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These changes range from the mundane low-level services, like storage management, to esoteric services, such as the hierarchical and distributed Active Directory, which replaces the creaking LAN Manager domain model. For network designers and administrators, perhaps the most important of these technology swaps is in network naming services, with the long-reviled NetBIOS mostly being eliminated in favor of the Internet-centric DNS.

This is good news, because NetBIOS has long been a bane of administrators trying to implement Microsoft networking solutions on heterogeneous, multiplatform and multisegment networks. It's true that NetBIOS' simple design is functional for small-scale networks; features such as autonomous name-registration and broadcast-based lookups let small networks build dynamic naming tables without requiring any real administration. However, NetBIOS has never worked well in complex environments. Ask any organization with more than three distinct sites and you'll get an idea of the difficulties involved.

These shortcomings are eliminated with Windows 2000, however, because systems can now use DNS to register and locate each other on an IP network. This feature provides several benefits to network administrators. The main advantage comes from the fact that DNS is a proven, scalable and multivendor technology, while NetBIOS is none of these things. With DNS, a single network naming service can be used for different services, including Internet technologies, such as Web and mail.

DNS Is Not Enough

Before discussing how Windows 2000 uses DNS for name registration and lookup services, it's important to point out that NetBIOS names are still used by Windows 2000's core networking services. They are used as the primary identifier for a host (you can't override them with the DHCP host-name option), and as such they continue to show up in network browse lists and similar places.

What has changed is the way Windows 2000 system names and some services (Active Directory in particular) are registered and located on the network. Windows 2000 uses Dynamic DNS (as described in RFC 2136) to add and delete resource records in DNS on the fly, letting Windows 2000 systems (or a DHCP server) modify host-name-to-address mappings dynamically without using NetBIOS queries. In addition, Active Directory systems use the DNS SRV (service-location) resource record (which is described in RFC 2782) for registering and locating the special-purpose servers, such as the PDC (primary domain controller) or the catalog server.

This means that the dynamic and autonomous name-registration features that made NetBIOS useful on small networks have not been lost. Although DNS has required a significant amount of manual oversight and administration, Dynamic DNS and SRV resource records make this a nonissue. Simple networks with nothing but Windows 2000 hosts can register and locate each other dynamically without using NetBIOS, while large-scale networks of "pure" DNS systems can continue to operate smoothly.

Supporting older Microsoft OSes or NetBIOS-specific services, such as SNA gateways or backup servers, will still require a NetBIOS-over-TCP/IP naming service of some kind--broadcasts, static LMHOSTS files or WINS (Windows Internet Name Service). This means that most shops will have to run NetBIOS naming services to support their mixed-mode networks, severely limiting the functional benefits of this design. Because many applications likely will continue to support NetBIOS as a lowest-common-denominator naming service for years, it's unlikely you'll escape the need to manage and operate multiple naming services any time soon.