An NIS domain is a collection of hosts which share a common set of NIS maps. Each domain has a domain name, and each machine sharing the common set of maps belongs to that domain.
NIS domains and DNS domains are not necessarily the same. In some environments, NIS domains are defined based on enterprise-wide network subnet administrative layouts. DNS names and domains are defined by internet DNS naming standards and hierarchies. The two naming domain naming systems might be or might not be configured to match up identically. The domain name for the two services are controlled separately and might be configured differently.
Any host can belong to a given domain, as long as there is a server for that domain's maps in the same network or subnet. NIS domain lookups use remote procedure calls (RPCs). Therefore, NIS requires that all the clients and all the server machines that provide direct services to those clients must exist on the same accessible subnet. It is not uncommon to have each administrative subnet managed as a separate NIS domain (distinct from an enterprise-wide DNS domain) but using common databases managed from a common master machine. The NIS domain name and all the shared NIS configuration information is managed by the svc:/network/nis/domain SMF service.