Openvpn

Introduction

OpenVPN is an open source Virtual Private Network (VPN), which allows one to establish a tunnel for any IP subnetwork or virtual ethernet adapter e.i. TUN/TAP kernel device over any UDP/TCP port. At freegeek, we have one between our wireless and wired networks.

Installation

• on debian

apt-get install openvpn openssl resolvconf

• gentoo

echo "ssl examples" >> /etc/portage/package.use
emerge -av openvpn resolvconf-gentoo

• Other

can be found here: http://openvpn.net/install.html

Setup

Once installed you will need to set some things up.

Here is a sample config (though you will need to edit a few lines). Copy and save this as /etc/openvpn/client.conf .

# both '#' and ';' act as comments
client
dev tun
proto udp
# change this to your server's address
remote ASK_A_SYSADMIN 1194
resolv-retry infinite
nobind
persist-key
persist-tun
tls-client
ca /etc/openvpn/keys/ca.crt
cert /etc/openvpn/keys/my.crt
key /etc/openvpn/keys/my.key
ns-cert-type server
tls-auth /etc/openvpn/keys/ta.key 1
cipher BF-CBC
comp-lzo
up /etc/openvpn/freegeek-up.sh

That last line refers to a script, which you should copy from here:

#!/bin/bash
TEMPFILE=`mktemp /tmp/resolv.conf.XXXXXX`
echo search fglan >> $TEMPFILE
for DHCPOPTVAR in ${!foreign_option*} ; do
    DHCPOPT="${!DHCPOPTVAR}"
    if echo $DHCPOPT | grep -qe '^dhcp-option.DNS' ; then
        echo $DHCPOPT | sed -re 's/dhcp-option.DNS.([0-9.]+)$/nameserver \1/' >> $TEMPFILE
    fi
done
cat $TEMPFILE | resolvconf -a $dev
rm $TEMPFILE

So, now the keys

if you read that configuration file, you would have seen ca.crt, foo.crt, and foo.key, and later on ta.key. you can't connect to the vpn without those files!

so ask a sysadmin to run the following commands on our vpn server:

cd /etc/openvpn/easy-rsa
. ./vars
./build-key clientname

and then securely copy over those, plus ca.crt and ta.key, to your computer and put them in an unreadable directory, /etc/openvpn/keys/ . don't leave any spare copies of those files lying around!

TODO

• teach the computers to run the following automatically on connecting to freegeek's wireless:

openvpn --config /etc/openvpn/client.conf