Oracle Grid Infrastructure requires 2 network interfaces:

• Public
• Private

The public interface should host the following IPs:

1. Public Host IP
2. Node VIP
3. SCAN VIP
4. APP VIP
5. GNS VIP
6. and Others

While the Private interface hosts only 1 IP, BUT it there can be many private interfaces grouped under HAIP

The following configuration can be used for: Public Interface: eth0

[root@lparacb ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0 
DEVICE=eth0
HWADDR=08:00:27:70:D3:B7
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.100.20
NETMASK=255.255.255.0
PEERDNS=no
[root@lparacb ~]# 

The following configuration can be used for: Private Interface: eth1

[root@lparacb ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth1 
DEVICE=eth1
HWADDR=08:00:27:C5:75:A7
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=static
IPADDR=10.0.2.20
NETMASK=255.255.255.0
PEERDNS=no
[root@lparacb ~]# 

PEERDNS is important otherwise you will inherit the DNS from the base system