From metalink (Note:220970.1).
Why do we have 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.
This means that when the client issues SQL to the node that is now down, or traverses the address list while connecting, rather than waiting on a very long TCP/IP time-out (~10 minutes), the client receives a TCP reset. In the case of SQL, this is ORA-3113. In the case of connect, the next address in tnsnames is used.
Going one step further is making use of Transparent Application Failover (TAF). With TAF successfully configured, it is possible to completely avoid ORA-3113 errors alltogether! TAF will be discussed in more detail in the section "Transparent Application Failover - (TAF)".
Without using VIPs, clients connected to a node that died will often wait a 10 minute TCP timeout period before getting an error. As a result, you don't really have a good HA solution without using VIPs.
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