Diagnose Oracle Database

1. Is the listener resolvable? C:\>tnsping IP:port/service(Confirms: the database listener is running on serverside)
2. Is there a firewall issue? C:\>telnet hostdb port
3. Can I login? C:\>sqlplus system/pass@MYDB or C:\>sqlplus system/pass@hostname:1521/MYDB(Confirms: The database is open)
4. Finally, chances of having a successful login with your favorite dev-tool has increased by 100%

To be able to Telnet the host you need to go to control panel, programs and add services/functionalities then telnet client.

When using Windows Telnet if the request is succesful then it won't display anything, if the request fails it will send the failure message.