If you want more than just pre-shared keys OpenVPN makes it easy to setup and use a Public Key Infrastructure (PKI) to use SSL/TLS certificates for authentication and key exchange between the VPN server and clients. OpenVPN can be used in a routed or bridged VPN mode and can be configured to use either UDP or TCP. The port number can be configured as well, but port 1194 is the official one. And it is only using that single port for all communication. VPN client implementations are available for almost anything including all Linux distributions, OS X, Windows and OpenWRT based WLAN routers.

To install openvpn in a terminal enter:

1. Install OVPN's easy client on Mac OS X. OVPNs client is the easiest, and securest way to protect your OS X computer.
2. Download Viscosity (Mac OS 10.7 or later is required). Viscosity is an OpenVPN client with intuitive interface offering complete configuration of OpenVPN connections on Mac OS. Viscosity is an OpenVPN client with intuitive interface offering complete configuration of OpenVPN connections on Mac OS.

The first step in building an OpenVPN configuration is to establish a PKI (public key infrastructure). The PKI consists of:

Unlike other similar providers, OVPN does offer compatible clients for Windows and Mac OS X. We downloaded the Windows client and installed it to see how well it worked and we were highly impressed with clean, streamline the structure of the client.

• a separate certificate (also known as a public key) and private key for the server and each client, and

• a master Certificate Authority (CA) certificate and key which is used to sign each of the server and client certificates.

OpenVPN supports bidirectional authentication based on certificates, meaning that the client must authenticate the server certificate and the server must authenticate the client certificate before mutual trust is established.

Both server and client will authenticate the other by first verifying that the presented certificate was signed by the master certificate authority (CA), and then by testing information in the now-authenticated certificate header, such as the certificate common name or certificate type (client or server).

To setup your own Certificate Authority (CA) and generating certificates and keys for an OpenVPN server and multiple clients first copy the easy-rsa directory to /etc/openvpn. This will ensure that any changes to the scripts will not be lost when the package is updated. From a terminal change to user root and:

Next, edit /etc/openvpn/easy-rsa/vars adjusting the following to your environment:

Enter the following to generate the master Certificate Authority (CA) certificate and key:

Next, we will generate a certificate and private key for the server:

As in the previous step, most parameters can be defaulted. Two other queries require positive responses, 'Sign the certificate? [y/n]' and '1 out of 1 certificate requests certified, commit? [y/n]'.

Diffie Hellman parameters must be generated for the OpenVPN server:

All certificates and keys have been generated in the subdirectory keys/. Common practice is to copy them to /etc/openvpn/:

The VPN client will also need a certificate to authenticate itself to the server. Usually you create a different certificate for each client. To create the certificate, enter the following in a terminal while being user root:

Copy the following files to the client using a secure method:

• /etc/openvpn/ca.crt

• /etc/openvpn/easy-rsa/keys/client1.crt

• /etc/openvpn/easy-rsa/keys/client1.key

As the client certificates and keys are only required on the client machine, you should remove them from the server.

Along with your OpenVPN installationyou got these sample config files (and many more if if you check):

Start with copying and unpacking server.conf.gz to /etc/openvpn/server.conf.

Edit /etc/openvpn/server.conf to make sure the following lines are pointing to the certificates and keys you created in the section above.

Edit /etc/sysctl.conf and uncomment the following line to enable IP forwarding.

Then reload sysctl.

That is the minimum you have to configure to get a working OpenVPN server. You can use all the default settings in the sample server.conf file. Now start the server. You will find logging and error messages in your via journal. Dependin on what you look for:

If you started a templatized service openvpn@server you can filter for this particular message source with:

Be aware that the 'systemctl start openvpn' is not starting your openvpn you just defined.Openvpn uses templatized systemd jobs, openvpn@CONFIGFILENAME.So if for example your configuration file is 'server.conf' your service is called openvpn@server.You can run all kind of service and systemctl commands like start/stop/enable/disable/preset against a templatized service like openvpn@server.

