How to install and use OpenVPN¶
OpenVPN is a flexible, reliable and secure Virtual Private Networking (VPN) solution. It belongs to the family of SSL/TLS VPN stacks (different from IPsec VPNs). This chapter will show how to install and configure OpenVPN to create a VPN.
Install the server¶
To install OpenVPN, run the following command in your terminal:
sudo apt install openvpn easy-rsa
Set up the Public Key Infrastructure (PKI)¶
If you want more than just pre-shared keys, OpenVPN makes it easy to set up 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; this single port is used for all communication. VPN client implementations are available for almost anything including all Linux distributions, macOS, Windows and OpenWRT-based WLAN routers.
The first step in building an OpenVPN configuration is to establish a PKI, which consists of:
A separate certificate (also known as a public key) and private key for the server and each client
A primary Certificate Authority (CA) certificate and key, used to sign the server and client certificates
OpenVPN supports bi-directional 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 the server and the client will authenticate each other by first verifying that the presented certificate was signed by the primary 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).
Create server keys and certificates¶
Next, we will generate a key pair for the server:
./easyrsa gen-req myservername nopass
pki/dh.pem:
./easyrsa gen-dh
And finally, create a certificate for the server:
./easyrsa sign-req server myservername
All certificates and keys have been generated in subdirectories. Common practice is to copy them to /etc/openvpn/:
cp pki/dh.pem pki/ca.crt pki/issued/myservername.crt pki/private/myservername.key /etc/openvpn/
Simple server configuration¶
Included with your OpenVPN installation are these (and many more) sample configuration files:
/usr/share/doc/openvpn/examples/sample-config-files/client.conf
/usr/share/doc/openvpn/examples/sample-config-files/server.conf
If these files under /usr/share/doc/* are not available (for example, the system was provisioned as a minimal install), you can fetch them directly from the Ubuntu package repositories:
Start by copying the example server configuration to /etc/openvpn/myserver.conf:
sudo cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf /etc/openvpn/myserver.conf
In Ubuntu 20.04 or older, the file is compressed, so do this instead:
sudo cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz /etc/openvpn/myserver.conf.gz
sudo gzip -d /etc/openvpn/myserver.conf.gz
Edit /etc/openvpn/myserver.conf to make sure the following lines are pointing to the certificates and keys you created in the section above.
ca ca.crt
cert myservername.crt
key myservername.key
dh dh.pem
tls-auth ta.key 0
Complete this set with a TLS Authentication (TA) key in /etc/openvpn for tls-auth like this:
sudo openvpn --genkey secret ta.key
Add a config file to /etc/sysctl.conf.d to enable IP forwarding:
echo "net.ipv4.ip_forward = 1" | sudo tee /etc/sysctl.d/50-enable-ipv4-forwarding.conf
Then apply this file through sysctl:
sudo sysctl -p /etc/sysctl.d/50-enable-ipv4-forwarding.conf
This is the minimum you need to configure to get a working OpenVPN server.
You can consider studying and tweaking all the default settings we got from the sample server.conf file.
Now you can start the server.
sudo systemctl start openvpn@myserver
Note
Be aware that the systemctl start openvpn is not starting the openvpn you just defined.
OpenVPN uses templated systemd jobs, openvpn@CONFIGFILENAME. So if, for example, your configuration file is myserver.conf your service is called openvpn@myserver. You can run all kinds of service and systemctl commands like start/stop/enable/disable/preset against a templated service like openvpn@server.
