How to use the command 'openconnect' (with examples)

OpenConnect is a versatile VPN client primarily used for connecting to Cisco AnyConnect VPNs but also compatible with other types of VPN protocols. This tool is essential for establishing secure connections to remote networks, essential for maintaining privacy and security when accessing sensitive information over public or unsecured networks. With a variety of customizable options, OpenConnect stands as a robust tool for system administrators and users needing encrypted tunnel access to networks.

Use case 1: Connect to a server

Code:

openconnect vpn.example.org

Motivation:

This is the most straightforward use of the OpenConnect command. By executing this command, users can establish a secure connection to a VPN server with minimal effort. This form of connection is particularly useful for users who are not attempting any complex configuration and just want to quickly access resources over a secure channel.

Explanation:

• openconnect: This is the command being executed, indicating the start of the VPN client.
• vpn.example.org: This is the address of the VPN server you wish to connect to. You replace it with the actual server you want to access.

Example Output:

POST https://vpn.example.org/
Attempting to connect to ... with certificate ...
Connected to HTTPS on vpn.example.org (x.x.x.x)
XML POST enabled
Please enter your username and password

Use case 2: Connect to a server, forking into the background

Code:

openconnect --background vpn.example.org

Motivation:

This use case is essential when you need the VPN to run continuously while you perform other tasks in the terminal. By forking the connection into the background, you can efficiently multitask without the VPN session occupying your active terminal window. It improves productivity by allowing you to begin work on new terminal tasks without having to open a new terminal window.

Explanation:

• openconnect: Begins the connection process.
• --background: This option tells OpenConnect to run in the background, freeing up the terminal for other tasks.
• vpn.example.org: The destination VPN server you wish to connect to.

Example Output:

Established VPN session to vpn.example.org; VDID=xxx; PID=xxxx
VPN connection established in the background

Use case 3: Terminate the connection that is running in the background

Code:

killall -SIGINT openconnect

Motivation:

At times, you may need to disconnect from a VPN session that was initiated in the background. For instance, after finishing remote tasks or needing to switch between networks, terminating the VPN session ensures security protocols are upheld by not leaving unnecessary open connections. It allows for tidy session management and helps conserve bandwidth.

Explanation:

• killall: A command-line utility used to terminate all instances of a specified command or process.
• -SIGINT: This sends an interrupt signal to terminate the process gracefully.
• openconnect: This specifies that you want to terminate all processes related to OpenConnect.

Example Output:

Terminating all instances of openconnect
VPN session ended gracefully for VPN connections

Use case 4: Connect to a server, reading options from a configuration file

Code:

openconnect --config=path/to/file vpn.example.org

Motivation:

Using a configuration file is beneficial for users who require consistent settings or configurations when connecting to a VPN. For example, system administrators or users who connect to the same VPNs regularly can save time by not having to re-enter specific options every time they initiate a connection. This also reduces the risk of human error in entering repetitive command options.

Explanation:

• openconnect: Initiates the VPN connection.
• --config=path/to/file: Specifies that OpenConnect should read additional options from a configuration file located at a specific path.
• vpn.example.org: The VPN server you intend to connect to.

Example Output:

Reading configuration from path/to/file
Connected to vpn.example.org using settings from configuration file
Please enter your username and password

Use case 5: Connect to a server and authenticate with a specific SSL client certificate

Code:

openconnect --certificate=path/to/file vpn.example.org

Motivation:

For enhanced security, some VPNs require authentication using an SSL client certificate. This method is vital for organizations that manage sensitive or classified data, ensuring that only approved devices can establish VPN connections. This use case demonstrates how OpenConnect can be used to meet such high-security standards.

Explanation:

• openconnect: The command to connect to a VPN.
• --certificate=path/to/file: This specifies the path to the SSL client certificate file necessary for authentication.
• vpn.example.org: The target VPN server for connection.

Example Output:

Certificate: path/to/file found and used for authentication
POST https://vpn.example.org/
Connected with client certificate
Please enter your username and password

Conclusion:

OpenConnect serves as a powerful and flexible VPN client, suitable for a variety of use cases and network environments. Whether it’s for basic, secure VPN access or sophisticated, configuration-savvy setups, the command’s versatility and user-friendly nature make it indispensable for anyone needing a secure network connection. By following the examples provided, users can effectively utilize OpenConnect to maintain their online security and privacy.