Let’s go over Oracle VIP.
At times, in the cluster configuration, SharePlex uses Oracle VIP instead of host clustering VIP.
Why is the Virtual IP necessary in Oracle RAC Environment?
That is because of client(Application) TCP timeouts.
Let’s have a look on diagram.
Here, VIP#1 is up in Node1 and VIP#2 is up in Node2. And, each VIP is mapped to the Ethernet device eth0.
Client is connected through the Listener.
In case of Node1 is shutdown for some reason, VIP#1 moved to Node2 and mapped to eth0:1.
Here, the thing is that VIP#1 is not linked to LISTENER, it is just UP in Node2.
At this point, Client got acknowledged that the connection to VIP#1 is disconnected.
Without this kind of acknowledgement from VIP#1, client should wait until TCP timeout value, it is normally 200s.
It means that for 200s, Client should be stuck.
However, now Client knows that connection is lost, so it can try to reconnect to available node, finally it is connected to VIP#2.
This is how Oracle VIP works and the reason we need it in the cluster environment.