You will find logging and error messages in the journal. For example, if you started a templated service openvpn@server you can filter for this particular message source with:
sudo journalctl -u openvpn@myserver -xe
The same templated approach works for all of systemctl:
sudo systemctl status openvpn@myserver
Which shows the current server status:
Loaded: loaded (/usr/lib/systemd/system/openvpn@.service; disabled; preset: enabled)
Active: active (running) since Wed 2026-01-21 10:38:01 UTC; 37s ago
Invocation: b2a3d68935e7423e8f822bc0c88db764
Docs: man:openvpn(8)
https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage
https://community.openvpn.net/openvpn/wiki/HOWTO
Main PID: 10556 (openvpn)
Status: "Initialization Sequence Completed"
Tasks: 1 (limit: 10)
Memory: 1.7M (peak: 1.9M)
CPU: 17ms
CGroup: /system.slice/system-openvpn.slice/openvpn@myserver.service
└─10556 /usr/sbin/openvpn --daemon ovpn-myserver --status /run/openvpn/myserver.status 10 --cd /etc/openvpn --script-security 2 --config /etc/openvpn/myserver.conf --writepid /r>
Jan 21 10:38:01 server ovpn-myserver[10556]: net_iface_up: set tun0 up
Jan 21 10:38:01 server ovpn-myserver[10556]: net_addr_v4_add: 10.8.0.1/24 dev tun0
Jan 21 10:38:01 server ovpn-myserver[10556]: Could not determine IPv4/IPv6 protocol. Using AF_INET
Jan 21 10:38:01 server ovpn-myserver[10556]: Socket Buffers: R=[212992->212992] S=[212992->212992]
Jan 21 10:38:01 server ovpn-myserver[10556]: UDPv4 link local (bound): [AF_INET][undef]:1194
Jan 21 10:38:01 server ovpn-myserver[10556]: UDPv4 link remote: [AF_UNSPEC]
Jan 21 10:38:01 server ovpn-myserver[10556]: MULTI: multi_init called, r=256 v=256
Jan 21 10:38:01 server ovpn-myserver[10556]: IFCONFIG POOL IPv4: base=10.8.0.2 size=253
Jan 21 10:38:01 server ovpn-myserver[10556]: IFCONFIG POOL LIST
Jan 21 10:38:01 server ovpn-myserver[10556]: Initialization Sequence Completed
You can enable/disable various OpenVPN services on one system, but you could also let Ubuntu do it for you. There is a config for AUTOSTART in /etc/default/openvpn. Allowed values are “all”, “none” or a space-separated list of names of the VPNs. If empty, “all” is assumed. The VPN name refers to the VPN configuration file name, i.e., home would be /etc/openvpn/home.conf.
If you’re running systemd, changing this variable requires running systemctl daemon-reload followed by a restart of the openvpn service (if you removed entries you may have to stop those manually).
After systemctl daemon-reload, a restart of the “generic” OpenVPN will restart all dependent services that the generator in /lib/systemd/system-generators/openvpn-generator created for your conf files when you called daemon-reload.
Now, check if OpenVPN created a tun0 interface:
ip addr show dev tun0
Due to restricting it to dev tun0 this will report just that:
5: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 100
link/none
inet 10.8.0.1 peer 10.8.0.2/32 scope global tun0
valid_lft forever preferred_lft forever
inet6 fe80::b5ac:7829:f31e:32c5/64 scope link stable-privacy
valid_lft forever preferred_lft forever
Create client certificates¶
The VPN client will also need a certificate to authenticate itself to the server. Usually you create a different certificate for each client.
This can be done either on the server (as with the keys and certificates above) and then securely distributed to the client, or the client can generate and submit a request that is sent and signed by the server.
To create the certificate, enter the following in a terminal as a root user:
./easyrsa gen-req myclient1 nopass && ./easyrsa sign-req client myclient1
If the first command above was done on a remote system, then copy the .req file to the CA server. From there, you can import it via easyrsa import-req /incoming/myclient1.req myclient1. Then you can go on with the second sign-req command.
After this is done, in both cases you will need to copy the following files to the client using a secure method:
pki/ca.crtpki/issued/myclient1.crtpki/private/myclient1.keyta.key
Since the client certificates and keys are only required on the client machine, you can remove them from the server.
Simple client configuration¶
There are various different OpenVPN client implementations – both with and without GUIs. You can read more about clients in our page on OpenVPN Clients. For now, we use the command-line/service-based OpenVPN client for Ubuntu, which is part of the same package as the server. So you must install the openvpn package again on the client machine:
sudo apt install openvpn
This time, copy the client.conf sample config file to /etc/openvpn/:
sudo cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf /etc/openvpn/
Copy the following client keys and certificate files 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:
ca ca.crt
cert myclient1.crt
key myclient1.key
tls-auth ta.key 1
And you have to specify the OpenVPN server name or address. Make sure the keyword client is in the config file, since that’s what enables client mode.
