An NIS domain is a collection of machines that 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. Domain names are case-sensitive.
Any machine can belong to a given domain, as long as there is a server for that domain's maps in the same network. Solaris Release 2 machines do not require the server to be on the same subnet, but earlier implementations of NIS historically have required that a server exist on every subnet using NIS. A NIS client machine obtains its domain name and binds to a NIS server as part of its boot process.