Tom Eastep 2005-04-13 2001 2002 2003 2004 2005 Thomas M. Eastep 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 GNU Free Documentation License. 1.4 2004-11-02 TE Added link to Greg Kops's tutorial. 1.3 2004-05-22 TE Warning about PPTP conntrack patch and GRE tunnels. 1.2 2004-04-15 TE Revised instructions regarding PPTP conntrack patch. 1.1 2003-12-23 TE Added note about PPTP module support in Bering 1.2 Shorewall easily supports PPTP in a number of configurations.

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. The Linux PPTP client project 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 PPTP Server running behind your Firewall below). http://pptpclient.sourceforge.net Everything you need to run a PPTP client. http://www.poptop.org The kernelmod package can be used to quickly install MPPE into your kernel without rebooting. http://devel.elucid8design.com/el8/devel/tutorials/pptp.php A nice tutorial for installing a PPTP server on Fedora. 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 roll their own.

I recommend reading the VPN Basics article if you plan to implement any type of VPN.

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. The steps involved are:

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 ftp://ftp.samba.org/pub/ppp. You will need the following patches: 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-MSCHAPv2-fix.patch.gz You may also want the following patch if you want to require remote hosts to use encryption: ftp://ftp.shorewall.net/pub/shorewall/pptp/require-mppe.diff 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): cd ppp-2.4.1 patch -p1 < ../ppp-2.4.0-openssl-0.9.6-mppe.patch patch -p1 < ../ppp-2.4.1-MSCHAPv2-fix.patch (Optional) patch -p1 < ../require-mppe.diff ./configure make You will need to install the resulting binary on your firewall system. To do that, I NFS mount my source filesystem and use make install from the ppp-2.4.1 directory.

You will need one of the following patches depending on your kernel version: http://www.shorewall.net/pub/shorewall/pptp/linux-2.4.4-openssl-0.9.6a-mppe-patch.gz http://www.shorewall/net/pub/shorewall/pptp/linux-2.4.16-openssl-0.9.6b-mppe-patch.gz Uncompress the patch into the same directory where your top-level kernel source is located and: cd <your GNU/Linux source top-level directory> patch -p1 < ../linux-2.4.16-openssl-0.9.6b-mppe.patch Now configure your kernel. Here is my ppp configuration:

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: [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

Here is a copy of my /etc/ppp/options.poptop file: 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 System 192.168.1.3 acts as a WINS server so I have included that IP as the ms-wins value. I have pointed the remote clients at my DNS server -- it has external address 206.124.146.177. I am requiring 128-bit stateless compression (my kernel is built with the require-mppe.diff patch mentioned above. Here's my /etc/ppp/chap-secrets: Secrets for authentication using CHAP # client server secret IP addresses CPQTDM\\TEastep * <shhhhhh> 192.168.1.7 TEastep * <shhhhhh> 192.168.1.7 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. You will also want the following in /etc/modules.conf: alias ppp-compress-18 ppp_mppe alias ppp-compress-21 bsd_comp alias ppp-compress-24 ppp_deflate alias ppp-compress-26 ppp_deflate

PoPTop (pptpd) is available from http://www.poptop.org/. Here is a copy of my /etc/pptpd.conf file: option /etc/ppp/options.poptop speed 115200 localip 192.168.1.254 remoteip 192.168.1.33-38 I specify the /etc/ppp/options.poptop file as my ppp options file (I have several). The local IP is the same as my internal interface's (192.168.1.254). I have assigned a remote IP range that overlaps my local network. This, together with proxyarp in my /etc/ppp/options.poptop file make the remote hosts look like they are part of the local subnetwork. I use this file to start/stop pptpd -- I have this in /etc/init.d/pptpd: #!/bin/sh # # /etc/rc.d/init.d/pptpd # # chkconfig: 5 12 85 # description: control pptp server # case "$1" in start) echo 1 > /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

Here' a basic setup that treats your remote users as if they were part of your loc zone. Note that if your primary internet connection uses ppp0, then be sure that loc follows net in /etc/shorewall/zones. /etc/shorewall/tunnels: #TYPE ZONE GATEWAY GATEWAY ZONE pptpserver net 0.0.0.0/0 /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS loc ppp+

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 vpn follows net in /etc/shorewall/zones as shown below. /etc/shorewall/tunnels: #TYPE ZONE GATEWAY GATEWAY ZONE pptpserver net 0.0.0.0/0 /etc/shorewall/zones: #ZONE DISPLAY COMMENTS net Internet The Internet loc Local Local Network vpn VPN Remote Users /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS net eth0 206.124.146.255 norfc1918 loc eth2 192.168.10.255 vpn ppp+ Your policies and rules may now be configured for traffic to/from the vpn zone.

