This article describes a basic installation and configuration of OpenVPN, suitable for private and small business use. For more detailed information, please see the OpenVPN 2.3 man page and the OpenVPN documentation. OpenVPN is a robust and highly flexible VPN daemon. It supports SSL/TLS security, Ethernet bridging, TCP or UDP tunnel transport through proxies or NAT. Additionally it has support for dynamic IP addresses and DHCP, scalability to hundreds or thousands of users, and portability to most major OS platforms.
OpenVPN is tightly bound to the OpenSSL library, and derives much of its crypto capabilities from it. It supports conventional encryption using a pre-shared secret key (Static Key mode) or public key security (SSL/TLS mode) using client & server certificates. Additionally it supports unencrypted TCP/UDP tunnels.
OpenVPN is designed to work with the TUN/TAP virtual networking interface that exists on most platforms. Overall, it aims to offer many of the key features of IPSec but with a relatively lightweight footprint. OpenVPN was written by James Yonan and is published under the GNU General Public License (GPL).
- 1 Install OpenVPN
- 2 Kernel configuration
- 3 Connect to a VPN provided by a third party
- 4 Create a Public Key Infrastructure (PKI) from scratch
- 5 A basic L3 IP routing configuration
- 6 Starting OpenVPN
- 7 Routing all client traffic through the server
- 8 L3 IPv4 routing
- 9 DNS
- 10 L2 Ethernet bridging
- 11 Troubleshooting
- 12 See Also
Install the package.
OpenVPN requires TUN/TAP support, which is already configured in the default kernel. If you build your own kernel, make sure to enable the
tun module as below:
Kernel config file
Device Drivers --> Network device support [M] Universal TUN/TAP device driver support
Read Kernel modules for more information.
Connect to a VPN provided by a third party
To connect to a VPN service provided by a third party, most of the following can most likely be ignored, especially regarding server setup. Most likely you will want to begin with #The client configuration file and skip ahead to #Starting OpenVPN after that. Use the certificates and instructions given by your provider, for instance see: Airvpn.
Create a Public Key Infrastructure (PKI) from scratch
If you are setting up OpenVPN from scratch, you will need to create a Public Key Infrastructure (PKI).
Create the needed certificates and keys using the easy-rsa scripts.
The final step of the key creation process is to copy the files needed to the correct machines through a secure channel.
The public ca.crt certificate is needed on all servers and clients. The private ca.key key is secret and only needed on the key generating machine.
A server needs server.crt, dh2048.pem (public), server.key, and ta.key (private).
A client needs client.crt (public), client.key, and ta.key (private).
A basic L3 IP routing configuration
OpenVPN is an extremely versatile piece of software and many configurations are possible, in fact machines can be both "servers" and "clients", blurring the distinction between server and client.
What really distinguishes a server from a client (apart from the type of certificate used) is the configuration file itself. The OpenVPN daemon start-up script reads all the .conf configuration files it finds in
/etc/openvpn on start-up and acts accordingly. If it finds more than one configuration file, it will start one OpenVPN process per configuration file.
This article explains how to set up a server named elmer and a client that connects to it named bugs. More servers and clients can easily be added by creating more key/certificate pairs and adding more server and client configuration files.
The OpenVPN package comes with a collection of example configuration files for different purposes. The sample server and client configuration files make an ideal starting point for a basic OpenVPN setup with the following features:
- Uses Public Key Infrastructure (PKI) for authentication.
- Creates a VPN using a virtual TUN network interface (OSI L3 IP routing).
- Listens for client connections on UDP port 1194 (OpenVPN's official IANA port number).
- Distributes virtual addresses to connecting clients from the 10.8.0.0/24 subnet.
The server configuration file
Copy the example server configuration file to
# cp /usr/share/openvpn/examples/server.conf /etc/openvpn/server.conf
Edit the following:
dhparameters to reflect the path and names of the keys and certificates. Specifying the paths will allow you to run the OpenVPN executable from any directory for testing purposes.
