The tnsnames.ora file has an entry for the service alias ORCL as follows:
ORCL =
( DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.156.24.216)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl.oracle.com)
) )
The TNSPING command executes successfully when tested with ORCL, but you are not able to connect to the database instance with the following command:
SQL> CONNECT scott/tiger@orcl
What could be the reason for this?
A.The listener is not running on the database node.
B.The TNS_ADMIN environmental variable is set to a wrong value.
C.The orcl.oracle.com database service is not registered with the listener.
D.The DEFAULT_DOMAIN parameter is set to a wrong value in the sqlnet.ora file.
如果 listener 没有启动，则 tnsping 不会成功，所以 A 错
TNS_ADMIN 主要应用于一台主机上有多个版本的数据库，指定文件的路径，所以 B 错
当 SERVICE_NAME 填写不正确时，你可以 tnsping 通数据库实例，但是却无法连接到数据库实例，因为你填写错的SERVICE_NAME 并没有注册到 LISTENER 当中，C 正确
DEFAULT_DOMAIN 主要是设定客户端解析名字的域 ，D 错误