client
remote vpnserver.example.com 1194
Now start the OpenVPN client with the same templated mechanism:
sudo systemctl start openvpn@client
You can check the status as you did on the server:
sudo systemctl status openvpn@client
Which shows the current client status:
● openvpn@client.service - OpenVPN connection to client
Loaded: loaded (/usr/lib/systemd/system/openvpn@.service; disabled; preset: enabled)
Active: active (running) since Wed 2026-01-21 10:54:27 UTC; 55s ago
Invocation: f65eae29fc8e4403bd06236309a1db2c
Docs: man:openvpn(8)
https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage
https://community.openvpn.net/openvpn/wiki/HOWTO
Main PID: 11361 (openvpn)
Status: "Initialization Sequence Completed"
Tasks: 1 (limit: 10)
Memory: 1.9M (peak: 2.1M)
CPU: 22ms
CGroup: /system.slice/system-openvpn.slice/openvpn@client.service
└─11361 /usr/sbin/openvpn --daemon ovpn-client --status /run/openvpn/client.status 10 --cd /etc/openvpn --script-security 2 --config /etc/openvpn/client.conf --writepid /run/openvpn/client.pid
Jan 21 10:54:27 client systemd[1]: Starting openvpn@client.service - OpenVPN connection to client...
Jan 21 10:54:27 client ovpn-client[11361]: Note: --cipher is not set. OpenVPN versions before 2.5 defaulted to BF-CBC as fallback when cipher negotiation failed in this case. If you need this fallback please add '--data-ciphers-fallback BF-CBC' to your configuration and/or add BF-CBC to --data-ciphers.
Jan 21 10:54:27 client ovpn-client[11361]: Note: Kernel support for ovpn-dco missing, disabling data channel offload.
Jan 21 10:54:27 client ovpn-client[11361]: OpenVPN 2.6.15 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] [DCO]
Jan 21 10:54:27 client ovpn-client[11361]: library versions: OpenSSL 3.5.3 16 Sep 2025, LZO 2.10
Jan 21 10:54:27 client systemd[1]: Started openvpn@client.service - OpenVPN connection to client.
Jan 21 10:54:27 client ovpn-client[11361]: DCO version: N/A
Jan 21 10:54:27 client ovpn-client[11361]: TCP/UDP: Preserving recently used remote address: [AF_INET]10.185.198.84:1194
Jan 21 10:54:27 client ovpn-client[11361]: Socket Buffers: R=[212992->212992] S=[212992->212992]
Jan 21 10:54:27 client ovpn-client[11361]: UDPv4 link local: (not bound)
Jan 21 10:54:27 client ovpn-client[11361]: UDPv4 link remote: [AF_INET]10.185.198.84:1194
Jan 21 10:54:27 client ovpn-client[11361]: TLS: Initial packet from [AF_INET]10.185.198.84:1194, sid=46d7b1e7 da534d2d
Jan 21 10:54:27 client ovpn-client[11361]: VERIFY OK: depth=1, CN=server
Jan 21 10:54:27 client ovpn-client[11361]: VERIFY KU OK
Jan 21 10:54:27 client ovpn-client[11361]: Validating certificate extended key usage
Jan 21 10:54:27 client ovpn-client[11361]: ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
Jan 21 10:54:27 client ovpn-client[11361]: VERIFY EKU OK
Jan 21 10:54:27 client ovpn-client[11361]: VERIFY OK: depth=0, CN=server
Jan 21 10:54:27 client ovpn-client[11361]: Control Channel: TLSv1.3, cipher TLSv1.3 TLS_AES_256_GCM_SHA384, peer certificate: 2048 bits RSA, signature: RSA-SHA256
Jan 21 10:54:27 client ovpn-client[11361]: [server] Peer Connection Initiated with [AF_INET]10.185.198.84:1194
Jan 21 10:54:27 client ovpn-client[11361]: TLS: move_session: dest=TM_ACTIVE src=TM_INITIAL reinit_src=1
Jan 21 10:54:27 client ovpn-client[11361]: TLS: tls_multi_process: initial untrusted session promoted to trusted
Jan 21 10:54:27 client ovpn-client[11361]: PUSH: Received control message: 'PUSH_REPLY,route-gateway 10.8.0.1,topology subnet,ping 10,ping-restart 120,ifconfig 10.8.0.2 255.255.255.0,peer-id 1,cipher AES-256-GCM,protocol-flags cc-exit tls-ekm dyn-tls-crypt,tun-mtu 1500'
Jan 21 10:54:27 client ovpn-client[11361]: OPTIONS IMPORT: --ifconfig/up options modified
