Windows 2000 DNS

Naming Hosts and Domains

In Windows NT 4.0 and earlier, a computer is identified primarily by a NetBIOS name — it is by this name that the computer is known on the network. In Windows 2000, a computer is identified primarily by its full computer name, which is a DNS fully qualified domain name (FQDN). The same computer could be identified by more than one FQDN. However, only the FQDN that is a concatenation of the host name and the primary DNS suffix is the full computer name. In this chapter, the first label of the full computer name is known as the host name, and the remaining labels form a primary DNS suffix.

By default, the primary DNS suffix of a computer that is running Windows 2000 is set to the DNS name of the Active Directory domain to which the computer is joined. The primary DNS suffix can also be specified by Group Policy, discussed later in this section.

Note

You can set and view the FQDN from the Network Identification tab of the System Properties dialog box, which you can go to by right-clicking My Computer, and then clicking Properties. To change the host name, click Properties and then to change the primary DNS suffix, click More.

Suppose that you have a WINS client named Client1. The name "Client1" will be the computer's NetBIOS name. Next, suppose that you replace WINS with DNS on your network and make Client1 a DNS client in the domain eu.reskit.com. The name Client1 is now also the computer's host name, and it is by default concatenated with the primary DNS suffix eu.reskit.com to make the FQDN Client1.eu.reskit.com.

The NetBIOS name is derived from the host name, but the two names might not be identical. The NetBIOS name is a 16-byte string that uniquely identifies a computer or service for network communication. It is used by all the Windows 2000 network services to uniquely identify themselves. If the DNS host name is 15 or fewer bytes, the NetBIOS name is the host name plus enough spaces to form a 15-byte name, followed by a unique identifier, the sixteenth byte, that specifies the network service. If the DNS host name is longer than 15 bytes, then by default, the NetBIOS name is the host name, truncated to 15 bytes, plus the service identifier. If you try to create two DNS host names and the first 15 bytes are the same, you are prompted to enter a new name for NetBIOS.

Note

Because host names are encoded in UTF-8 format, they do not necessarily have only 1 byte per character. ASCII characters are 1 byte each, but the size of extended characters is more than 1 byte.

Windows 2000 also allows each adapter to have its own DNS suffix, which is known as a connection-specific DNS suffix. The connection-specific DNS suffix is usually assigned by a DHCP server that leases an IP address to the adapter. On computers that are running Windows 2000, in addition, an administrator can assign a connection-specific DNS suffix to statically configured adapters.

Depending on the configuration, the connection-specific DNS suffix can be appended to the host name to create an FQDN that is registered in DNS. For example, suppose that the computer Client1 has the primary DNS suffix reskit.com, and Client1 is connected to both the Internet and the corporate intranet. For each connection, you can specify a connection-specific DNS suffix. For the connection to the corporate intranet, you specify the name reskit.com, and the FQDN is then Client1.reskit.com. For the connection to the Internet, you specify the name isp01-ext.com, and the FQDN is then Client1.isp01-ext.com. Figure 6.1 shows this configuration.

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Figure 6.1 Connection-Specific Domain Names

You can specify connection-specific DNS suffixes for statically configured adapters and adapters configured by DHCP on the DNS tab in the Advanced TCP/IP Settings dialog box. In that dialog box, you can also specify whether the client uses its connection-specific DNS suffix in addition to its primary DNS suffix when it registers its FQDN. For more information about configuring DHCP clients for DNS, see "Dynamic Update" later in this chapter.

Caution

If you have any multihomed dynamic update clients and at least one adapter is using DHCP, configure the DHCP server to update resource records according to the request of the client. For more information about how to configure DHCP servers to update resource records, see "Dynamic Update" later in this chapter. If the DHCP server is configured to register both A and PTR resource records, the DHCP server replaces all A resource records for the name it attempts to register. As a result, A resource records that correspond to the IP addresses for the computer's other addresses might be deleted.

Table 6.1 summarizes the differences between each kind of name using the example FQDN client1.reskit.com.

Table 6.1 DNS and NetBIOS Names

Name Type	Description
NetBIOS name	The NetBIOS name is used to uniquely identify the NetBIOS services listening on the first IP address that is bound to an adapter. This unique NetBIOS name is resolved to the IP address of the server through broadcast, WINS, or the LMHosts file. By default, it is the same as the host name up to 15 bytes, plus any spaces necessary to make the name 15 bytes long, plus the service identifier. The NetBIOS name is also known as a NetBIOS computer name. For example, a NetBIOS name might be Client1.
Host name	The term host name can mean either the FQDN or the first label of an FQDN. In this chapter, host name refers to the first label of an FQDN. For example, the first label of the FQDN client1.reskit.com is client1.
Primary DNS suffix	Every Windows 2000–based computer can be assigned a primary DNS suffix to be used in name resolution and name registration. The primary DNS suffix is specified on the Network Identification tab of the properties page for My Computer. The primary DNS suffix is also known as the primary domain name and the domain name. For example, the FQDN client1.reskit.com has the primary DNS suffix reskit.com.
Connection-specific DNS suffix	The connection-specific DNS suffix is a DNS suffix that is assigned to an adapter. The connection-specific DNS suffix is also known as an adapter-specific DNS suffix. For example, a connection-specific DNS suffix might be acquired01-ext.com.
Full computer name	The full computer name is a type of FQDN. The same computer could be identified by more than one FQDN. However, only the FQDN that is a concatenation of the host name and the primary DNS suffix is the full computer name.
Fully qualified domain name	The FQDN is a DNS name that uniquely identifies the computer on the network. By default, it is a concatenation of the host name, the primary DNS suffix, and a period. For example, an FQDN might be client1.reskit.com.