How to use the command 'openvpn' (with examples)
OpenVPN is an open-source virtual private network (VPN) solution that allows users to securely connect to remote networks over the internet. It provides encryption and authentication to ensure the confidentiality and integrity of data transmitted between the client and server. In this article, we will explore several use cases of the ‘openvpn’ command with examples.
Use case 1: Connect to server using a config file
Code:
sudo openvpn path/to/client.conf
Motivation: Connecting to a server using a config file is a convenient way to establish a VPN connection without manually configuring the connection settings. It eliminates the need to remember and enter all the necessary parameters every time you want to connect.
Explanation: The ‘sudo openvpn’ command is used to start the OpenVPN client. The ‘path/to/client.conf’ argument specifies the path to the client configuration file, which contains the required connection settings.
Example output:
Wed Sep 15 14:30:42 2021 OpenVPN 2.5.3 x86_64-apple-darwin [SSL (OpenSSL)] [LZO] [LZ4] [Pthread] [AEAD] built on Jun 28 2021
...
Wed Sep 15 14:30:45 2021 Initialization Sequence Completed
Use case 2: Try to set up an insecure peer-to-peer tunnel
Code:
sudo openvpn --remote alice.example.com --dev tun1 --ifconfig 10.4.0.1 10.4.0.2
Motivation: Setting up an insecure peer-to-peer tunnel can be useful for testing or debugging purposes. It allows direct communication between two hosts without encryption, which may be necessary in certain scenarios.
Explanation: The ‘sudo openvpn’ command is used to start the OpenVPN client. The ‘–remote’ option specifies the remote host to connect to. The ‘–dev’ option specifies the virtual tunnel device name. The ‘–ifconfig’ option sets the IP addresses for the tunnel endpoints.
Example output:
Wed Sep 15 14:35:14 2021 OpenVPN 2.5.3 x86_64-apple-darwin [SSL (OpenSSL)] [LZO] [LZ4] [Pthread] [AEAD] built on Jun 28 2021
...
Wed Sep 15 14:35:16 2021 Initialization Sequence Completed
Use case 3: Connect to a host without encryption
Code:
sudo openvpn --remote bob.example.com --dev tun1 --ifconfig 10.4.0.2 10.4.0.1
Motivation: Connecting to a host without encryption can be useful in certain cases where encryption is not necessary or desired. For example, when establishing a local network between trusted devices.
Explanation: The ‘sudo openvpn’ command is used to start the OpenVPN client. The ‘–remote’ option specifies the remote host to connect to. The ‘–dev’ option specifies the virtual tunnel device name. The ‘–ifconfig’ option sets the IP addresses for the tunnel endpoints.
Example output:
Wed Sep 15 14:39:58 2021 OpenVPN 2.5.3 x86_64-apple-darwin [SSL (OpenSSL)] [LZO] [LZ4] [Pthread] [AEAD] built on Jun 28 2021
...
Wed Sep 15 14:40:00 2021 Initialization Sequence Completed
Use case 4: Create a cryptographic key and save it to file
Code:
openvpn --genkey secret path/to/key
Motivation: Creating a cryptographic key is essential for establishing a secure VPN connection. The generated key can be used for encryption and decryption of data transmitted between the client and server.
Explanation: The ‘openvpn’ command with the ‘–genkey secret’ option is used to generate a cryptographic key. The ‘path/to/key’ argument specifies the file path to save the generated key.
Example output:
Secret key generated at path/to/key
Use case 5: Set up a peer-to-peer tunnel with a static key
Code:
sudo openvpn --remote alice.example.com --dev tun1 --ifconfig 10.4.0.1 10.4.0.2 --secret path/to/key
Motivation: Setting up a peer-to-peer tunnel with a static key can provide a higher level of security compared to an insecure tunnel. The static key ensures that only parties possessing the key can establish a connection.
Explanation: The ‘sudo openvpn’ command is used to start the OpenVPN client. The ‘–remote’ option specifies the remote host to connect to. The ‘–dev’ option specifies the virtual tunnel device name. The ‘–ifconfig’ option sets the IP addresses for the tunnel endpoints. The ‘–secret’ option specifies the path to the static key file.
Example output:
Wed Sep 15 14:46:32 2021 OpenVPN 2.5.3 x86_64-apple-darwin [SSL (OpenSSL)] [LZO] [LZ4] [Pthread] [AEAD] built on Jun 28 2021
...
Wed Sep 15 14:46:33 2021 Initialization Sequence Completed
Use case 6: Connect to a host with the same static key
Code:
sudo openvpn --remote bob.example.com --dev tun1 --ifconfig 10.4.0.2 10.4.0.1 --secret path/to/key
Motivation: Connecting to a host with the same static key allows establishing a secure and authenticated VPN connection. It ensures that both parties possess the same key and can securely communicate with each other.
Explanation: The ‘sudo openvpn’ command is used to start the OpenVPN client. The ‘–remote’ option specifies the remote host to connect to. The ‘–dev’ option specifies the virtual tunnel device name. The ‘–ifconfig’ option sets the IP addresses for the tunnel endpoints. The ‘–secret’ option specifies the path to the static key file.
Example output:
Wed Sep 15 14:51:26 2021 OpenVPN 2.5.3 x86_64-apple-darwin [SSL (OpenSSL)] [LZO] [LZ4] [Pthread] [AEAD] built on Jun 28 2021
...
Wed Sep 15 14:51:28 2021 Initialization Sequence Completed
Conclusion:
The ‘openvpn’ command provides a versatile way to establish VPN connections with different configuration options. Whether you need to connect using a config file, set up a secure tunnel, or create cryptographic keys, OpenVPN offers flexibility and security. By understanding the various use cases and examples covered in this article, you can leverage the power of OpenVPN for your networking needs.
