Domain Name System
Domain Name System (DNS) is a simple and scalable directory system for the Internet. Its most important function is to translate a machine name that is in the form www.xyz.com into an IP address. It is not possible for humans to remember hundreds of addresses, particularly when there are no semantics associated with the address. Also, IP addresses are allocated dynamically and hence remembering IP addresses may be meaningless. On the other hand, the network layer can handle only addresses. This necessitates a scalable system that can translate a name to an IP address.
DNS achieves this by defining a domain name hierarchy. There is the concept of a root. The root server address is well known. In fact, there are few well-known root servers. Under the root there are a few well-defined domains as shown in Figure 2.9.
Figure 2.9. DNS hierarchy.
Under each of these well-known domains exists one or more organizations belonging to that domain. In our example, com domain is registered under the root server and the company xyz is registered under com domain. Registering implies that the organization is running a domain name server that can answer to queries.
When a client wishes to talk to a host, it requests the resolver (software that resolves the domain name to an IP address) to resolve the domain name to an IP address. For example, when you enter www.xyz.com in your browser, the browser requests the resolver to map www.xyz.com to an IP address. The resolver goes through a well-defined process to resolve the domain name to an IP address. This algorithm is beyond the scope of this book. After the domain name is resolved, the client is ready to communicate with the www.xyz.com Web server.
In addition to resolving DNS names, DNS is also used to resolve the mail host, that is, where to send all the mail destined to the company xyz.com. DNS is also being enhanced to perform other directory services. The reader is urged to refer to it for a better understanding of DNS and its capabilities.
Top IPSec (2nd Edition) ISBN: 013046189X
EAN: 2147483647 Year: 2004
Pages: 76 Authors: Naganand Doraswamy, Dan Harkins
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