OS版本：rhel5.7
DB版本：RAC 11.2.0.3.0

VIP:192.168.100.33/34
SCAN-IP：192.168.100.35

ifconfig查看SCAN-IP在2节点上

orcl_01 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.100.35)(PORT = 1521))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SID = orcl2)
)
)

orcl_02 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.100.35)(PORT = 1521))
)
(CONNECT_DATA =
(SERVER_NAME = orcl)
)
)

请问大家，上面两种连接字符串，第一种orcl_01通过PL/SQL可以正常连接，第二种orcl_02却报错TNS:连接超时，这是什么原理呢？
另外，在PL/SQL的数据库连接输入：192.168.100.35:1521/orcl2报错"ORA-12514:监听程序当前无法识别连接描述符中请求的服务"？
在PL/SQL的数据库连接输入：192.168.100.35:1521/orcl2报错"TNS连接超时"。