BIP 11 clustering

Hi,

We are trying to set up BIP clustering. For that we followed below steps,

1.   we have installed BIP in Server1.

2. In the second server installed BIP by using "Scale out BI" system option.

3. We are using only BIP component in OBIEE,to do cluster, we followed the steps given in "http://docs.oracle.com/cd/E21764_01/doc.1111/e15722/bi_clusters.htm

4. After following above steps , can see bi_server2 aswell. But here how we can see that when one server goes down how come BI publisher will be up and running and execute reports on other side.. For this clustering, do we need to use any virtual IP.