【求助】oracle 11G 自动建立的实例名称无法使用

Question

近期在redhat linux 5.8 oracle 11.2.0.4.0 上创建实例，创建完后发现无法使用实例名登陆，尝试着手动建立一个仅是把服务名改了，就可以正常登陆了，很无语，请各位大侠帮忙分析一下，谢谢！
自动建立的tnsnames.ora 中配置：

SYSIT =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.12)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sysit)
)
)

尝试使用：
sqlplus admin/admin12@sysit
QL*Plus: Release 11.2.0.4.0 Production on Mon Aug 24 14:05:55 2015

Copyright (c) 1982, 2013, Oracle. All rights reserved.

ERROR:
ORA-12504: TNS:listener was not given the SERVICE_NAME in CONNECT_DATA
Enter user-name:

手动复制后改完服务名后：
ISYSIT =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.12)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sysit)
)
)

尝试使用：
sqlplus admin/admin12@isysit
SQL*Plus: Release 11.2.0.4.0 Production on Mon Aug 24 14:16:52 2015

Copyright (c) 1982, 2013, Oracle. All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>

Answer 1

现在tnsnames.ora 中的配置是这样的：
SYSIT =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.12)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sysit)
)
)

ISYSIT =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.0.12)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sysit)
)
)