TCP/IP in Windows 2000 Professional

TCP/IP-based services use IP addresses to identify each other, but users and applications frequently require computer names for host identification. A name resolution mechanism must be available on a TCP/IP network to resolve names to IP addresses.

When a request for name-to-IP address resolution is made, the Windows 2000 resolver first submits the name query to DNS. If DNS name resolution fails, the resolver checks to see whether the name is longer than 15 bytes. If it is longer, resolution fails. If not, the resolver then checks to see if NetBIOS is running. If it is not running, resolution fails. If it is running, the resolver then tries NetBIOS name resolution.

Figure 22.2 and Figures 22.6 and 22.7 show an overview of the process.

Figure 22.2 Overview of Name Resolution

Windows 2000 Professional provides several different types of name resolution, including DNS, WINS, name resolution using Hosts or Lmhosts files, and broadcast name resolution. Generally, a Windows 2000 Professional– based computer uses a combination of these name resolution types, summarized in this section.

Domain Name System Name Resolution

The Domain Name System (DNS) is a global, distributed database based on a hierarchical naming system. DNS name resolution is used on the Internet to map friendly names to IP addresses, and vice versa. DNS replaces the functionality of the Hosts file, which requires manual maintenance at each workstation.

In previous versions of Windows, NetBIOS was used as the primary method of name-to-IP resolution. In Windows 2000, DNS is the default name resolution method. The hierarchical naming structure of DNS compliments the hierarchical planning structure implemented in the Active Directory® directory service, and is used as its naming service. Active Directory is integrated into DNS in other ways as well, for example, system administrators can integrate DNS zones into Active Directory, which provides greater fault tolerance.

Windows 2000 Professional supports DNS dynamic update. Dynamic update is a new standard, specified in RFC 2136, that provides a means of dynamically updating host data in a DNS database. Updates can come from DNS clients and servers, DHCP servers, or Active Directory domain controllers. For more information about dynamic update, see "Configure Dynamic Update" later in this chapter.

Windows Internet Name Service

Windows Internet Name Service (WINS) name resolution provides mapping of static and dynamic NetBIOS names to IP addresses. Computers running Windows 2000 TCP/IP can use WINS if one or more Microsoft™ Windows NT™ Server– based computers configured as WINS servers are available. WINS is a dynamic replacement for the Lmhosts file.

WINS client support is configured with Windows 2000 Professional to maintain compatibility with non-Windows 2000 – based hosts, including clients and servers running previous versions of Windows.

Hosts and Lmhosts Files

Hosts and Lmhosts files, also called host tables , are files that Windows 2000 Professional can use for local name resolution when other methods are not available. An Lmhosts file is a list of NetBIOS name and IP address mappings. When WINS is not available, it is used as a WINS equivalent to resolve remote NetBIOS names to IP addresses. Likewise, a Hosts file is a list of host name to IP address mappings. It is used as a local name resolution resource to resolve host names to IP addresses. You must manually enter the name-to-IP address mappings in Hosts and Lmhosts files.

Broadcast Name Resolution

Computers running Windows 2000 TCP/IP can use local broadcast name resolution, which is a NetBIOS-over-TCP/IP mode of operation defined in RFC 1001/1002 as b-node . It is restricted to the local subnet. This method relies on IP subnet and media access control (MAC)-level broadcasts by a host for name registration and announcement on the network. Each computer in the broadcast area is responsible for challenging attempts to register a duplicate unique name and for responding to name queries for its registered unique name.

Determining Which Name Resolution Method to Use

You need to determine whether Windows 2000 Professional– based clients must be configured to use DNS, WINS, or a combination of the two. In general, DNS is recommended under the following circumstances:

• The client is a member of a Windows 2000 domain that uses Active Directory.
  If the Windows 2000 Professional– based computer is to be made a member of a Windows 2000 domain, DNS must be configured. Active Directory is tightly integrated with DNS, and DNS is used by Active Directory as its locator service. A locator service assists clients in a Windows 2000 domain to find other hosts and services by knowing only the domain name.

• Internet or intranet access using DNS is required.
  You must use DNS if you are using TCP/IP to communicate over the Internet or if your private internetwork uses DNS to resolve host names. If the DNS server is not dynamic update-compliant, DNS can be used in conjunction with WINS to automatically resolve host names.

NetBIOS over TCP/IP (NetBT) support is provided as part of Windows 2000 Professional configuration to provide name resolution and connection services for clients using earlier versions of the Windows operating system, applications and services. If a WINS server is available within your network, configure your Windows 2000 Professional– based computer to use WINS under the following circumstances:

• The client is a member of a non-Windows 2000 domain or workgroup.

• The client is a member of a Windows 2000 workgroup where a DNS server is not available.

• The client is part of a network where the DNS server uses WINS lookup for dynamic name resolution.

• The client uses applications or services that require NetBIOS name resolution.

If a WINS server is not available, configure the Windows 2000 Professional– based client to use a Hosts file for DNS host name resolution, or Lmhosts for NetBIOS name resolution. Otherwise, broadcasts are used to provide NetBIOS name resolution, which cannot resolve host names outside the local subnet.

You also need to determine if automatic configuration is available at the DHCP server. If you use DHCP for automatic configuration, a DHCP server can provide client configuration details (DNS and WINS server addresses, host name). If you do not use DHCP, you must manually configure these parameters.