- Enable the SSL/TLS HMAC handshake protection. Note the use of the parameter 0 for a server.
- It is recommended to run OpenVPN with reduced privileges once it has initialized. Do this by uncommenting the
ca /etc/openvpn/ca.crt cert /etc/openvpn/elmer.crt key /etc/openvpn/elmer.key dh /etc/openvpn/dh2048.pem . . tls-auth /etc/openvpn/ta.key 0 . . user nobody group nobody
The client configuration file
Copy the example client configuration file to
# cp /usr/share/openvpn/examples/client.conf /etc/openvpn/client.conf
Edit the following:
remotedirective to reflect either the server's Fully Qualified Domain Name, hostname (as known to the client), or its IP address.
- Uncomment the
groupdirectives to drop privileges.
keyparameters to reflect the path and names of the keys and certificates.
- Enable the SSL/TLS HMAC handshake protection. Note the use of the parameter 1 for a client.
remote elmer.acmecorp.org 1194 . . user nobody group nobody ca /etc/openvpn/ca.crt cert /etc/openvpn/bugs.crt key /etc/openvpn/bugs.key . . tls-auth /etc/openvpn/ta.key 1
Drop root privileges after connecting
Using the options
user nobody and
group nobody in the configuration file makes openvpn drop its privileges after establishing the connection. The downside is that upon VPN disconnect the daemon is unable to delete its set network routes again. If one wants to limit transmitting traffic without the VPN connection, this may be advantageous. However, it requires manual action to delete the routes and will, hence, often be undesired. For this case the OpenVPN howto explains how to create an unprivileged user mode and wrapper script to have the routes restored automatically.
Further, it is possible to let OpenVPN start as a non-privileged user in the first place, without ever running as root, see this OpenVPN wiki page.
Testing the OpenVPN configuration
# openvpn /etc/openvpn/server.conf on the server, and
# openvpn /etc/openvpn/client.conf on the client. You should see something similar to this:
# openvpn /etc/openvpn/server.conf
Wed Dec 28 14:41:26 2011 OpenVPN 2.2.1 x86_64-unknown-linux-gnu [SSL] [LZO2] [EPOLL] [eurephia] built on Aug 13 2011 Wed Dec 28 14:41:26 2011 NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables Wed Dec 28 14:41:26 2011 Diffie-Hellman initialized with 2048 bit key . . Wed Dec 28 14:41:54 2011 bugs/18.104.22.168:48904 MULTI: primary virtual IP for bugs/22.214.171.124:48904: 10.8.0.6 Wed Dec 28 14:41:57 2011 bugs/126.96.36.199:48904 PUSH: Received control message: 'PUSH_REQUEST' Wed Dec 28 14:41:57 2011 bugs/188.8.131.52:48904 SENT CONTROL [bugs]: 'PUSH_REPLY,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.6 10.8.0.5' (status=1)
# openvpn /etc/openvpn/client.conf
Wed Dec 28 14:41:50 2011 OpenVPN 2.2.1 i686-pc-linux-gnu [SSL] [LZO2] [EPOLL] [eurephia] built on Aug 13 2011 Wed Dec 28 14:41:50 2011 NOTE: OpenVPN 2.1 requires '--script-security 2' or higher to call user-defined scripts or executables Wed Dec 28 14:41:50 2011 LZO compression initialized . . Wed Dec 28 14:41:57 2011 GID set to nobody Wed Dec 28 14:41:57 2011 UID set to nobody Wed Dec 28 14:41:57 2011 Initialization Sequence Completed
On the server, find the IP address assigned to the tunX device:
# ip addr show
. . 40: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100 link/none inet 10.8.0.1 peer 10.8.0.2/32 scope global tun0
Here we see that the server end of the tunnel has been given the IP address 10.8.0.1.
Do the same on the client:
# ip addr show
. . 37: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100 link/none inet 10.8.0.6 peer 10.8.0.5/32 scope global tun0
And the client side has been given the IP address 10.8.0.6.
Now try pinging the interfaces.
