Interoperability Behaviour When Using RDC and VNC on the Same Host

RDC and VNC are competing remote desktop technologies. RDC (Remote Desktop Client) uses the Remote Desktop Protocol (RDP) and VNC uses the Remote Frame Buffer (RFB) protocol. RDP is proprietary and owned by MSFT whereas RFB is open source. There are some behavioral differences that need to be taken into account when trying to use both against the same Windows host -
  • Windows desktops only allow a single interactive session, irrespective of whether you are using RDC or VNC
  • You cannot have more than one RDC session against a Windows Desktop host (you are allowed 2 user sessions and one admin session on a Windows Server)
  • You are not allowed more than one interactive VNC session against a Windows host
  • If you have an RDC session open against a Windows desktop and initiate an interactive VNC session against the same host, you will be presented with a Windows login in the VNC client. If you logon successfully, the RDC session will be terminated and the VNC session will have control of the box
  • If you have an active interactive session over VNC and you login using RDC, RDC will prompt you for the Windows password. If you successfully login, the VNC interactive session will be locked out and the VNC client will see a login screen while the RDC session has control of the desktop
  • If you login to an interactive session using VNC, you can launch other non-interactive VNC sessions that will be able to see the full desktop and any activity that is happening on the desktop.
  • You can open multiple read-only VNC sessions to the same desktop
  • You can open multiple read-write (interactive) sessions to the same desktop using VNC but this is not recommended as it could lead to a catastrophic failure if the mouse clicks and key strokes are delivered out of sequence
  • If you are log in using the VNC interactive client, all read-only screens will show the desktop. However if the screen gets locked (default behaviour), any new read-only screens will only display the password-locked screen. So password lock needs to be disabled.
  • RDC sessions on Windows desktops are not shareable. You can only have interactive RDC sessions.

The recommendation is to only use a single remote desktop technology exclusively, whether it is RDC or VNC. Using both at the same time may lead to unpredictable behavior.

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