How to use the command openconnect (with examples)
Openconnect is a VPN client that allows users to connect to Cisco AnyConnect VPNs and other types of VPN servers. It provides a secure, encrypted connection between the client and the server, ensuring privacy and data integrity.
Use case 1: Connect to a server
Code:
openconnect vpn.example.org
Motivation: The motivation for using this example is to establish a connection to a VPN server located at “vpn.example.org”. By using the “openconnect” command followed by the server’s address, the user can connect to the server and access resources within the VPN network.
Explanation: The command “openconnect vpn.example.org” initiates a connection to the specified server. The “vpn.example.org” argument denotes the address of the server to connect to.
Example output:
POST https://vpn.example.org/auth [vpn.example.org]
Got CONNECT response: HTTP/1.1 200 OK
CSTP connected. DPD 30, Keepalive 32400
Connected as 192.168.1.100, using SSL
Use case 2: Connect to a server, forking into the background
Code:
openconnect --background vpn.example.org
Motivation: This example is useful when the user wants to connect to a VPN server without blocking the terminal. By using the “–background” option, the “openconnect” command forks into the background, allowing the user to continue using the terminal for other tasks.
Explanation: The command “openconnect –background vpn.example.org” initiates a connection to the specified server and forks the process into the background. The “–background” option ensures that the command does not occupy the terminal.
Example output: This example does not produce any output in the terminal. The connection is established in the background.
Use case 3: Terminate the connection that is running in the background
Code:
killall -SIGINT openconnect
Motivation: This use case is applicable when the user wants to terminate a background connection that was established using the “openconnect” command with the “–background” option. By using the “killall -SIGINT openconnect” command, the user can send an interrupt signal to the process and terminate the connection.
Explanation: The command “killall -SIGINT openconnect” sends an interrupt signal (-SIGINT) to all processes with the name “openconnect”, effectively terminating the background connection.
Example output: This command does not produce any output. It terminates the background connection without displaying any messages.
Use case 4: Connect to a server, reading options from a config file
Code:
openconnect --config=path/to/file vpn.example.org
Motivation: When connecting to a server, there might be multiple options and configurations to specify. By using a config file, the user can store these options in a file and easily provide them to the “openconnect” command. This example demonstrates how to read options from a config file.
Explanation: The command “openconnect –config=path/to/file vpn.example.org” starts a connection to the specified server using the options specified in the given configuration file. The “–config=path/to/file” argument indicates the path to the configuration file to be used.
Example output:
POST https://vpn.example.org/auth [vpn.example.org]
Got CONNECT response: HTTP/1.1 200 OK
CSTP connected. DPD 30, Keepalive 32400
Connected as 192.168.1.100, using SSL
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: This example is useful when the VPN server requires client certificate authentication. By using the “–certificate=path/to/file” option, the user can provide the path to their client SSL certificate and authenticate with the server.
Explanation: The command “openconnect –certificate=path/to/file vpn.example.org” connects to the specified server and authenticates using the SSL client certificate located at the given file path. The “–certificate=path/to/file” argument indicates the path to the client SSL certificate.
Example output:
POST https://vpn.example.org/auth [vpn.example.org]
Got CONNECT response: HTTP/1.1 200 OK
CSTP connected. DPD 30, Keepalive 32400
Connected as 192.168.1.100, using SSL and client certificate
Conclusion:
The “openconnect” command is a versatile VPN client that offers various options for connecting to VPN servers. By utilizing its different use cases, users can establish secure connections, customize configurations, and authenticate with servers using client certificates. These examples provide a clear understanding of how to use the “openconnect” command and its options in different scenarios.
