Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 227
DNS Structure

The Domain Name Space is very much like a file system on Unix or DOS. It starts with a root and branches attach from this root to give an endless array of paths. Each branch in the file system is given a directory name, whereas in DNS it is called a label. Each label can be 63 characters in length, but most are far less than that. This means that each text word between the dots can be 63 characters in length, with the total domain name (all the labels) limited to 255 bytes in overall length assuming a screen line length of 80 characters this is just 3 screen lines.

The IP protocol mandates the use of IP addresses. Any user may use this address to connect to any service on the network; however, for a user to remember the addresses of all the network servers on the network is an impossible task. Users are more likely to remember names than they are to remember numbers.

For those familiar with database environments, the domain name server is simply a database (consisting of information such as names and IP addresses, and much more) to which any station on the network can make queries using the domain name resolver. The domain name system is not necessarily complex, but it is involved. It is based on a hierarchical structure as shown in the slide. The assignment of names is relatively simple and is accomplished via the Internet Registries with the ultimate authority being IANA. The domain name is simply that: a name assigned to a domain For example, isi.edu, cisco.com, and 3Com.com represent the domain name at those companies or educational institutions. The naming within those domains (naming of the hosts) is left up to those individuals who are assigned those domain names. The InterNIC does not care. The hierarchical structure allows hosts to have the same name as long as they are in different branches of the structure or in different domains.

DNS Structure