Often there will be situations where you want multiple connections from remote networks with these networks having different firewalling requirements. Here's how you configure this in Shorewall. Note that if your primary internet connection uses ppp0 then be sure that the vpn{1-3} zones follows net in /etc/shorewall/zones as shown below. /etc/shorewall/tunnels: #TYPE ZONE GATEWAY GATEWAY ZONE pptpserver net 0.0.0.0/0 /etc/shorewall/zones: #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 /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS net eth0 206.124.146.255 norfc1918 loc eth2 192.168.10.255 - ppp+ /etc/shorewall/hosts: #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 Your policies and rules can now be configured using separate zones (vpn1, vpn2, and vpn3) for the three remote network.

If you have a single external IP address, add the following to your /etc/shorewall/rules file: /etc/shorewall/rules: #ACTION SOURCE DEST PROTO DEST PORT(S) DNAT net loc:<server address> tcp 1723 DNAT net loc:<server address> 47 If you have multiple external IP address and you want to forward a single <external address>, add the following to your /etc/shorewall/rules file: /etc/shorewall/rules: #ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST DNAT net loc:<server address> tcp 1723 - <external address> DNAT net loc:<server address> 47 - - <external address>

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 Netfilter Patch-O-Matic (some distributions are now shipping with this patch installed). I recommend that you also add these four lines to your /etc/shorewall/modules file: loadmodule ip_conntrack_proto_gre loadmodule ip_conntrack_pptp loadmodule ip_nat_pptp loadmodule ip_nat_proto_gre 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. Installing the above modules will prevent any GRE tunnels that you have from working correctly.

The PPTP GNU/Linux client is available at http://sourceforge.net/projects/pptpclient/. Rather than use the configuration script that comes with the client, I built my own. I also build my own kernel as described above 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). The key elements of this setup are as follows: Define a zone for the remote network accessed via PPTP. Associate that zone with a ppp interface. Define rules for PPTP traffic to/from the firewall. Define rules for traffic two and from the remote zone. Here are examples from one of my old setups: /etc/shorewall/zones: #ZONE DISPLAY COMMENTS cpq Compaq Compaq Intranet /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS - ppp+ /etc/shorewall/hosts: #ZONE HOST(S) OPTIONS cpq ppp+:!192.168.1.0/24 /etc/shorewall/tunnels: #TYPE ZONE GATEWAY GATEWAY ZONE pptpclient net 0.0.0.0/0 I use the combination of interface and hosts file to define the cpq 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. 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 :-( #!/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 > /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> /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 > /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 Here's my /etc/ppp/options file: # # 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 My /etc/ppp/ip-up.local file sets up the routes that I need to route Compaq traffic through the PPTP tunnel: #/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 Finally, I run the following script every five minutes under crond to restart the tunnel if it fails: #!/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 > /dev/null 2>&1 & Here's a script and corresponding ip-up.local from Jerry Vonau jvonau@home.com that controls two PPTP connections.

Some ADSL systems in Europe (most notably in Austria) feature a PPTP server built into an ADSL Modem. In this setup, an ethernet interface is dedicated to supporting the PPTP tunnel between the firewall and the Modem 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. These changes are in addition to those described in the QuickStart Guides. Lets assume the following: ADSL Modem connected through eth0 Modem IP address = 192.168.1.1 eth0 IP address = 192.168.1.2 The changes you need to make are as follows: Add this entry to /etc/shorewall/zones: #ZONE DISPLAY COMMENTS modem Modem ADSL Modem That entry defines a new zone called modem which will contain only your ADSL modem. Add the following entry to /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS modem eth0 192.168.1.255 dhcp You will of course modify the net entry in /etc/shorewall/interfaces to specify ppp0 as the interface as described in the QuickStart Guide corresponding to your setup. Add the following to /etc/shorewall/tunnels: #TYPE ZONE GATEWAY GATEWAY ZONE pptpclient modem 192.168.1.1 That entry allows a PPTP tunnel to be established between your Shorewall system and the PPTP server in the modem.