Meaning of dns - domain name system, Computer Network Security

What do you understand by the DNS? Explain the usage of the resource records.

Domain Name System is described below:

The Domain Name Service (DNS) is the hierarchical distributed method/technique of managing the name space of the Internet.  The DNS administratively groups hosts into the hierarchy of authority which allows addressing and other information to be broadly distributed and maintained. A key advantage to the DNS is that it removes the dependence/reliance on’ a centrally maintained file which maps host names addresses. DNS is supported by means of asset of network-resident servers, also known as domain name servers.

The IP address is a numeric address which serves role of the analogous to a telephone number. In representation, addresses always comprises of four numbers; four decimal values separated by periods. Figure drawn below illustrates the addresses. The computer named  for example, is assigned a number of 35.8:1.212. The reason a computer would contain two names is that IP addresses numeric; they can be simply understood and manipulated b the hardware and software that should move information over the Internet. So IP addresses are better-suited t computers, and the domain addresses are better-suited t humans. DNS permits a translation between the domain na and the IP address. Domain names do not necessarily hay the four parts. They may have only two parts-a top-level domain like “edu” or “corn,” preceded by the sub domain or three, four, or various. The limitations of it are written below,

(i) A domain- Mime cannot exceed more than 255 characters and

(ii) Each part of the name cannot exceed more than63 characters.

The DNS translates the simple English address,, for instance, into numbers which Internet computers can understand, such as 123.23.43. 121. In order to perform this efficiently, the Internet has been organized into the number of major domains. Major domains refer to the letters at the end of the simple English address, such as .com. A number of common domains are made in use for the United  States:  .com (commercial); .mil (military),  .edu (education);  .gov government);  .net (Internet service providers and networks-companies and groups related with the organization of the Internet); and .org (organization). Because of the various Internet sites has been developing  exponentially,  the domain  name system is being  expanded  and might also include at least seven additional domains, such as .web for Web. Only the two letters are used outside the United States to recognize the domains; for instance, for United Kingdom .au for Australia; .ca for Canada; .uk; and .for for France.

Domains are managed in a hierarchical manner, so that beneath main domains are various minor domains. As an instance of how the DNS and domains work, looks at the NASA’s SPACE link Internet address which is:

The .top domain is .gov, which represents for government. The domain just below that is

.nasa, which is the NASA domain. Then below which is, .msfc (Marshall Space Flight Center) is one of NASA’s various computer networks. SPACE link recognizes the NASA computer which runs the SPACE link program. SPACE link’s numeric IP address has changed through the years, but its Internet address has stayed same.

Absolute and Relative Domain Names are described below:


Domain names can be either be absolute or relative. An absolute domain name ends with the period  (  whereas  a  relative  one  does  not.  Relative names have to be interpreted in some context to uniquely establish their true meaning. In these cases, a named domain refers to a specific node in the tree and all nodes are under it.


The names of the Domain are case insensitive, so edu and EDU mean the same thing. Component names can be till 63characters and full path names mu should not exceed 255 characters.


In principle, domains can be inserted into tree in two different ways. For instance, could equally well be listed under country domain asç

Resource Records bare described below:

The  ‘name  servers’  which  together  implement  the  DNS  distributed  database,  store resource records (RR)’ for hostname to IP address mapping. Each DNS reply message carries one or more of the resource records.

For the single host, the most ordinary resource record is just its IP address, but various other kinds of resource records also exist. When a resolver provides a domain name to DNS, it gets back the resource records associated with that particular name. Thus the actual function of DNS is to map domain names onto the resource records.

A resource record is the five-tuple. Its format is given to us as follows.

Domain_name Time_to_live Type Class Value

(i) The Domain_name tells us the domain to which this record applies. Normally, various records exist for each of the domain and each copy of the database holds information about the multiple domains. The field is therefore the primary search key used to satisfy queries.

(ii)  The Time_to_live field gives an indication of the stability of the record. Information which is highly stable is assigned a large value. Like 864OO (the number of seconds in I day). Information which is highly volatile is assigned a less value, such as 60 (1 minute).

(iii) The type field tells us about the record type, as listed in the table drawn below.

(iv) The fourth field of every resource record is Class. For the Internet information, it is for all time in. For non Internet information, other codes can make in use.

(v)  Value field, can be or an ASCII string a number, a domain name. The semantics relies on the records type.

Posted Date: 7/20/2012 6:24:16 AM | Location : United States

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