使用虚拟机器安装好10205版本的RAC后，使用CMD连接数据库第一次总是出现ORA-12515的问题，需要第二次连接才能连上，出现这样的问题，官方文档有这样的描述：

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Symptoms

When we try to connect to a RAC service name we sometimes get redirected by the first node's listener to the public address/hostname of the second node instead of its VIP address. An ORA-12545 error may be generated if that public hostname is not configured in DNS.

We were expecting the connection to eventually be redirected to the VIP of the other node.

Cause

The Database on one RAC node remote registers with the wrong local IP address to the listener on the other RAC node (e.g. the public IP address instead of the wanted VIP address).

The PMON process handles database registration to the local and remote listeners. For remote listeners registration PMON will have to find out what is the IP address of the local system in order to present it to the remote listener as database contact address.

In the default Oracle configuration, for hosts which have more than one IP address configured on the network interfaces, it is undefined which IP address will be selected for remote registration.

Solution

Modify the local_listener database parameter to point to the local VIP address. For the parameter value use either an alias name which contains in the DESCRIPTION field only the VIP address or use an explicit connection statement like the following:
alter system set LOCAL_LISTENER="(ADDRESS=(PROTOCOL=TCP)(HOST=)(PORT=1521))" scope=both sid='instance_name';

Where "instance_name" is the unique instance name. Issue this statement for all instances in the cluster.
The LOCAL_LISTENER database parameter will give PMON a hint in respect of which IP address it should use for remote registration with other nodes' listener(s).

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这里描述，出现这个问题主要是RAC远程注册使用了错误的IP地址，把公共的IP地址错用为VIP地址，把LOCAL_LISTENER这参数修改一下就解决了该问题。