Lecture 9: The Domain Name System (DNS)

IP Addresses Revisited

In lecture 2 we first introduced the concept of the IP Address of a computer. We stated that it's simply another way of identifying a specific machine -- we could equally use the machine's name to identify it. These two different ways of referring to a system come from two semi-conflicting requirements:

The hierarchical domain-based naming system used in the Internet to identify machines is designed for human usage -- in general, we find this system incredibly convenient to use, having a high correlation with how the Real World^™ is organised.We are very comfortable with the use of names like amazon.com and ironbark.bendigo.latrobe.edu.au.
Actual packet delivery in the Internet is based on a separate, fixed-length (four byte) numeric IP Address. For example, the IP address of ironbark is 149.144.21.60. IP addresses are used by the the routers which implement the Internet's delivery service, the Internet Protocol, or IP, to route packets of data through the Internet to their destination.

The Internet Domain Name System (DNS) is used to provide a mapping between these two alternative identification approaches: the human-oriented domain name and the delivery-oriented IP address. Its most common usage is to look up the IP address corresponding to a known domain name.

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