I don’t really understand the purpose of GNS and how to configure it. If I understand this article good I need to have let’s say 3 PCs.

dns.example.com eth0 192.168.10.250/24
rac1.example.com eth0 192.168.10.1/24 eth1 192.168.192.1/24
rac2.example.com eth0 192.168.10.2/24 eth1 192.168.192.2/24

On the dns.example.com I create my DNS configuration as for a standard cluster.

rac1  192.168.10.1
rac1-priv 192.168.192.1
rac2 192.168.10.2
rac2-priv 192.168.192.2

and

gns.example.com 192.168.10.100

in the resolv.conf

options attempts: 2
options timeout: 1

search example.com
nameserver 192.168.10.250
nameserver 192.168.10.100

and after I have setup this it should be possible to create a Grid installation with GNS?
if the answer is no, why do I need a subdomain?

Edit:
https://gjilevski.com/2010/09/05/gns-configuration-for-oracle-11gr2-in-dns-using-dhcp/