On the server:
# ping -c3 10.8.0.6
PING 10.8.0.6 (10.8.0.6) 56(84) bytes of data. 64 bytes from 10.8.0.6: icmp_req=1 ttl=64 time=238 ms 64 bytes from 10.8.0.6: icmp_req=2 ttl=64 time=237 ms 64 bytes from 10.8.0.6: icmp_req=3 ttl=64 time=205 ms --- 10.8.0.6 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2002ms rtt min/avg/max/mdev = 205.862/227.266/238.788/15.160 ms
On the client:
# ping -c3 10.8.0.1
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data. 64 bytes from 10.8.0.1: icmp_req=1 ttl=64 time=158 ms 64 bytes from 10.8.0.1: icmp_req=2 ttl=64 time=158 ms 64 bytes from 10.8.0.1: icmp_req=3 ttl=64 time=157 ms --- 10.8.0.1 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 157.426/158.278/158.940/0.711 ms
You now have a working OpenVPN installation, and your client (bugs) will be able to use services on the server (elmer), and vice versa.
Configure the MTU with Fragment and MSS
Now it is time to configure the maximum segment size (MSS). In order to do this we need to discover what is the smallest MTU along the path between the client and server. In order to do this you can ping the server and disable fragmentation. Then specify the max packet size.
# ping -c5 -M do -s 1500 elmer.acmecorp.org
PING elmer.acmecorp.org (184.108.40.206) 1500(1528) bytes of data. From 220.127.116.11 (18.104.22.168) icmp_seq=1 Frag needed and DF set (mtu = 576) From 22.214.171.124 (126.96.36.199) icmp_seq=1 Frag needed and DF set (mtu = 576) From 188.8.131.52 (184.108.40.206) icmp_seq=1 Frag needed and DF set (mtu = 576) From 220.127.116.11 (18.104.22.168) icmp_seq=1 Frag needed and DF set (mtu = 576) From 22.214.171.124 (126.96.36.199) icmp_seq=1 Frag needed and DF set (mtu = 576) --- core.myrelay.net ping statistics --- 0 packets transmitted, 0 received, +5 errors
We received an ICMP message telling us the MTU is 576 bytes. The means we need to fragment the UDP packets smaller then 576 bytes to allow for some UDP overhead.
# ping -c5 -M do -s 548 elmer.acmecorp.org
PING elmer.acmecorp.org (188.8.131.52) 548(576) bytes of data. 556 bytes from 184.108.40.206: icmp_seq=1 ttl=48 time=206 ms 556 bytes from 220.127.116.11: icmp_seq=2 ttl=48 time=224 ms 556 bytes from 18.104.22.168: icmp_seq=3 ttl=48 time=206 ms 556 bytes from 22.214.171.124: icmp_seq=4 ttl=48 time=207 ms 556 bytes from 126.96.36.199: icmp_seq=5 ttl=48 time=208 ms --- myrelay.net ping statistics --- 5 packets transmitted, 5 received, 0% packet loss, time 4001ms rtt min/avg/max/mdev = 206.027/210.603/224.158/6.832 ms
After some trial and error..., we discover that we need to fragment packets on 548 bytes. In order to do this we specify this fragment size in the configuration and instruct OpenVPN to fix the Maximum Segment Size (MSS).
remote elmer.acmecorp.org 1194 . . fragment 548 mssfix 548 . . user nobody group nobody . . ca /etc/openvpn/ca.crt cert /etc/openvpn/bugs.crt key /etc/openvpn/bugs.key . . tls-auth /etc/openvpn/ta.key 1
We also need to tell the server about the fragmentation. Note that "mssfix" is NOT needed in the server configuration.
ca /etc/openvpn/ca.crt cert /etc/openvpn/elmer.crt key /etc/openvpn/elmer.key dh /etc/openvpn/dh2048.pem . . tls-auth /etc/openvpn/ta.key 0 . . user nobody group nobody . . fragment 548
You can also allow OpenVPN to do this for you by having OpenVPN do the ping testing every time the client connects to the VPN. Be patient, since your client may not inform you about the test being run and the connection may appear as nonfunctional until finished.
remote elmer.acmecorp.org 1194 . . mtu-test . . user nobody group nobody . . ca /etc/openvpn/ca.crt cert /etc/openvpn/bugs.crt key /etc/openvpn/bugs.key . . tls-auth /etc/openvpn/ta.key 1
Connect to the server via IPv6
In order to enable Dual Stack for OpenVPN, you have to change
proto udp to
proto udp6 in both server.conf and client.conf. Afterwards both IPv4 and IPv6 are enabled.
