PPTP Client

Related articles

• PPTP server

pptpclient is a program implementing the Microsoft PPTP protocol. As such, it can be used to connect to a Microsoft VPN network (or any PPTP-based VPN) provided by a school or workplace.

Warning: The PPTP protocol is inherently insecure. See http://poptop.sourceforge.net/dox/protocol-security.phtml for details.

Installation

Install the pptpclient package.

Configure

To configure pptpclient you will need to collect the following information from your network administrator:

• The IP address or hostname of the VPN server.
• The username you will use to connect.
• The password you will use to connect.
• The authentication (Windows) domain name. This is not necessary for certain networks.

You must also decide what to name the tunnel.

Configure using pptpsetup

You can configure and delete tunnels by running the pptpsetup tool as root. For example:

pptpsetup --create my_tunnel --server vpn.example.com --username alice --password foo --encrypt
pptpsetup --delete my_tunnel

You can #Connect after a tunnel has been configured.

Configure by hand

You can also edit all necessary configuration files by hand, rather than relying on pptpsetup.

Edit The options File

The /etc/ppp/options file sets security options for your VPN client. If you have trouble connecting to your network, you may need to relax the options. At a minimum, this file should contain the options lock, noauth, nobsdcomp and nodeflate.

/etc/ppp/options

# Lock the port
lock
# We don't need the tunnel server to authenticate itself
noauth
# Turn off compression protocols we know won't be used
nobsdcomp
nodeflate
# We won't do PAP, EAP, CHAP, or MSCHAP, but we will accept MSCHAP-V2
# (you may need to remove these refusals if the server is not using MPPE)
refuse-pap
refuse-eap
refuse-chap
refuse-mschap

Edit The chap-secrets File

The /etc/ppp/chap-secrets file contains credentials for authenticating a tunnel. Make sure no one except root can read this file, as it contains sensitive information.

chmod 0600 /etc/ppp/chap-secrets

Edit the file. It has the following format:

/etc/ppp/chap-secrets

<DOMAIN>\\<USERNAME> PPTP <PASSWORD> *

Replace each bracketed term with an appropriate value. Omit <DOMAIN>\\ if your connection does not require a domain.

Note: Place your password in double quotation marks (") if it contains special characters such as $.

Warning: This file contains passwords in plain text. Guard it well!

Name Your Tunnel

The /etc/ppp/peers/<TUNNEL> file contains tunnel-specific configuration options. <TUNNEL> is the name you wish to use for your VPN connection. The file should look like this:

/etc/ppp/peers/<TUNNEL>

pty "pptp <SERVER> --nolaunchpppd"
name <DOMAIN>\\<USERNAME>
remotename PPTP
require-mppe-128
file /etc/ppp/options
ipparam <TUNNEL>

Again, omit <DOMAIN>\\ if your connection does not require a domain. <SERVER> is the remote address of the VPN server, <DOMAIN> is the domain your user belongs to, <USERNAME> is the name you will use to connect to the server, and <TUNNEL> is the name of the connection.

Note: remotename PPTP is used to find <PASSWORD> in the /etc/ppp/chap-secrets File.

Note: If you do not need MPPE support, you should remove the require-mppe-128 option from this file and from /etc/ppp/options

Connect

To make sure that everything is configured properly, as root execute:

# pon <TUNNEL> debug dump logfd 2 nodetach

If everything has been configured correctly, the pon command should not terminate. Once you are satisfied that it has connected successfully, you can terminate the command.

Note: As an additional verification you can run ip addr show and ensure that a new device, ppp0, is available.

To connect to your VPN normally, simply execute:

# pon <TUNNEL>

Where <TUNNEL> is the name of the tunnel you established earlier. Note that this command should be run as root.

Routing

Once you have connected to your VPN, you should be able to interact with anything available on the VPN server. To access anything on the remote network, you need to add a new route to your routing table.

Note: Depending on your configuration, you may need to re-add the routing information every time you connect to your VPN.

For more information on how to add routes, you can read this article which has many more examples: PPTP Routing Howto

Split Tunneling

Packets with a destination of your VPN's network should be routed through the VPN interface (usually ppp0). To do this, you create the route:

# ip route add 192.168.10.0/24 dev ppp0

This will route all the traffic with a destination of 192.168.10.* through your VPN's interface, (ppp0).

Route All Traffic

It may be desirable to route all traffic through your VPN connection. You can do this by running:

# ip route add default dev ppp0

Note: Routing all traffic through the VPN may result in slower over all connection speed because your traffic will be routed through the remote VPN before being routed normally.

Route All Traffic by /etc/ppp/ip-up.d

Note: All scripts in /etc/ppp/ip-up.d/ will called when the VPN connection is established.

/etc/ppp/ip-up.d/01-routes.sh

#!/bin/bash

# This script is called with the following arguments:
# Arg Name
# $1 Interface name
# $2 The tty
# $3 The link speed
# $4 Local IP number
# $5 Peer IP number
# $6 Optional ``ipparam'' value foo

ip route add default via $4

Make sure the script is executable.

