From HEXONET Wiki
The following are information relating to HEXONET's DNS Service, including how to create and manage DNS zone, using HEXONET's DNS with your domain and DNSSEC support. To learn more about Premium DNS, go to Premium DNS
DNS Service Restrictions
Basic DNS is available only for domains that are registered with HEXONET.
However, Basic DNS is not available for subdomains even if the parent domain is registered with HEXONET. To create a DNS zone for subdomains, it must be created with Premium DNS.
Premium DNS is available for any domain names, regardless if it is registered with HEXONET or not.