Provide IPv6 inside the tunnel
In order to provide IPv6 inside the tunnel, you need to have a IPv6 prefix routed to your OpenVPN server. Either set up a static route on your gateway (if you have a static block assigned), or use a DHCPv6 client to get a prefix with DHCPv6 Prefix delegation (see IPv6 Prefix delegation for details). You can also use a unique local address from the address block fc00::/7. Both methods have advantages and disadvantages:
- Many ISPs only provide dynamically changing IPv6 prefixes. OpenVPN does not support prefix changes, so you need to change your server.conf every time the prefix is changed (Maybe can be automated with a script).
- ULA addresses are not routed to the Internet, and setting up NAT is not as straightforward as with IPv4. So you cannot route the entire traffic over the tunnel. If you only want to connect two sites via IPv6, without the need to connect to the Internet over the tunnel, the ULA addresses may be easier to use.
After you have received a prefix (a /64 is recommended), append the following to the server.conf:
This is the IPv6 equivalent to the default 10.8.0.0/24 network of OpenVPN and needs to be taken from the DHCPv6 client. Or use for example fd00:1234::/64.
If you want to push a route to your home network (192.168.1.0/24 equivalent), also append:
push "route-ipv6 2001:db8:0:abc::/64"
OpenVPN does not yet include DHCPv6, so there is no method to e.g. push DNS server over IPv6. This needs to be done with IPv4. The OpenVPN Wiki provides some other configuration options.
To troubleshoot a VPN connection, start the client's daemon manually with
openvpn /etc/openvpn/client.conf as root. The server can be started the same way using its own configuration file (e.g.,
systemd service configuration
To start OpenVPN automatically at system boot, either for a client or for a server, enable
openvpn@<configuration>.service on the applicable machine.
For example, if the client configuration file is
/etc/openvpn/client.conf, the service name is
firstname.lastname@example.org. Or, if the server configuration file is
/etc/openvpn/server.conf, the service name is
Letting NetworkManager start a connection
On a client you might not always need to run a VPN tunnel and/or only want to establish it for a specific NetworkManager connection. This can be done by adding a script to
/etc/NetworkManager/dispatcher.d/. In the following example "Provider" is the name of the NetworkManager connection:
#!/bin/bash case "$2" in up) if [ "$CONNECTION_ID" == "Provider" ]; then systemctl start openvpn@client fi ;; down) systemctl stop openvpn@client ;; esac
See NetworkManager#Network services with NetworkManager dispatcher for more details.
If you would like to connect a client to an OpenVPN server through Gnome's built-in network configuration do the following. First, install
networkmanager-openvpn. Then go to the Settings menu and choose Network. Click the plus sign to add a new connection and choose VPN. From there you can choose OpenVPN and manually enter the settings. You can also choose to import #The client configuration file, if you have already created one. Yet, be aware NetworkManager does not show error messages for options it does not import. To connect to the VPN simply turn the connection on and check the options are applied as you configured (e.g. via
journalctl -b --u NetworkManager).
Routing all client traffic through the server
By default only traffic directly to and from an OpenVPN server passes through the VPN. To have all traffic, including web traffic, pass through the VPN do the following. First add the following to your server's configuration file (i.e.,
push "redirect-gateway def1 bypass-dhcp" push "dhcp-option DNS 10.8.0.1"
10.8.0.1 to your preferred DNS IP address.
