Routing Traffic With OpenVPN

Don’t you love messages like “This video is not available in your country”. That generally means it is not available outside the USA (unless you are in Germany in which case it means it is available anywhere but your country). They have finally annoyed me enough to do something about it and my web server is based in the USA so it should be easy… Right?

It turns out that while it should be easy, it took me far longer than expected, mainly because I found most tutorials assume you know things. Also, I found the Arch wiki not to be great in this area (and as you may notice below, I am not the person to fix it). So here is yet another “guide” on how to set up OpenVPN on your server and getting both Linux and Windows clients to access it (mainly posted as notes in case I need to set this up again in the future).

Step #1: OpenVPN

The first thing that needs done is the creation of a personal Certificate Authority and generating the needed keys for your server. Fortunately, OpenVPN comes with a set of scripts called easy-rsa. I am not going to cover this as these scripts are well documented and do all the work for you.

I am also not going into all the configuration of OpenVPN. But here is an /etc/openvpn/server.conf file I found to work:

dev tun
proto udp
port 1194
ca ca.crt
cert server.crt
key server.key
dh dh1024.pem
user nobody
group nobody
push "redirect-gateway def1"
push "dhcp-option DNS"
log-append /var/log/openvpn

Not that the configuration file can be called anything you want. OpenVPN is launched using “systemctl start openvpn@server.service“, where “server” in this case is because my configuration file is “server.conf“.

The only bit of configuration I will directly mention is setting up users to be able to access the VPN using a username/password approach rather than generating individual keys for each client. This is purely because I am a lazy admin and everyone I want to use my VPN has an SFTP shell on my server already. Just add this to your server configuration file:

plugin /usr/lib/openvpn/plugins/ login

OpenVPN does give warnings about this configuration, so consider the security implications if you use it.

Step #2: Enable forwarding
By default, packet forwarding is disabled. You can see this by running:

$ cat /proc/sys/net/ipv4/ip_forward

We can enable this by adding these lines to /etc/sysctl.conf:

# Packet forwarding
net.ipv4.ip_forward = 1
net.inet.ip.fastforwarding = 1

Note that the file /etc/sysctl.conf is not going to be used from systemd-207 onwards, so this will need to be move the appropriate place. Also, the “fastforwarding” line is purely based on anecdotes I found on the internet, and may not do anything at all! In fact, I think it is a BSD thing, so I have no idea why I am mentioning it. Moving on…

Step #3: iptables

If you have iptables running, you will need to open up access to the VPN. You also have to forward the VPN client traffic through to the internet. This is the bit I found least documented anywhere. Also, I am not an iptables expert, so while this works, it might not be the best approach:

# OpenVPN
iptables -A INPUT -i eth0 -m state --state NEW -p udp --dport 1194 -j ACCEPT
# Allow TUN interface connections to OpenVPN server
iptables -A INPUT -i tun+ -j ACCEPT
# Allow TUN interface connections to be forwarded through other interfaces
iptables -A FORWARD -i tun+ -j ACCEPT
iptables -A FORWARD -i tun+ -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o tun+ -m state --state RELATED,ESTABLISHED -j ACCEPT
# NAT the VPN client traffic to the internet
iptables -t nat -A POSTROUTING -s -o eth0 -j MASQUERADE

If your default iptables OUTPUT value is not ACCEPT, you will also need a line like:

iptables -A OUTPUT -o tun+ -j ACCEPT

I have not tested that set-up, so you may need more.

Step 4: Clients
I went with using NetworkManager on Linux and the OpenVPN client on Windows. Note the two different Windows clients on that site are exactly the same, so there is no need to figure out the difference.

The Windows client requires a “.ovpn configuration file. Here is an example:

dev tun
proto udp
remote 1194
resolv-retry infinite
ca foobar.crt
verb 3

The only thing to note here is the “ca” line is the public certificate you generated in Step #1. Even with password authentication, you still need to provide that certificate. Also, it is important to have the compression setting being the same in both the server and client configuration. Given I mostly want to use the VPN for video, I have not enabled compression.

And there you have it. Configuring that took me much too much time, but now I can pretend to be in the USA and watch all the content that is geolocked to there that I want. Which as it turns out, is not often. I have only watched one video in the month since I set this up. Good use of my time…

5 thoughts on “Routing Traffic With OpenVPN

  1. I’ve set up a similar OpenVPN configuration, but with selective routes. I looked up some Services IP ranges, like Netflix, Youtube, Hulu or Grooveshark. Most of them are not availabe in Germany. I published that configuration on my github profile. I am certain it can refine your setup too, because most of your traffic goes through your original connection and only the video/audio traffic is routed through the slower VPN tunnel.

    You can review the configs here:

  2. Just use SSH’s support for SOCKS5 proxy. I use it all the time with my VPS, it’s reliable, easy to setup and works for any service I tried so far.