote> while the actual internet access is through
    PPTP (interface ppp0). If you have this type of setup, you need to modify
    the sample configuration that you downloaded as described in this section.
    <emphasis role="bold">These changes are in addition to those described in
    the <ulink url="shorewall_quickstart_guide.htm">QuickStart
    Guides</ulink>.</emphasis></para>

    <para>Lets assume the following:</para>

    <itemizedlist>
      <listitem>
        <para>ADSL Modem connected through eth0</para>
      </listitem>

      <listitem>
        <para>Modem IP address = 192.168.1.1</para>
      </listitem>

      <listitem>
        <para>eth0 IP address = 192.168.1.2</para>
      </listitem>
    </itemizedlist>

    <para>The changes you need to make are as follows:</para>

    <orderedlist>
      <listitem>
        <para>Add this entry to /etc/shorewall/zones:</para>

        <programlisting>#ZONE          DISPLAY          COMMENTS
modem          Modem            ADSL Modem</programlisting>

        <para>That entry defines a new zone called <quote>modem</quote> which
        will contain only your ADSL modem.</para>
      </listitem>

      <listitem>
        <para>Add the following entry to /etc/shorewall/interfaces:</para>

        <programlisting>#ZONE          INTERFACE        BROADCAST          OPTIONS
modem          eth0             192.168.1.255      dhcp</programlisting>

        <para>You will of course modify the <quote>net</quote> entry in
        /etc/shorewall/interfaces to specify <quote>ppp0</quote> as the
        interface as described in the QuickStart Guide corresponding to your
        setup.</para>
      </listitem>

      <listitem>
        <para>Add the following to /etc/shorewall/tunnels:</para>

        <programlisting>#TYPE          ZONE             GATEWAY            GATEWAY ZONE
pptpclient     modem            192.168.1.1</programlisting>

        <para>That entry allows a PPTP tunnel to be established between your
        Shorewall system and the PPTP server in the modem.</para>
      </listitem>
    </orderedlist>
  </section>
</article>