Information Technology Reference
In-Depth Information
Following these steps should drive home the concept of DNS for you because you can see
it working to make your life easier. Now you don't have to remember 10.0.0.10; you only
need to remember exchange03. However, you can also see how this method can become
unwieldy if you have many hosts that want to use easy-to-remember names instead of IP
addresses to locate resources on your network.
When dealing with large networks, users and network administrators must be able to
locate the resources they require with minimal searching. Users don't care about the actual
physical or logical network address of the machine; they just want to be able to connect to
it using a simple name that they can remember.
From a network administrator's standpoint, however, each machine must have its own
logical address that makes it part of the network on which it resides. Therefore, some
scalable and easy-to-manage method for resolving a machine's logical name to an IP
address and then to a domain name is required. DNS was created just for this purpose.
DNS is a hierarchically distributed database. In other words, its layers are arranged in
a definite order, and its data is distributed across a wide range of machines, each of which
can exert control over a portion of the database. DNS is a standard set of protocols that
defines the following:
■
A mechanism for querying and updating address information in the database
■
A mechanism for replicating the information in the database among servers
■
A schema of the database
DNS is defined by a number of requests for comments (RFCs), though pri-
marily by RFC 1034 and RFC 1035.
DNS was originally developed in the early days of the Internet (called ARPAnet at the
time) when it was a small network created by the Department of Defense for research
purposes. Before DNS, computer names, or hostnames, were manually entered into a
HOSTS file located on a centrally administered server. Each site that needed to resolve
hostnames outside of its organization had to download this file. As the number of
computers on the Internet grew, so did the size of this HOSTS file—and along with it the
problems of its management. The need for a new system that would offer features such as
scalability, decentralized administration, and support for various data types became more
and more obvious. DNS, introduced in 1984, became this new system.
With DNS, the hostnames reside in a database that can be distributed among multiple
servers, decreasing the load on any one server and providing the ability to administer this
naming system on a per-partition basis. DNS supports hierarchical names and allows for
the registration of various data types in addition to the hostname-to-IP-address mapping
used in HOSTS files. Database performance is ensured through its distributed nature as
well as through caching.
The DNS distributed database establishes an inverted logical tree structure called the
domain namespace
. Each node, or domain, in that space has a unique name. At the top
of the tree is the root. This may not sound quite right, which is why the DNS hierarchical
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