The Ecessa appliance can delegate authority for a subdomain by adding NS records in the parent zone.
In this example, the parent zone is example.com and the subdomain is sub.example.com. The authoritative name servers for this subdomain will be ns1.example.org and ns2.example.org.
In this case, since the name servers are from a different domain, no other changes are required.
If using name servers inside the domain/subdomain - for example, ns1.sub.example.com and ns2.sub.example.com - then A records should be created in the parent zone for these servers.