When I installed Oracle RAC, I have configured the SCAN Listener with Dnsmasq. it uses the hosts file located on /etc folder. My surprise was when I started working with the RAC I just have one SCAN_LISTENER. The issue with DNSmasq is that is use the /etc/hosts entry so I prefer to go ahead and configure a complete DNS (I Installed BIND on Oracle Linux 6) and now I want to update the SCAN with the other two SCAN Listeners. Please find below the procedures:

Checking the actual configuration

[root@host01 ~]# nslookup cluster01-scan.example.com
Server:         192.168.1.175
Address:        192.168.1.175#53

Name:   cluster01-scan.example.com
Address: 192.168.1.122
Name:   cluster01-scan.example.com
Address: 192.168.1.123
Name:   cluster01-scan.example.com
Address: 192.168.1.121

[root@host01 ~]# srvctl config scan
SCAN name: cluster01-scan.example.com, Network: 1/192.168.1.0/255.255.255.0/eth0
SCAN VIP name: scan1, IP: /cluster01-scan/192.168.1.121

[root@host01 ~]# srvctl config scan_listener
SCAN Listener LISTENER_SCAN1 exists. Port: TCP:1521

As you can see it is just one SCAN VIP configured, now we will stop the scan listener and scan resource and add the other two scan vips

[root@host01 ~]# srvctl stop scan_listener

[root@host01 ~]# srvctl stop scan

[root@host01 ~]# srvctl modify scan -n cluster01-scan.example.com
[root@host01 ~]# srvctl config scan
SCAN name: cluster01-scan.example.com, Network: 1/192.168.1.0/255.255.255.0/eth0
SCAN VIP name: scan1, IP: /cluster01-scan.example.com/192.168.1.123
SCAN VIP name: scan2, IP: /cluster01-scan.example.com/192.168.1.121
SCAN VIP name: scan3, IP: /cluster01-scan.example.com/192.168.1.122

updating the scan listener to match with the two Scan Vips that we added before.

[root@host01 ~]# srvctl modify scan_listener -u
[root@host01 ~]# srvctl config scan_listener
SCAN Listener LISTENER_SCAN1 exists. Port: TCP:1521
SCAN Listener LISTENER_SCAN2 exists. Port: TCP:1521
SCAN Listener LISTENER_SCAN3 exists. Port: TCP:1521

Starting SCAN Listener and checking the configuration

[root@host01 ~]# srvctl start scan_listener

[root@host01 ~]# srvctl config scan
SCAN name: cluster01-scan.example.com, Network: 1/192.168.1.0/255.255.255.0/eth0
SCAN VIP name: scan1, IP: /cluster01-scan.example.com/192.168.1.121
SCAN VIP name: scan2, IP: /cluster01-scan.example.com/192.168.1.122
SCAN VIP name: scan3, IP: /cluster01-scan.example.com/192.168.1.123

[root@host01 ~]# srvctl config scan_listener
SCAN Listener LISTENER_SCAN1 exists. Port: TCP:1521
SCAN Listener LISTENER_SCAN2 exists. Port: TCP:1521
SCAN Listener LISTENER_SCAN3 exists. Port: TCP:1521
[root@host01 ~]#

[root@host01 ~]# srvctl status scan
SCAN VIP scan1 is enabled
SCAN VIP scan1 is running on node host03
SCAN VIP scan2 is enabled
SCAN VIP scan2 is running on node host02
SCAN VIP scan3 is enabled
SCAN VIP scan3 is running on node host01

[root@host01 ~]# srvctl status scan_listener
SCAN Listener LISTENER_SCAN1 is enabled
SCAN listener LISTENER_SCAN1 is running on node host03
SCAN Listener LISTENER_SCAN2 is enabled
SCAN listener LISTENER_SCAN2 is running on node host02
SCAN Listener LISTENER_SCAN3 is enabled
SCAN listener LISTENER_SCAN3 is running on node host01