You can enable/disable various openvpn services on one system, but you could also let Ubuntu do the heavy lifting.There is config for AUTOSTART in /etc/default/openvpn.Allowed values are 'all', 'none' or space separated list ofnames of the VPNs. If empty, 'all' is assumed.The VPN name refers to the VPN configutation file name.i.e. 'home' would be /etc/openvpn/home.confIf you're running systemd, changing this variable willrequire running 'systemctl daemon-reload' followed bya restart of the openvpn service (if you removed entriesyou may have to stop those manually)After 'systemctl daemon-reload' a restart of the 'generic' openvon will restart all dependentservices that the generator in /lib/systemd/system-generators/openvpn-generator created foryour conf files when you called daemon-reload.

That is the minimum you have to configure to get a working OpenVPN server.You can use all the default settings in the sample server.conf file. Now start the server. You will find logging and error messages in your journal.

Now check if OpenVPN created a tun0 interface:

There are various different OpenVPN client implementationswith and without GUIs. You can read more about clients in a later section.For now we use the OpenVPN client for Ubuntu which is the same executable as the server. So you have to install the openvpn package again on the client machine:

This time copy the client.conf sample config file to /etc/openvpn/.

Copy the client keys and the certificate of the CA you created in the section above to e.g. /etc/openvpn/ and edit /etc/openvpn/client.conf to make sure the following lines are pointing to those files. If you have the files in /etc/openvpn/ you can omit the path.

And you have to at least specify the OpenVPN server name or address.Make sure the keyword client is in the config. That's what enablesclient mode.

Also, make sure you specify the keyfile names you copied from the server

Now start the OpenVPN client:

Check if it created a tun0 interface:

Check if you can ping the OpenVPN server:

The OpenVPN server always uses the first usable IP address in the client network and only that IP is pingable. E.g. if you configured a /24 for the client network mask, the .1 address will be used. The P-t-P address you see in the ifconfig output above is usually not answering ping requests.

Check out your routes:

If the above didn't work for you, check this:

• Check your journal, e.g. journalctl --identifier ovpn-server (for server.conf)

• Check that you have specified the keyfile names correctly in client.conf and server.conf.

• Can the client connect to the server machine? Maybe a firewall is blocking access? Check journal on server.

• Client and server must use same protocol and port, e.g. UDP port 1194, see port and proto config option

• Client and server must use same config regarding compression, see comp-lzo config option

• Client and server must use same config regarding bridged vs routed mode, see server vs server-bridge config option

The above is a very simple working VPN. The client can access services on the VPN server machine through an encrypted tunnel. If you want to reach more servers or anything in other networks, push some routes to the clients. E.g. if your company's network can be summarized to the network 192.168.0.0/16, you could push this route to the clients. But you will also have to change the routing for the way back - your servers need to know a route to the VPN client-network.

Or you might push a default gateway to all the clients to send all their internet traffic to the VPN gateway first and from there via the company firewall into the internet. This section shows you some possible options.

Push routes to the client to allow itto reach other private subnets behindthe server. Remember that theseprivate subnets will also needto know to route the OpenVPN clientaddress pool (10.8.0.0/24)back to the OpenVPN server.

If enabled, this directive will configureall clients to redirect their defaultnetwork gateway through the VPN, causingall IP traffic such as web browsing andDNS lookups to go through the VPN(the OpenVPN server machine or your central firewall may need to NATthe TUN/TAP interface to the internet in order for this to work properly).

Configure server mode and supply a VPN subnetfor OpenVPN to draw client addresses from.The server will take 10.8.0.1 for itself,the rest will be made available to clients.Each client will be able to reach the serveron 10.8.0.1. Comment this line out if you areethernet bridging.

Maintain a record of client to virtual IP addressassociations in this file. If OpenVPN goes down oris restarted, reconnecting clients can be assignedthe same virtual IP address from the pool that waspreviously assigned.

Push DNS servers to the client.

Allow client to client communication.

Enable compression on the VPN link.

The keepalive directive causes ping-likemessages to be sent back and forth overthe link so that each side knows whenthe other side has gone down.Ping every 1 second, assume that remotepeer is down if no ping received duringa 3 second time period.

It's a good idea to reduce the OpenVPN daemon's privileges after initialization.

OpenVPN 2.0 includes a feature that allows the OpenVPN server to securely obtain a username and password from a connecting client, and to use that information as a basis for authenticating the client.To use this authentication method, first add the auth-user-pass directive to the client configuration. It will direct the OpenVPN client to query the user for a username/password, passing it on to the server over the secure TLS channel.