Jan 21 10:54:27 client ovpn-client[11361]: OPTIONS IMPORT: route-related options modified
Jan 21 10:54:27 client ovpn-client[11361]: OPTIONS IMPORT: tun-mtu set to 1500
Jan 21 10:54:27 client ovpn-client[11361]: TUN/TAP device tun0 opened
Jan 21 10:54:27 client ovpn-client[11361]: net_iface_mtu_set: mtu 1500 for tun0
Jan 21 10:54:27 client ovpn-client[11361]: net_iface_up: set tun0 up
Jan 21 10:54:27 client ovpn-client[11361]: net_addr_v4_add: 10.8.0.2/24 dev tun0
Jan 21 10:54:27 client ovpn-client[11361]: Initialization Sequence Completed
On the server log, an incoming connection looks like the following (you can see client name and source address as well as success/failure messages):
ovpn-myserver[10556]: read UDPv4 [ECONNREFUSED]: Connection refused (fd=7,code=111)
ovpn-myserver[10556]: 10.185.198.41:40732 VERIFY OK: depth=1, CN=server
ovpn-myserver[10556]: 10.185.198.41:40732 VERIFY OK: depth=0, CN=client
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_VER=2.6.15
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_PLAT=linux
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_TCPNL=1
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_MTU=1600
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_NCP=2
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_CIPHERS=AES-256-GCM:AES-128-GCM:CHACHA20-POLY1305
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_PROTO=990
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_LZO_STUB=1
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_COMP_STUB=1
ovpn-myserver[10556]: 10.185.198.41:40732 peer info: IV_COMP_STUBv2=1
ovpn-myserver[10556]: 10.185.198.41:40732 TLS: move_session: dest=TM_ACTIVE src=TM_INITIAL reinit_src=1
ovpn-myserver[10556]: 10.185.198.41:40732 TLS: tls_multi_process: initial untrusted session promoted to trusted
ovpn-myserver[10556]: 10.185.198.41:40732 Control Channel: TLSv1.3, cipher TLSv1.3 TLS_AES_256_GCM_SHA384, peer certificate: 2048 bits RSA, signature: RSA-SHA256, peer temporary key: 768 bits X25519MLKEM768
ovpn-myserver[10556]: 10.185.198.41:40732 [client] Peer Connection Initiated with [AF_INET]10.185.198.41:40732
ovpn-myserver[10556]: MULTI: new connection by client 'client' will cause previous active sessions by this client to be dropped. Remember to use the --duplicate-cn option if you want multiple clients using the same certificate or username to concurrently connect.
ovpn-myserver[10556]: MULTI_sva: pool returned IPv4=10.8.0.2, IPv6=(Not enabled)
ovpn-myserver[10556]: MULTI: Learn: 10.8.0.2 -> client/10.185.198.41:40732
ovpn-myserver[10556]: MULTI: primary virtual IP for client/10.185.198.41:40732: 10.8.0.2
ovpn-myserver[10556]: SENT CONTROL [client]: 'PUSH_REPLY,route-gateway 10.8.0.1,topology subnet,ping 10,ping-restart 120,ifconfig 10.8.0.2 255.255.255.0,peer-id 0,cipher AES-256-GCM,protocol-flags cc-exit tls-ekm dyn-tls-crypt,tun-mtu 1500' (status=1)
ovpn-myserver[10556]: client/10.185.198.41:40732 Data Channel: cipher 'AES-256-GCM', peer-id: 0
ovpn-myserver[10556]: client/10.185.198.41:40732 Timers: ping 10, ping-restart 240
ovpn-myserver[10556]: client/10.185.198.41:40732 Protocol options: explicit-exit-notify 1, protocol-flags cc-exit tls-ekm dyn-tls-crypt
And you can check on the client if it created a tun0 interface:
ip addr show dev tun0
Showing the tun0 device on the client:
6: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 500
link/none
inet 10.8.0.2/24 brd 10.8.0.255 scope global tun0
valid_lft forever preferred_lft forever
inet6 fe80::3c08:9432:f898:d1c0/64 scope link stable-privacy proto kernel_ll
valid_lft forever preferred_lft forever
Check if you can ping the OpenVPN server:
ping 10.8.0.1 -c 1
Which should show a working ping with an answer:
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data.
