There are three phases for changing IP addresses of an Oracle Cluster related to three groups of networks used; public, VIP and SCAN. Below you may find the steps to alter IP addresses of a 11g RAC installation running on Oracle Linux 5. Be sure you follow the steps in order because changes for public network should be done before VIP network changes.

Changing Public IPs

1. Check current network information:
$ $GRID_HOME/bin/oifcfg getif
eth0  10.10.11.0   global   public
eth1  192.168.0.0   global   cluster_interconnect

2. Delete the existing interface information from OCR
$ $GRID_HOME/bin/oifcfg delif -global eth0/10.10.11.0

3. Add it back with the correct information
$ $GRID_HOME/bin/oifcfg setif -global eth0/10.10.12.0:public

4. Shutdown the cluster
$ crsctl stop cluster -all

5. Modify the IP address at network layer, DNS and /etc/hosts file to reflect the change. Files to modify/check are:
   - /etc/sysconfig/network-script/ifcfg-eth0
   - /etc/sysconfig/network
   - /etc/hosts

Restart network interface to activate changes
$ ifdown eth0
$ ifup eth0

6. Restart the cluster
$ crsctl start cluster -all

Changing VIPs

1. Check current configuration
$ srvctl config nodeapps -a
Network exists: 1/10.10.11.0/255.255.255.0/eth0, type static
VIP exists: /racnode1-vip/10.10.12.11/10.10.12.1/255.255.255.0/eth0, hosting node racnode1
VIP exists: /racnode2-vip/10.10.12.12/10.10.12.1/255.255.255.0/eth0, hosting node racnode2

2. Stop the database instance and VIP:
$ srvctl stop instance -d <db_name> -n racnode1
$ srvctl stop vip -n racnode1 -f

3. Ensure VIP is offline and VIP is not bounded to network interface
$ crsctl stat res -t
$ ifconfig -a

4. Modify the IP address at network layer, DNS and /etc/hosts file to reflect the change

5. Alter the VIP
$ srvctl modify nodeapps -n racnode1 -A 10.10.12.12/255.255.255.0/eth0

6. Verify the change
$ srvctl config nodeapps -n racnode1 -a
VIP exists.: /racnode1-vip/10.10.12.12/255.255.255.0/eth0 hosting node racnode1

7. Start the database instance and VIP
$ srvctl start vip -n racnode1
$ srvctl start instance -d <db_name> -n racnode1

8. Ensure VIP is online and VIP is bounded to network interface
$ crsctl stat res -t
$ ifconfig -a

9. Repeat the steps above for the other nodes in the cluster

Changing SCAN IPs

1. Update DNS with the new IP addresses. If host file is used, change IP in the host file.

2. Stop the SCAN listener and the SCAN
$ $GRID_HOME/bin/srvctl stop scan_listener
$ $GRID_HOME/bin/srvctl stop scan
$ $GRID_HOME/bin/srvctl status scan

3. Check the current IP address(es) of the SCAN
$ $GRID_HOME/bin/srvctl config scan
SCAN name: <scan_name>, Network: 1/10.10.12.0/255.255.255.0/eth0
SCAN VIP name: scan1, IP: /<scan_name>/10.10.11.15

4. Refresh the SCAN with the new IP addresses from the DNS entry:
$ $GRID_HOME/bin/srvctl modify scan -n <scan_name>

5. Check whether the SCAN has been changed
$GRID_HOME/bin/srvctl config scan
SCAN name: <scan_name>, Network: 1/10.10.12.0/255.255.255.0/eth0
SCAN VIP name: scan1, IP: /<scan_name>/10.10.12.15

You can refer to documents; [ID 276434.1] for public and VIP network changes and [ID 952903.1] for SCAN IP changes for detailed information.