Split Tunneling based on port by /etc/ppp/ip-up.d

Note: All scripts in /etc/ppp/ip-up.d/ will called when the VPN connection is established.

/etc/ppp/ip-up.d/01-routebyport.sh

#!/bin/bash

# This script is called with the following arguments:
# Arg Name
# $1 Interface name
# $2 The tty
# $3 The link speed
# $4 Local IP number
# $5 Peer IP number
# $6 Optional ``ipparam'' value foo

echo 0 > /proc/sys/net/ipv4/conf/$1/rp_filter
echo 1 > /proc/sys/net/ipv4/ip_forward
echo 1 > /proc/sys/net/ipv4/ip_dynaddr

ip route flush table vpn
ip route add default via $5 dev $1 table vpn

# forward only IRC ports over VPN
iptables -t mangle -A OUTPUT -p tcp -m multiport --dports 6667,6697 -j MARK --set-mark 0x1
iptables -t nat    -A POSTROUTING -o $1 -j MASQUERADE

ip rule  add fwmark 0x1 pri 100 lookup vpn
ip rule  add from $4 pri 200 table vpn
ip route flush cache

Make sure the script is executable and that the vpn table is added to /etc/iproute2/rt_tables

201 vpn

Disconnect

Execute the following to disconnect from a VPN:

# poff <TUNNEL>

<TUNNEL> is the name of your tunnel.

Making A VPN Daemon and Connecting On Boot

You can create a simple daemon for your VPN connection by creating an appropriate /etc/rc.d/* script:

Note: As always, <TUNNEL> is the name of your tunnel. <ROUTING COMMAND> is the command you use to add the appropriate route to the routing table.

Note: The stop functionality of this script will not work if the updetach and persist arguments are passed to /usr/bin/pon when pon is started. The reason for this is that the /usr/bin/poff script contains a bug when determining the PID of the specified pppd process if arguments were passed to pon.

To resolve this issue, you can patch your /usr/bin/poff file by making the following changes on line 93:

-PID=`ps axw | grep "[ /]pppd call $1 *\$" | awk '{print $1}'`
+PID=`ps axw | grep "[ /]pppd call $1" | awk '{print $1}'`

/etc/rc.d/name-of-your-vpn

#!/bin/bash

. /etc/rc.conf
. /etc/rc.d/functions

DAEMON=<TUNNEL>-vpn
ARGS=

[ -r /etc/conf.d/$DAEMON ] && . /etc/conf.d/$DAEMON

case "$1" in
 start)
   stat_busy "Starting $DAEMON"
   pon <TUNNEL> updetach persist &>/dev/null && <ROUTING COMMAND> &>/dev/null
   if [ $? = 0 ]; then
     add_daemon $DAEMON
     stat_done
   else
     stat_fail
     exit 1
   fi
   ;;
 stop)
   stat_busy "Stopping $DAEMON"
   poff <TUNNEL> &>/dev/null
   if [ $? = 0 ]; then
     rm_daemon $DAEMON
     stat_done
   else
     stat_fail
     exit 1
   fi
   ;;
 restart)
   $0 stop
   sleep 1
   $0 start
   ;;
 *)
   echo "usage: $0 {start|stop|restart}"  
esac

Note: We call pon in the script with two additional arguments: updetach and persist. The argument updetach makes pon block until the connection has been established. The other argument, persist, makes the network automatically reconnect in the event of a failure. To connect at boot add @<TUNNEL>-vpn to the end of your DAEMONS array in /etc/rc.conf.

Troubleshooting

If client connections keep timing out with "LCP: timeout sending Config-Requests", make sure that GRE is allowed through the client firewall. For iptables, the necessary command is:

iptables -A INPUT -p 47 -j ACCEPT

Alternatively, if you only want to allow PPTP traffic that corresponds to a connection request coming from your local machine, you can use the conntrack PPTP helper:

iptables -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT 
iptables -t raw -A OUTPUT -p tcp --dport 1723 -j CT --helper pptp

The second line should autoload the nf_conntrack_pptp and nf_conntrack_proto_gre kernel modules, which are needed for this.

If you get “EAP: unknown authentication type 26; Naking”, open /etc/ppp/options.pptp and commented out the lines refuse-chap and refuse-mschap and add the options file entry to the tunnel file like this:

/etc/ppp/peers/<tunel>

# written by pptpsetup
pty "pptp vpn.foo.com --nolaunchpppd"
lock
noauth
nobsdcomp
nodeflate
name USERNAME
remotename vpn
file /etc/ppp/options.pptp
ipparam vpn
require-mppe-128

Remarks

You can find more information about configuring pptpclient at their website: pptpclient website. The contents of this article were adapted from their Ubuntu How-To which also provides some hints on how to do things such as connecting on boot. These examples should be easy to adapt into daemons or other scripts to help automate your configuration.