Domains are used to organize computers. Domains are helpful in defining territories that users have access to.
A DNS (Domain Name System) is a system that resolves/translates user-friendly names (such as host names or domain names) into computer-friendly names (such as IP addresses). A DNS can be a single server on a LAN or the multitude of DNS servers distributed all over the Internet.
For my purposes, there are a few dominant kinds of domains:
- NetBIOS domains. Aka NetBEUI domain, since NetBEUI is an extension of NetBIOS.
- In a pure NetBIOS domain, computers are identified by a NetBIOS name (<= 15 bytes) and are non-routable (i.e. non-TCP/IP). No name resolution server is required.
- A flat and unstructured namespace.
- TCP/IP domains. Aka DNS domains.
- In a pure TCP/IP domain, computers are identified by an IP address and are routable. DNS names are encoded in Unicode. The type of name resolution server required is DNS (Domain Name Service).
- A hierarchical and structured namespace.
- NT domains. Aka Windows domains. Used by networks administered by a Windows NT Server.
- In a NT domain, computers are identified by both IP address and NetBIOS name. The type of name resolution servers required are DNS and WINS (Windows Internet Name Service). WINS translates between NetBIOS and DNS names.
- The flat name spaces of NetBIOS are mapped with the hierarchical namespaces of DNS domains.
- Active Directory domains. Aka W2000 domains. Used by networks administered by a Windows 2000 Server.
- In a pure W2000 domain, computers are identified by Active Directory object, IP address. A DNS is required but WINS is not.
- In a mixed W200 domain, computers are identified by Active Directory object, IP address, and NetBIOS name. A DNS and WINS are required.
- Active Directory objects mirror the DNS hierarchy but occupy separate namespaces. Both are mapped to the flat NetBIOS namespace as necessary.
Note that the left most item of a DNS name can be a computer, but the Active Directory hierarchy tree only contains domains. Note also that TLDs are outside of the Active Directory although they appear as part of a domain name. EG: