Telnet to determine whether the port is open

Use Telnet IP port number to view port opening, how to judge by return value?

If the port is open, go directly to the port.

Enter the Telnet IP port number in cmd, and there will be two return results.

One is: connected to (IP) ... Unable to open connection to host, port number: Connection failed
This is a return result that is not open for this IP port

The other opens a new CDM window and closes the original window, which indicates that the IP window is open

Telnet up if the interface is dark, see the cursor flashing, indicating that the port is open.

Test

Requirements: The remote server runs a service on a port and needs to test to determine if the service exists.

Telnet command If only IP is specified, the default is connected to port 23 on the end-to-end.

If a port is specified, connect to the corresponding port.

The Telnet IP port command can be used to test whether a port on a server is open.

Like what:

C:/users/administrator>telnet www.baidu.com 80

If the port is open, you will see a blank screen indicating that the connection was successful.

Otherwise, the connection failure is prompted.

C:/users/administrator>telnet www.111cn.net 80666
Connecting www.111cn.net ... The connection to the host could not be opened. On port 80666: Connection Failed