Configure a VPN tunnel between Linux and Windows XP

In this post I would be showin you the steps needed to create a tunnel between Linux and Windows XP for safe data transmission with proper data encapsulation. We will be using Openswan on the Linux server and IPsec on the Windows XP to do so.

Linux side configuration

Make sure you have openswan package installed on your machine. I will be using Redhat 6.2 so the commands I am using might vary as per other distros.

Install the required package using yum

# yum -y install openswan

# vi /etc/ipsec.conf

version 2.0 # conforms to second version of ipsec.conf specification

# basic configuration
config setup
# Debug-logging controls: "none" for (almost) none, "all" for lots.
# klipsdebug=none
# plutodebug="control parsing"
# For Red Hat Enterprise Linux and Fedora, leave protostack=netkey
protostack=netkey
nat_traversal=yes
virtual_private=
oe=off
# Enable this if you see "failed to find any available worker"
# nhelpers=0
interfaces=%defaultroute

klipsdebug=none
plutodebug=none
overridemtu=1410

conn %default
keyingtries=1

conn sample
right=%any
left=%defaultroute
authby=secret
auto=add
keylife=24h
rekey=no
keyingtries=0
pfs=no

conn packetdefault
auto=ignore

conn private-or-clear
auto=ignore
Now you need to define the preshared key which will be used for authentication

# vi /etc/ipsec.secrets
: PSK "secretkey"
# service ipsec start

Windows XP side configuration

Open the "run" prompt and launch "mmc console"

Now go to File and click on "Add/Remove Snap-in"

Now add "IP Security Policies on Local Computer"

Create a new IP security policy

Mention the preshared key as provided in ip.secrets on the linux server

Then you can click on Next and Finish the wizard.

Now edit the properties of this policy. Click on "Filter Action" on the tab menu and add a new custom action

Then you can finish the wizard and select this filter action for the IPsec policy.

Now edit the Filter properties. (Here 192.168.0.138 is my Linux server IP)

Similarly create another IP Filter rule with the name "Linux to WinXP" and add the custom Filter action to this filter rule. The only thing you need to change is the filter properties.