Network Practices - Expert Oracle RAC 12c - page 268

many RAC clusters, each cluster with many nodes, numerous DNS entries must be configured.
For example, a six-node cluster requires 2 x 6 + 3 = 15 entries, and ten such clusters require 150 entries. As the number of
cluster databases and the total number of nodes increase, the DNS methods became less manageable. For this reason,
Oracle 11gR2 Clusterware introduced the second method called GNS.

Name Resolution Using GNS
GNS provides name resolution for VIPs based on DHCP (Dynamic Host Configuration Protocol). In this method, GNS
provides dynamic IP addresses for the virtual hostnames of all the nodes and SCAN in the cluster, through the DHCP
service. In GNS, the only GNS VIP is given a static IP, and this static GNS VIP is registered in DNS. The GNS method
use the subdomain delegation, DNS forwards any network name request on a particular subdomain to the GNS
server, and the GNS will provide the name resolution to the dynamic IP. GNS uses multicast Domain Name Server
(mDNS) in the Oracle Clusterware to provide a DHCP IP address mapping to the VIP name. The benefit of GNS is the
simplification of SCAN VIPs and node VIPs by moving the management of these VIPs from DNS to the GNS local to
the cluster. With GNS, adding or deleting a node is even simpler than with the DNS method, as there is no change in
DNS when you add or delete a node.
Here, we use the knewrac cluster as an example to illustrate how GNS name resolution works (Figure 9-10 ) and
the steps to configure it.

subdomain: kcloud.dblab.com

gns.grid.dblab.com Assign VIP addresses by DHCP:

SCAN VIP: knewrac-scan:
172.16.150.40
172.16.150.83
172.16.150.28

GNS service
gns.kcloud.dblb.com
Node 1:knewracn1

DN Sserver: 172.16.15.55
Register GNS VIP:
gns.kcloud.dblab.com IN A 172.16.15.9

Node 2: knewracn2

Register GNS subdoman deligation:
kcloud.dblab.com NS gns.kcloud.dblab.com

Virtual Ips of RAC nodes:
172.16.150.37 for knewracn1-vip
172.16.150.182 for knewracn2-vip
172.16.150.199 for knewracn3-vip

Node 3: knewracn3

Figure 9-10. Name resolution using GNS

This cluster uses the subdomain kcloud.dblab.com . In DNS, two entries are requested:

the static IP address of GNS VIP: 172.16.15.9
the subdomain deligagtion:

•

•

subdomain kcloud.dblab.com to GNS server gns.kcloud.dblab.com

With the proceeding setup, any host request in the domain “ *.kblod.dblab.com ” , for example,
knewrac-scan.kclod.dblab.com , will be handed off to the GNS server: gns.kcloud.dblab.com with VIP address
172.16.15.9. This GNS server maps the VIP name knewrac-scan.kclod.dblab.com to one of the three SCAN VIPs:
172.16.150.40, 172.16.150.83, or 172.16.150.28.