For security reasons, access to your Lorentz workstation is only possible within the Lorentz Institute intranet. Remote access can occur either securing your connection via an intermediate step called SSH tunneling (AKA port forwarding), through the Lorentz Institute VPN service or via the Lorentz Institute Remote Workspace.

Following are some examples that demonstrate the concept of SSH tunnelling. For alternative methods of connection, please see the relevant documentation.

The examples below have been tested with OpenSSH v7.3+.

By means of an SSH tunnel you can transport any arbitrary data over an encrypted SSH connection. Members of the Lorentz Institute can use this technique to gain remote shell access to their workstation across our firewall which would prevent access otherwise.

For remote ssh connections to your IL workstation, the steps above can be summarised into the following. Establish an ssh client-server to our SSH server and instruct your SSH client to forward any new SSH-connection data that will be sent to an arbitrary port number to go via our SSH server. The server will then relay this information to the SSH server running on your workstation.

Establish an SSH connection to workstation.lorentz.leidenuniv.nl via our SSH server styx.lorentz.leidenuniv.nl

ssh -o ProxyCommand="ssh -W %h:%p username@styx.lorentz.leidenuniv.nl" username@workstation.lorentz.leidenuniv.nl

For connections that will use the DISPLAY environment variable (think of any application with a GUI), add the option -X to your SSH commands.

As in Example 1 but this time using your client ssh configuration file usually located at $HOME/.ssh/config on GNU/Linux systems

# cat $HOME/.ssh/config
Host workstation.lorentz.leidenuniv.nl workstation
     ProxyCommand /usr/bin/ssh -W %h:%p styx.lorentz.leidenuniv.nl
     User username

Once this configuration is in place, a simple ssh workstation will get you to your workstation.

Establish a web browser connection to a jupyter notebook on workstation.lorentz.leidenuniv.nl port YYYY.

Configure your local $HOME/.ssh/config as below

Host styx
   HostName styx.lorentz.leidenuniv.nl
   LocalForward YYYY localhost:YYYY
 
Host workstation
   HostName workstation.lorentz.leidenuniv.nl
   ProxyJump styx
   LocalForward YYYY localhost:YYYY

Browse to http://localhost:YYYY.

Establish a web browser connection to a Jupyter Notebook session running on node marisXX when outside the IL intranet ¹⁾

Host lorentz
     HostName ssh.lorentz.leidenuniv.nl
     User username

Host maris
     HostName xmaris.lorentz.leidenuniv.nl
     ProxyJump lorentz
     User username

Host marisXX
     HostName marisXX.lorentz.leidenuniv.nl
     ProxyJump maris
     User username
     LocalForward YYYY localhost:YYYY

Browse to http://localhost:YYYY.

In the snapshots that follow, please replace all occurrences of novamaris with xmaris.

You will need to open two putty sessions. The first one opens a tunnel, the second one uses it. For the sake of clarity let us call the first session `Tunnel' and the second one `Tunnel_use'. In this example we will establish a connection to the Maris headnode novamaris through an ssh tunnel on ssh.lorentz.leidenuniv.nl.

Open putty and create a session called Tunnel, then set it according to the snapshots below

Please note the settings in the port forwarding panel. We use an arbitrary port (2222), but you can choose any numbers above 1024 provided they are not currently in use. By pushing `Open', a terminal will appear so that you can authenticate using your Lorentz institute credentials. Leave this terminal open and proceed with the creation of session `Tunnel_use'

Now push `Open' and a terminal will appear asking your authentication credentials on novamaris. Any other putty connection to localhost:2222 will ssh directly to novamaris.

For detailed instructions on how to set up a vnc session you are encouraged to follow these instructions.

Finally, take a look at x2go should you be interested.

Please read here.

Read here