The Oracle Grid Naming Service (GNS) is used with large clusters to ease network administration cost.

For small clusters, you can use a static configuration of IP addresses. For large clusters, manually maintaining the large number of required IP addresses becomes too cumbersome.

• About Oracle Grid Infrastructure Name Resolution Options
  Before starting the installation, you must have at least two interfaces configured on each node: One for the private IP address and one for the public IP address.
• Cluster Name and SCAN Requirements
  Review this information before you select the cluster name and SCAN.
• IP Name and Address Requirements For Grid Naming Service (GNS)
  The network administration must configure the domain name server (DNS) to delegate resolution requests for cluster names (any names in the subdomain delegated to the cluster) to the GNS.
• IP Name and Address Requirements For Multi-Cluster GNS
  Multi-cluster GNS differs from standard GNS in that Multi-cluster GNS provides a single networking service across a set of clusters, rather than a networking service for a single cluster.
• IP Address Requirements for Manual Configuration
  If you do not enable GNS, then the public and VIP addresses for each node must be static IP addresses. Public, VIP and SCAN addresses must be on the same subnet.
• Confirming the DNS Configuration for SCAN
  You can use the nslookup command to confirm that the DNS is correctly associating the SCAN with the addresses.
• Grid Naming Service for a Traditional Cluster Configuration Example
  To use GNS, you must specify a static IP address for the GNS VIP address, and you must have a subdomain configured on your domain name servers (DNS) to delegate resolution for that subdomain to the static GNS IP address.
• Domain Delegation to Grid Naming Service
  If you are configuring Grid Naming Service (GNS) for a standard cluster, then before installing Oracle Grid Infrastructure you must configure DNS to send to GNS any name resolution requests for the subdomain served by GNS.
• Manual IP Address Configuration Example
  If you choose not to use GNS, then before installation you must configure public, virtual, and private IP addresses. Also, check that the default gateway can be accessed by a ping command.