The simplest method of hostname resolution uses the HOSTS file. This is a lookup table formatted as an ASCII text file and stored in systemrootdriversetcHOSTS. This file follows the format of the HOSTS file in BSD Unix 4.3.

The HOSTS file lists IP addresses, each followed by one or more hostnames to act as aliases for that address, separated by spaces or tabs. The # symbol begins a comment. The following is a simple example of a HOSTS file:

# HOSTS file
# (This is a comment)
127.0.0.1       localhost     # Loopback to local host
192.168.0.1     thismachine   # Alias to my actual address
209.68.11.152   starling      # A frequently used host

Entries in the HOSTS file are resolved very quickly and do not require connection to a name server, so this file is convenient to use for hosts that you will frequently access via FTP, Telnet, or other utilities.

DNS is a standard for hostname resolution that was first developed for Unix; it is defined by RFCs 1034 and 1035. DNS is the standard for name resolution on the Internet and is also used locally in many networks. Windows NT machines can act as DNS clients or servers.

A DNS client sends a hostname to the server and receives an IP address in response. Hostnames can range from simple machine names on a local network to subdivided names, such as www.figby.com, used on the Internet. Internet hostnames use a hostname, a domain name, and a top-level domain name (TLD). The most common TLDs are listed in Table 18-10. An entire hostname with its TLD is referred to as an FQDN, or fully qualified domain name .

As with IP addresses, the InterNIC formerly assigned domain names under the COM, NET, and ORG TLDs. This task has now been turned over to an ever-expanding group of competing registrars, managed by the Internet Corporation for Assigned Names and Numbers (ICANN).

Configuring DNS

After the DNS server is installed, you can manage the service from the DNS Manager MMC snap-in. To access this utility, select Programs → Administrative Tools → DNS from the Start menu. The DNS Manager snap-in is shown in Figure 18-4.

Figure 18-4. The DNS Manager MMC snap-in

You can add either forward- or reverse-lookup zones from this window or modify existing zones. To add a zone, right-click in the empty window or select New Zone from the Action menu. This displays the New Zone Wizard, which prompts you for the following information:

1. A welcome dialog is displayed. Click Next to continue.

2. Choose a zone type: Active Directory-integrated, which stores the DNS information in the Directory; Standard Primary, which creates an NT 4-style primary zone; or Standard Secondary, which creates a secondary copy of a primary zone.

3. Click Next to continue.

4. Choose whether the zone will be forward-lookup (returns IP addresses for names) or reverse-lookup (returns names for IP addresses) and click Next.

5. Choose a name for the zone. This typically includes the domain name, such as zone2.figby.com. Click Next to continue.

6. For a non-Active Directory zone, choose whether to create a new zone file or to load the contents of an existing file (typically from a backup or another computer). Click Next to continue.

7. A final summary dialog is displayed. If the information shown is correct, click Finish to create the zone and exit the wizard.

On the Exam

You can also modify zones by editing the zone files stored in the systemrootsystem32DNS directory. These are standard ASCII files.