This depends on the router but I wouldn't normally (except for on a high end router) expect it to be more than 1. I would recommend looking at the manufacturers website or manual.
two
The number of simultaneous Telnet sessions a switch can open typically depends on the specific model and its configuration. Many switches support between 5 to 16 concurrent Telnet sessions by default, but this can often be adjusted in the switch's settings. It's important to check the switch's documentation for precise limits and capabilities. Additionally, network performance and management considerations should be taken into account when configuring these sessions.
The router can handle as many telnet sessions as there are VTYs. The maximum number of possible VTYs varies by platform. There are 5 VTYs by default, you can add more VTYs by configuring them in configuration mode. Example Line vty 0 16 login (or any command) Once you refer to a VTY, it will be created.
Because the telnet session is in clear text and programs can capture the passwords to log in to telnet sessions.
Telnet operates over TCP Port 23.
show sessions
Show sessions command
port 23
for
TCP has no default port. Individual applications - such as FTP, DNS, or Telnet - do have default ports.
No, it does not.
In order to be able to telnet to a computer, it has to be running a telnet daemon or service. Windows XP does not run such a service by default. It can be activated (in the Professional version at least) in the Services console.