An IP address with an associated network name registered in the domain name service (DNS) for the public interface. If you do not have an available DNS, then record the network name and IP address in the system hosts file, /etc/hosts.

One virtual IP (VIP) address with an associated network name registered in DNS. If you do not have an available DNS, then record the network name and VIP address in the system hosts file, /etc/hosts. Select an address for your VIP that meets the following requirements:

• The IP address and network name are currently unused

• The VIP is on the same subnet as your public interface

Before installation, check that the default gateway can be accessed by a ping command. During installation, OUI uses the ping command to ensure that the VIP is reachable. To find the default gateway, use the route command, as described in your operating system's help utility. After installation, configure clients to use either the VIP address, or the network name associated with the VIP. If a node fails, then the node's virtual IP address fails over to another node.

A private IP address with a host name for each private interface

Oracle recommends that you use private network IP addresses for these interfaces (for example: 10.*.*.* or 192.168.*.*). Use the /etc/hosts file on each node to associate private network names with private IP addresses.

VIP特点：
1 VIP是在clusterware安装最后阶段，通过脚本VIPCA创建的；
2 VIP作为一个Nodeapps类型的CRS Resource注册到OCR中，并由CRS维护状态；
3 VIP会绑定到节点的public 网卡上；那么public网卡就有两个地址了；
4 当某个节点发生故障时，CRS会把故障节点的VIP转移到其他节点上；
5 每个节点的Listener会同时在public网卡的public IP和VIP两个地址上监听；
6 客户端的tnsname.ora一般会配置指向节点的VIP；

public    公共IP地址，对外提供服务的IP。
private   私有IP地址，RAC内部之间通信。
vip       虚拟IP地址，用于网络出现故障时进行IP地址漂移。