Tuesday, August 23, 2011

Understanding the Need for Names (domain names)

Humans prefer to use and remember names instead of IP numbers. Names actually solve a number of problems for us in the networked world:
  • They provide a human-friendly reference for a site.
  • They allow the IP number to change, while the name remains constant.
  • They allow multiple IP numbers to be given as possibilities for the same host or service.

You already understand that names provide an easier reference to IP numbers. The second point, however, is that the name can remain fixed but allow the IP number of the host to be changed. IP numbers often change because of network changes, ISP changes, equipment changes, and so on. As long as you remember the name of the Internet site, you are unconcerned about what the actual IP number is that takes you there. The last point is one that is easily overlooked. Looking up ftp.redhat.com (at the time of writing) produced two IP numbers:

It doesn't matter whether these two IP numbers refer to the same ftp host or two different mirror sites for load-balancing purposes. The fact is that, by using either of these IP numbers, you can obtain the same files that you were after. This introduction leads you into the topic of resolving names in this chapter. First, you will learn how to query the local system for information about itself. Then you will learn how to use remote host names, look them up, and turn them into IP numbers.

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