Telnet 1521 Port connection failure problem, after four days of efforts to finally solve!

1 since the installation of Oracle, the installation plsql are automatically detect the ORCL instance of IP and its port, the recent sudden discovery Plsql not connected, and then try Telnet 1521 port, and then found the port connection failed problem. After several groping, solved the problem.

2 Note: The installation of the ORACLE11G,12C version, Listener.ora listening to the file, did not automatically add a red circle inside the sid_name settings, this need to pay attention to check the configuration.

3 environment variable configuration, also very important, this is my local configuration, integral

(1) oracle_home:d:\app\yangtao\product\12.1.0\dbhome_2

(2) ORACLE_SID:ORCL (instance name)

(3) Path:d:\app\yangtao\product\12.1.0\dbhome_2\bin

(4) Tns_admin:d:\app\yangtao\product\12.1.0\dbhome_2\network\admin

4 Final Check Tnsnames.ora file, this is relatively simple