Sams Teach Yourself MCSE Windows NT Server 4 in 14 Days
(Publisher: Macmillan Computer Publishing)
Author(s): David Schaer, et al
ISBN: 0672311283
Publication Date: 12/15/97

11.4.5. LMHOSTS Files

Before WINS, NetBIOS name resolution relied on a file called the LMHOSTS file. This file is very simple and looks something like the following:

Each entry in this file lists an IP address and its corresponding NetBIOS name. Each entry can also include one or more keywords. The keywords that may be used are summarized in Table 11.2.

The LMHOSTS file requires that all mappings be entered manually. Obviously, the capability of WINS to dynamically associate mappings is a great improvement over the LMHOSTS file, but LMHOSTS can still be useful on clients that do not support WINS.

11.4.6. HOSTS Files

AOne flaw in the WINS and LMHOSTS scheme is that non-WINS enabled clients cannot use WINS to resolve NetBIOS name to IP address. The HOSTS file is used for just that purpose. It is structured similarly to the LMHOSTS file:

In each entry is the IP address and corresponding host name of a computer. Note the difference between this and the LMHOSTS file, however. In the LMHOSTS file, one IP address can be associated with exactly one NetBIOS name. In the HOSTS file, however, the same IP address can be associated with multiple host names. Thus, you can get to 192.168.0.1 by using either server1 or server1.domain1.com.

The first entry of localhost refers to the local client by the loopback address 127.0.0.1, which is typically used for diagnostics.

11.5. Domain Name System (DNS)

During the Internet’s early years, when it was known as ARPANET, it consisted of only a few hundred computers networked together. With these few computers, keeping track of the host names and IP addresses of these computers was a fairly simple task. These mappings were located in a central file called Hosts.txt, which was located on a host computer at the Stanford Research Institute. As the ARPANET grew, however, this file became more difficult to manage for a few reasons:

•  The file was growing too large to manage efficiently.

•  All of the traffic on ARPANET had to be routed through the Stanford computer to resolve computer host names.

•  The file had a flat name structure, meaning that every computer connected to ARPANET had to have its own unique host name.

The domain name system (DNS) is a distributed database that uses a hierarchical name structure. The function of this database is to resolve host names or fully qualified domain names (FQDN) to IP addresses. The database is distributed across many computers on the Internet, which means that name resolution no longer requires going through a central point, as it did with the Hosts.txt file. Its name space is also hierarchical, which means that it is like a tree structure (see Figure 11.25).

Figure 11.25.  The domain name space.

Each node in this structure is called a domain. The domain name space is typically divided into three domain levels: root level, top level, and second level. Domains represent different levels of authority in this hierarchical structure. The highest level of authority is called the root domain. The top-level domains are organizationally defined, as shown in Table 11.3.