I recently had a need to install a VPN service in a OpenVZ container. Since I normally only use Hardware emulating VM’s I ran into quite a few issues in terms of low-level networking support on this Container Virtualisation System. Turns out that you are stuck with a TUN/TAP solution as most services won’t enable PPP services on their infrastructure. Also Ethernet bridging is not available (at least on the service I used) so you’re stuck with NAT IP masquerading. Considering the options I thought best served with using OpenVPN server.
yum --enablerepo=epel -y install openvpn
cp /usr/share/doc/openvpn-*/sample-config-files/server.conf /etc/openvpn/
These are the contents of /etc/openvpn/server.conf
local XXX.XXX.XXX.XXX #Server External IP
key SERVER.key #keep file secret
server 10.8.0.0 255.255.255.0
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 184.108.40.206" #using Google Public DNS
push "dhcp-option DNS 220.127.116.11" #using Google Public DNS
keepalive 10 120
mkdir -p /etc/openvpn/easy-rsa/keys
cp -rf /usr/share/openvpn/easy-rsa/2.0/* .
#Set the country (KEY_COUNTRY)
#organisation name (KEY_ORG)
#support email (KEY_EMAIL)
Create certificate authority
The CA key and certificate should not be in the keys directory inside the easy-rsa directory.
Create certificate for the server
Answer the questions and commit the certificate into the database
Create the Diffie Hellman files
These files are used for the actual key exchange to ensure the confidentiality over an insecure channel, aka the Internet. Based on the length of the key used (KEY_SIZE) it may take a while.
Copy crypto files
cp ca.crt SERVER.crt SERVER.key dh1024.pem /etc/openvpn/
Create the certificate for each client
Enable IP Forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward
NAT Masquerading Setup
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o venet0 -j MASQUERADE
chkconfig openvpn on
apt-get install network-manager-openvpn
- Ensure that the client settings reflect EXACTLY the server setting (I learned the hard way wasting a lot of time on troubleshooting the fact that routing would not work – turned out to be a client setting ‘comp-lzo’ !)
- Ensure TUN/TAP services are enabled for your OpenVZ container (http://wiki.openvz.org/VPN_via_the_TUN/TAP_device)
ERROR: Linux ip link set failed: external program exited with error status: 255