There are two copies of zone files available, they are
1. Master file
2. Slave file.

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

Domain Name	Meaning
com	Commerical Organistion
edu	Education Institutions
gov	Government (US)
mil	Military groups

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.

Zone is a group of contiguous domains and subdomains. If the zone has a single domain, then zone and domain are the same.

(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) URL is made up four parts-protocols, hostname, folder name and file name. .
(ii) Each part has its own specific functions. Depending on the applications, additional information can be added to the URL but the common and fundamental URL consists of these four parts.
a. Protocol
b. Domain name/Hostname
c. Folders
d. The file name with extension

(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(.)

No.	IPv4	IPv6
1.	IPv4 address is a 32 bit unique address given to a computer system.	IPv6 address is a 128 bit unique address given to a computer system.
2.	There are two ways to represent the IP address: Binary notation, Dotted-decimal notation.	It follows Hexadecimal number notation.
3.	The number of address that can be formed is 232.	The number of addresses formed in IPv6 is 2128

(i) Domain Name System (DNS) maintains all the directory of domain names and help us to access the websites using the domain names.
(ii) It translates the domain name into IP address.
(iii) The foure important components of the Domain Name System are Namespace, Name Server, Zone and Resolver.

(i) To avoid the major disadvantage of Flat namespace, hierarchical namespace is used in large
(ii)  Hierarchical namespace is where the name is made up of several parts.
a. First part may represent the nature of the organization.
b. Second part may represent the name of the organization, and
c. Third part may represent the department of the organization and so on.
(iii) In this way the power to control the namespace can be decentralized.
(iv) The centralized authority can be given to nature and then to the name of the organization and so on.
(v) To achieve hierarchical namespace, Domain Name Space was designed.

(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).

Name Server:
(i) Name Server is a main part of the Domain Name System (DNS). It is a software program that run on a physical system.
(ii) It has the DNS database consisting of domain names and their corresponding IP addresses. Name Server translates the domian name to IP address.
(iii) There is a need to store a large number of domain names for worldwide usage, so plenty of servers are used in the hierarchical manner.
(iv) Name servers do the important task of searching the domain names. While you searching for a website, Local Nameserver (provided by ISP) asks the different name servers until one of them finds out the answer.
(v) At last it returns IP address for that domain name. Your computer is now connected to the requested webpage.
Types of Name Servers:
There are three types of Name servers which control the entire Domian Name System:
(i) Root Name Server - top level server which contains entire DNS tree, maintained by ICANN. There are 13 servers.
(ii) Primary Name Server - contains a zone resource records. These records are updatable by domain name holders.
(iii) Secondary Name server - contains a copy of primary server files. This server has no authority to update, but reduce the workload of primary server by sharing the queries.