If you have problems with non responsive DNS after connecting to server, install BIND as simple DNS forwarder and push the IP address of the OpenVPN server as DNS to clients.
Additionally, if you want to allow clients to be able to reach other (private) subnets behind the server, you may want to use the
push "route <address pool> <subnet>" option:
push "route 188.8.131.52 255.255.255.0" push "route 172.20.142.0 255.255.255.0"
After setting up your configuration file, you need to enable packet forwarding on the server. Additionally, your server's firewall will need to be set up to allow VPN traffic through it, which is described below for both ufw and iptables.
In order to configure your ufw settings for VPN traffic first add the following to
/etc/ufw/before.rules, and add the following code after the header and before the "*filter" line. Do not forget to change the IP/subnet mask to match the one in
/etc/openvpn/server.conf. The adapter ID in the example is generically called
eth0 so edit it for your system accordingly.
# NAT (Network Address Translation) table rules *nat :POSTROUTING ACCEPT [0:0] # Allow traffic from clients to eth0 -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE # do not delete the "COMMIT" line or the NAT table rules above will not be processed COMMIT
Open OpenVPN port 1194:
# ufw allow 1194
Lastly, reload UFW:
# ufw reload
In order to allow VPN traffic through your iptables firewall of your server, first create an iptables rule for NAT forwarding  on the server, assuming the interface you want to forward to is named
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
If you have difficulty pinging the server through the VPN, you may need to add explicit rules to open up TUN/TAP interfaces to all traffic. If that is the case, do the following :
iptables -A INPUT -i tun+ -j ACCEPT iptables -A FORWARD -i tun+ -j ACCEPT iptables -A INPUT -i tap+ -j ACCEPT iptables -A FORWARD -i tap+ -j ACCEPT
Additionally be sure to accept connections from the OpenVPN port (default 1194) and through the physical interface.
When you are satisfied make the changes permanent as shown in iptables#Configuration and usage.
Prevent leaks if vpn goes down
The idea is simple: prevent all traffic through our default interface (enp3s0 for example) and only allow tun0. If the openvpn connection drops, your computer will lose its internet access and therefore, avoid your programs to continue connecting through an insecure network adapter.
Be sure to set up a script to restart openvpn if it goes down if you do not want to manually restart it.
# Default policies ufw default deny incoming ufw default deny outgoing # Openvpn interface (adjust interface accordingly to your configuration) ufw allow in on tun0 ufw allow out on tun0 # Local Network (adjust ip accordingly to your configuration) ufw allow in on enp3s0 from 192.168.1.0/24 ufw allow out on enp3s0 to 192.168.1.0/24 # Openvpn (adjust port accordingly to your configuration) ufw allow out on enp3s0 to any port 1194 ufw allow in on enp3s0 from any port 1194
L3 IPv4 routing
This section describes how to connect client/server LANs to each other using L3 IPv4 routing.
Prerequisites for routing a LAN
For a host to be able to forward IPv4 packets between the LAN and VPN, it must be able to forward the packets between its NIC and its tun/tap device. See Internet sharing#Enable packet forwarding for configuration details.
By default, all IP packets on a LAN addressed to a different subnet get sent to the default gateway. If the LAN/VPN gateway is also the default gateway, there is no problem and the packets get properly forwarded. If not, the gateway has no way of knowing where to send the packets. There are a couple of solutions to this problem.
- Add a static route to the default gateway routing the VPN subnet to the LAN/VPN gateway's IP address.
- Add a static route on each host on the LAN that needs to send IP packets back to the VPN.
- Use iptables' NAT feature on the LAN/VPN gateway to masquerade the incoming VPN IP packets.
Connect the server LAN to a clientThe server is on a LAN using the 10.66.0.0/24 subnet. To inform the client about the available subnet, add a push directive to the server configuration file:
push "route 10.66.0.0 255.255.255.0"
Connect the client LAN to a server
- Any subnets used on the client side, must be unique and not in use on the server or by any other client. In this example we will use 192.168.4.0/24 for the clients LAN.
