故障分析：用tnsping检查一下，发现可以ping通，这是因为tnsping只检查IP地址和端口是否能连通，至于数据库实例状态，监听注册了哪些服务这些，它是不检查的。
我们看一下本地数据库TNSNAMES的配置：
TESTRAC =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.58.12.124)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.58.12.125)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = 10.58.12.124)
(FAILOVER_MODE =
(TYPE = SELECT)
(METHOD = BASIC)
(RETRIES = 180)
(DELAY = 5)
)
)
设置之后，再次尝试连接数据库：
SQL> conn sys/ted@123e@prodb as sysdba;
Connected.
SQL> conn sys/ted@789e@prodb as sysdba;
Connected.
修改之后，没有再次出现同样的错误。
我们也可以通过只修改客户端hosts文件的方式，来解决这个问题。
首先在linux主机上修改HOSTS文件
root@prodb1 # vi /etc/hosts
#
10.58.12.120 prodb1-public # Public
10.58.12.124 prodb1 # Virtual
23.23.23.120 prodb1-priv # Private
10.58.12.121 prodb2-public # Public
10.58.12.125 prodb2 # Virtual
23.23.23.121 prodb2-priv # Private
10.58.12.126 prodb-scan # SCAN