This will tell the OpenVPN server to validate theusername/password entered by clients using the login PAM module.Useful if you have centralized authentication with e.g. Kerberos.

Please read the OpenVPN hardening security guide for further security advice.

OpenVPN can be setup for either a routed or a bridged VPN mode. Sometimes this is also referred to as OSI layer-2 versus layer-3 VPN. In a bridged VPN all layer-2 frames - e.g. all ethernet frames - are sent to the VPN partners and in a routed VPN only layer-3 packets are sent to VPN partners.In bridged mode all traffic including traffic which was traditionally LAN-local like local network broadcasts, DHCP requests, ARP requests etc. are sent to VPN partners whereas in routed mode this would be filtered.

First, use netplan to configure a bridge device using the desired ethernetdevice.

Static IP addressing is highly suggested. DHCP addressing can also work,but you will still have to encode a static address in the OpenVPN configuration file.

The next step on the server is to configure the ethernet device forpromiscuous mode on boot. To do this, ensure thenetworkd-dispatcher package is installed and createthe following configuration script.

Then add the following contents.

Edit /etc/openvpn/server.conf to use tap rather than tun and set the server to use the server-bridge directive:

After configuring the server, restart openvpn by entering:

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First, install openvpn on the client:

Then with the server configured and the client certificates copied to the /etc/openvpn/ directory, create a client configuration file by copying the example. In a terminal on the client machine enter:

Now edit /etc/openvpn/client.conf changing the following options:

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Finally, restart openvpn:

You should now be able to connect to the remote LAN through the VPN.

Many Linux distributions including Ubuntu desktop variants come with Network Manager,a nice GUI to configure your network settings. It also can manage your VPN connections. Make sure you have package network-manager-openvpn installed. Here you see that the installation installs all other required packages as well:

To inform network-manager about the new installed packages you will have to restart it:

Open the Network Manager GUI, select the VPN tab and then the 'Add' button. Select OpenVPNas the VPN type in the opening requester and press 'Create'. In the next windowadd the OpenVPN's servername as the 'Gateway', set 'Type' to 'Certificates (TLS)', point 'User Certificate'to your user certificate, 'CA Certificate' to your CA certificate and 'Private Key'to your private key file. Use the advanced button to enable compression (e.g. comp-lzo), dev tap, or otherspecial settings you set on the server. Now try to establish your VPN.

Tunnelblick is an excellent free, open source implementation of a GUI for OpenVPN for OS X.The project's homepage is at http://code.google.com/p/tunnelblick/. Download the latest OS X installer from there and install it. Then put your client.ovpn config file together with the certificates and keys in/Users/username/Library/Application Support/Tunnelblick/Configurations/ and lauch Tunnelblick from your Application folder.

First download and install the latest OpenVPN Windows Installer. OpenVPN 2.3.2 was the latest when this was written.As of this writing, the management GUI is included with the Windows binary installer.

You need to start the OpenVPN service. Goto Start > Computer > Manage > Services and Applications > Services. Find the OpenVPN service and start it. Set it's startup type to automatic. When you start the OpenVPN MI GUI the first time you need to run it as an administrator. You have to right click on it and you will see that option.

You will have to write your OpenVPN config in a textfile and place it in C:Program FilesOpenVPNconfigclient.ovpn along with the CA certificate. You could put the user certificate in the user's home directory like in the follwing example.

Note: If you are not using user authentication and/or you want to run the service without user interaction, comment out the following options:

You may want to set the Windows service to 'automatic'.

OpenWRT is described as a Linux distribution for embedded devices like WLAN router.There are certain types of WLAN routers who can be flashed to run OpenWRT.Depending on the available memory on your OpenWRT router you can run software likeOpenVPN and you could for example build a small inexpensive branch office router with VPN connectivityto the central office.More info on OpenVPN on OpenWRT is here. And here is the OpenWRT project's homepage: http://openwrt.org

Log into your OpenWRT router and install OpenVPN:

Check out /etc/config/openvpn and put your client config in there. Copy certificates and keys to /etc/openvpn/

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Restart OpenVPN on OpenWRT router to pick up the config

You will have to see if you need to adjust your router's routing and firewall rules.

• See the OpenVPN website for additional information.

• Also, Pakt's OpenVPN: Building and Integrating Virtual Private Networks is a good resource.

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