Domain Name System (DNS)
 How to Secure  Windows Usage?
 Domain Name System  (DNS)
 Abstracts from the  Informatics World
 CISN Archive
 Send Feedback

The Internet world runs on the IP system. Two different numbering systems, Ipv4 and Ipv6, have been devised. Ipv6 has been introduced due to the shortcoming (specifically the digital one) of the Ipv4 system.

It is only natural that in the Internet world, what we see are names rather than IP address numbers. It is easier to recall names than IP addresses which would be difficult to remember. The name system corresponding to IP addresses is termed as the "Domain Name System" (DNS). The domain names simplify our work at many places.

Even though there are numerous software programs for the purpose, the most widely preferred one is BIND ( which is an open source coded facility. In short the Domain Name System functions as follows:
                    ^^ Root domain name.
             ^^^ Secondary domain name.
     ^^^^ Other domain names.

The info about which domain name is to be kept by whom, resides on the Root source servers. For instance, it is known that .tr domain names are kept on the servers (At the time of this script they are kept on six servers). After the root servers, (continuing with the .tr example) main servers are there to keep the other sub domain names. In Türkiye there exists secondary domain names such as,,, Some other countries (Germany, .de, for example), however, have not chosen this structure. To this date, there are twenty sub domain name groups under .tr such as, You may make use of the address for further information about .tr domain name management.

When we consider address as an example:

From right to left; root servers will indicate who .tr belongs to. Having obtained the info, the DNS would inquire to the .tr servers about who is responsible for By coincidence the same servers i.e. .tr servers, are also responsible for The next inquiry to the servers will be about who is in charge of address. Receiving the answer, the final question 'what is the IP of address' will be directed to DNS servers. The DNS servers of METU are named as and

The point to ponder in this process is that the inquiry system should have a defined directory tree. In other words, the root directory will not respond to the IP address of address inquiry. It is necessary to get the answer from the related domain name server.

As users what is crucial for us is that there should be a defined IP address for each domain name. Domain name servers, at some instances, may be maladjusted or may not function. At such mayhap it may be necessary to investigate the domain name server. For this purpose the commands, nslookupfor Microsoft operating systems and host for UNIX/LINUX operating systems are incorporated. Of course, besides these software like dnstop, dnstracer are also available.

It is not necessary for the names of the computers on the operating systems to be the same as the names existing in the DNS. The differences in the names will not hinder the operation of the system and, in some cases, might even prove to be helpful.

For name systems there two important outstanding criteria defined and named as forward (from name to IP) and reverse (from IP to name) in name systems. Not having these defined or wrongly defined does sometimes obscure the functioning of the system. For instance, systems with wrong settings of forward and reverse face problems when sending e-mail.

Furthermore, IPs without name definitions or false name definitions are considered to be used for wrong deeds. That is why such systems are not welcomed on the net and service is not provided.

DNS servers are capable of finding records not in itself from a higher server it is connected to and conveying these to the users. In this structure that is called recursive questioning, any domain name around world is searched at the related DNS server and then passed on to the user. The information is kept at the cache of the server for a certain time and thus it is made possible for the server to answer similar inquiries from itself much more rapidly. The DNS servers of METU welcomes any questioning from within the campus. The recursive enquiries are closed to off campus connections and will only respond to enquires related to METU.

For the internet system to function properly and to receive appropriate service the name definitions must be accurate. System and network administrators must be responsive regarding the issue.

Hüsnü Demir - Ozan Saygın Caner

  - TOP -