64 bytes from 10.8.0.1: icmp_seq=1 ttl=64 time=0.335 ms
Note
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 ip addr output above does not usually answer ping requests.
Check out your routes:
ip route show dev tun0
A system might have many many routes, but this call restricts to those on tun0:
10.8.0.0/24 proto kernel scope link src 10.8.0.2
First troubleshooting¶
If the above didn’t work for you, check the following:
Check your
journal -xe, also consider limiting it to the unit with-uas done in the examples shown above.Check that you have specified the key filenames correctly in the client and server
conffiles.Can the client connect to the server machine? Maybe a firewall is blocking access? Check the journal on the server.
Client and server must use same protocol and port, e.g. UDP port 1194, see
portandprotoconfig options.Client and server must use the same compression configuration, see
comp-lzoconfig option.Client and server must use same config regarding bridged vs. routed mode, see
server vs server-bridgeconfig optionClient must use the config
tls-authwith index1(example client config:tls-auth ta.key 1), but server must usetls-authwith index0(example server config:tls-auth ta.key 0).
Advanced configuration¶
Advanced routed VPN configuration on server¶
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 summarised 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.
The example config files that we have been using in this guide are full of these advanced options in the form of a comment and a disabled configuration line as an example.
Note
Read the OpenVPN hardening security guide for further security advice.
Advanced bridged VPN configuration on server¶
OpenVPN can be set up 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.
Prepare interface config for bridging on server¶
First, use Netplan to configure a bridge device using the desired Ethernet device like /etc/netplan/01-netcfg.yaml to contain:
network:
version: 2
renderer: networkd
ethernets:
enp0s31f6:
dhcp4: no
bridges:
br0:
interfaces: [enp0s31f6]
dhcp4: no
addresses: [10.0.1.100/24]
routes:
- to: default
via: 10.0.1.1
nameservers:
addresses: [10.0.1.1]
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 for promiscuous mode on boot. To do this, ensure the networkd-dispatcher package is installed and create the following configuration script:
sudo apt update && sudo apt install networkd-dispatcher
Then add the following contents to a file like /etc/networkd-dispatcher/dormant.d/promisc_bridge:
#!/bin/sh
set -e
if [ "$IFACE" = br0 ]; then
# no networkd-dispatcher event for 'carrier' on the physical interface
ip link set enp0s31f6 up promisc on
fi
And ensure it has the permission to be executed:
sudo chmod +x /etc/networkd-dispatcher/dormant.d/promisc_bridge
Prepare server config for bridging¶
Edit /etc/openvpn/server.conf to use tap rather than tun and set the server to use the server-bridge directive:
;dev tun
dev tap
;server 10.8.0.0 255.255.255.0
server-bridge 10.0.0.4 255.255.255.0 10.0.0.128 10.0.0.254
After configuring the server, restart OpenVPN by entering:
sudo systemctl restart openvpn@myserver
Prepare client config for bridging¶
The only difference on the client side for bridged mode to what was outlined above is that you need to edit /etc/openvpn/client.conf and set tap mode:
dev tap
;dev tun
Finally, restart OpenVPN:
sudo systemctl restart openvpn@client
You should now be able to connect to the fully remote LAN through the VPN.
Using OpenSSL providers¶
OpenVPN uses the OpenSSL 3 Default Provider on Ubuntu. However, you can include additional providers dynamically depending on your use case.
Legacy provider¶
You can still use legacy algorithms in Ubuntu, this is not recommended but might
be required to support older clients not yet compatible with the more secure new algorithms.
Enabling those is done by explicitly adding them through the legacy provider alongside default.
To do this, add the following line to your OpenVPN configuration.
providers legacy default
You can also run openvpn with the --providers argument.
openvpn --providers legacy default ...
Note
On Ubuntu 22.04 LTS and earlier, legacy algorithms are included in OpenVPN by default.
TPM 2.0¶
OpenVPN also works with Trusted Platform Module (TPM) 2.0 encryption using the tpm2 provider. Set it up by installing the tpm2-openssl package and including both legacy and tpm2 in your provider configuration.
providers legacy default tpm2
Alternatively, run with:
openvpn --providers legacy default tpm2 ...
Note
The provider order matters here as tpm2 currently requires the legacy provider to load first.
Further reading¶
OpenVPN as a snap easy-openvpn
Debian’s OpenVPN Guide