India, Singapore, Srilanka

Each node in the DNS tree-like structure has a name, called a label. Label is a string having a maximum of 63 characters.

1. Root element is present at the top most level (ie) level 0.
2. Next level to the root element is node (children of root element)
3. Each node in the tree has a label and a domain name.

Domain is a sub tree in domain name space tree structure.

URL (Uniform Resource Locator) is the address of a document on the Internet. URL is made up of four parts: protocols, hostname, folder name and file name. Each part has its own specified functions.

(i) Domain Name System is a client server application.
(ii) A host system need to map domain name to IP address or vice versa according to the call and that work is done by resolver .
(iii) Resolver either asks server to provide information about IP address.
(iv)  If it doesn't find any information, then it sends the request to other servers and so on.
(v)  Once the resolver receives the mapping, it checks whether it is an error or resolution (mapping) and provides result according to that

(i) Country domain uses 2-character Country abbreviation according to country.
(ii)  For e.g., google.in - for INDIA, Google's for US. Some of the Domain Name and their meaning

(i)  Flat name space is where the name is assigned to the IP address.
(ii)  They do not have any specific structure .
(iii) In this flat namespace, some meaningful names are been given to IP address for accessing.
Disadvantage:
(i)  Flat name Space cannot be used in large system. Because they need to be accessed and controlled centrally to avoid ambiguity and redundancy.
(ii)  But it is difficult in flat name system. To avoid this major disadvantage hierarchical name space is used in large.

(i) Domain name is the sequence of labels. In domain name the sequence of labels are separated by dot(.).
(ii) The domain name is always read from the lower level to higher level i.e., from the leaf node to root node.
(iii) The domain name which is obtained by reading the labels from bottom to top, separating each label by dot(.)

(i) Domain can consist of Alphabets a through z, and the digits 0 through 9.
(ii) Hyphens are allowed, but hyphens can not be used as first character of a domain name.
(iii) Spaces are not allowed
(iv) Special symbols (such as !, $, &, _ and so on) are not permitted .
(v) Domain names have the minimum length of 2, and the maximum length of 63 characters. The entire name may be at most 253 characters long.
(vi) Domain names are not case-sensitive. (It may be upper, lower or mixing of both case letters).

Domain Name Space :

(i) Domain name space was designed to achieve hierarchical name space. In this, the names are represented as a tree like structure with a root element on the top and this tree can have a maximum of 128 levels starting from root element, taking level 0 to level 127
(ii) The above figure represents the domain name space where the root element is present at the top most level i.e., level 0.
(iii) The root element always represents the NULL string. The next level to the root element is node. Each node in the tree has a label and a domain name.
Label:
(i) Label is a string having a maximum of 63 characters. Each node in that level should have different labels, thereby assuring the individuality of the domain name.
(ii) In other words, Labels are the names given to domains. Domain is a sub tree in domain name space tree structure. The domain can be further divided into sub domains.
(iii) The domain name which is obtained by reading the labels from bottom to top, separating each label by dot (.).

Domain name :
(i) It is the sequence of labels. In domain name the sequence of labels are separated by dot (.).
(ii) The domain name is always read from the lower level to higher level i.e., from the leaf node to root node. Since the root node always represent NULL string, all the domain name ending with dot.