IP address uniquly define host. if you type wrong ip address you will have to wait for 1 minute (generally). In RAC env, if by any problem, one node is not present and new connect request comes, new connection has to wait for 1 minutes and will get error that host does not exists. Alternatly if we define virtual IP address, we may redirect connection to another server without wasting time.
Here is some more description from
http://www.oracle.com/technology/pub/articles/hunter_rac10gr2_iscsi.htmlAbout Virtual IP
Why is there a Virtual IP (VIP) in 10g? Why does it just return a dead connection when its primary node fails?
It's all about availability of the application. When a node fails, the VIP associated with it is supposed to be automatically failed over to some other node. When this occurs, two things happen.
The new node re-arps the world indicating a new MAC address for the address. For directly connected clients, this usually causes them to see errors on their connections to the old address.
Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.
