1- In VNC like when one person remotely connects to a server, the one who is physically present near the server and is operating it from there doesn't get logged out. This I know. But can multiple people remotely connect via VNC? Also when it comes to other remote access methods, can we make multiple remote simultaneous connections to a single server/device?
Yes, VNC can be setup to use multiple connections, typically configured through an
"Expert” or “Advanced” tab.
2 - While using SSH & Telnet, when we remotely make a connection to a server, does the person who is physically present near the server and operating it gets logged out as well?
SSH, is typically used in Unix/Linux-based systems and allows for multi-session support, the same way Unix/Linux supports the kernel/shell architecture allowing for multiuser connections to a single machine.
As far as SSH allowing multiple connections to a single connectivity device simultaneously, this is not a good idea and should be avoided. Telnet as well allows for multiple connections; however this scenario can cause configuration issues.
3 - In terms of security, RDP is more secure or SSH?
Both SSH and RDP are secure, however nothing is 100% secure.
SSH uses keys that need to be generated and maintained, so it can add a little bit of complexity to the setup, however keys are generally more secure that password strings which is the default in RDP as well as using a well-known port.
RDP requires MFA additions to strengthen the security, uses a port in the registered port range that requires additional firewall configuration (host-based and network-based). RDP will also require at least a port forwarding rule, however this is not scalable and for large environments will require an RDP Gateway. RDP is a Windows-based technology that does not require the end-user to have a high degree of technical knowledge to use. SSH is great for Unix/Linux-based and connectivity devices using a terminal interface.