- Each client's certificate has a unique Common Name, in this case bugs.
- The server may not use the duplicate-cn directive in its config file.
Create a client configuration directory on the server. It will be searched for a file named the same as the client's common name, and the directives will be applied to the client when it connects.
# mkdir -p /etc/openvpn/ccd
Create a file in the client configuration directory called bugs, containing the
iroute 192.168.4.0 255.255.255.0 directive. It tells the server what subnet should be routed to the client:
iroute 192.168.4.0 255.255.255.0
Add the client-config-dir and the
route 192.168.4.0 255.255.255.0 directive to the server configuration file. It tells the server what subnet should be routed from the tun device to the server LAN:
client-config-dir ccd route 192.168.4.0 255.255.255.0
Connect both the client and server LANs
Combine the two previous sections:
push "route 10.66.0.0 255.255.255.0" . . client-config-dir ccd route 192.168.4.0 255.255.255.0
iroute 192.168.4.0 255.255.255.0
Connect clients and client LANsBy default clients will not see each other. To allow IP packets to flow between clients and/or client LANs, add a client-to-client directive to the server configuration file:
In order for another client or client LAN to see a specific client LAN, you will need to add a push directive for each client subnet to the server configuration file (this will make the server announce the available subnet(s) to other clients):
client-to-client push "route 192.168.4.0 255.255.255.0" push "route 192.168.5.0 255.255.255.0" . .
The DNS servers used by the system are defined in
/etc/resolv.conf. Traditionally, this file is the responsibility of whichever program deals with connecting the system to the network (e.g. Wicd, NetworkManager, etc...) However, OpenVPN will need to modify this file if you want to be able to resolve names on the remote side. To achieve this in a sensible way, install , which makes it possible for more than one program to modify
resolv.conf without stepping on each-other's toes.
Before continuing, test openresolv by restarting your network connection and ensuring that
resolv.conf states that it was generated by resolvconf, and that your DNS resolution still works as before. You should not need to configure openresolv; it should be automatically detected and used by your network system.
For Linux, OpenVPN can send DNS host information, but expects an external process to act on it. This can be done with a openvpn-update-resolv-conf script, which can be saved for example at
/etc/openvpn/update-resolv-conf and make it executable with chmod. There is also an AUR package: AUR which will take care of the script installation for you.
Once the script is installed add lines like the following into your OpenVPN client configuration file:
script-security 2 up /etc/openvpn/update-resolv-conf down /etc/openvpn/update-resolv-conf
Now, when your launch your OpenVPN connection, you should find that your resolv.conf file is updated accordingly, and also returns to normal when your close the connection.
L2 Ethernet bridging
For now see: OpenVPN Bridge
If you are having resolve issues when starting your profile:
# journalctl _SYSTEMD_UNITemail@example.com
RESOLVE: Cannot resolve host address: example.com: Name or service not known
Then, only if your network setup can be started before OpenVPN, you should force OpenVPN to wait for the network by adding
After=network.target to the OpenVPN systemd service file:
[Unit] Description=OpenVPN connection to %i Requires=network.target After=network.target ...
Do not forget to run
systemctl daemon-reload and restart
Client daemon not restarting after suspend
If you put your client system to sleep, and on resume openvpn does not restart, resulting in broken connectivity, create the following file:
#!/bin/sh if [ "$1" == "pre" ] then killall openvpn fi
Make it executable
chmod a+x /usr/lib/systemd/system-sleep/vpn.sh
Connection drops out after some time of inactivity
If the VPN-Connection drops some seconds after it stopped transmitting data and, even though it states it is connected, no data can be transmitted through the tunnel, try adding a
keepalivedirective to the server's configuration:
. . keepalive 10 120 . .
In this case the server will send ping-like messages to all of its clients every
10 seconds, thus keeping the tunnel up.
If the server does not receive a response within
120 seconds from a specific client, it will assume this client is down.
A small ping-interval can increase the stability of the tunnel, but will also cause slightly higher traffic. Depending on your connection, also try lower intervals than 10 seconds.