DNS is a distributed data system that works at the transport layer to provide name-to-address mapping for client applications. DNS servers maintain databases that consist of hierarchical name structures of the various domains in order to use logical names for device identification. This type of address/ name resolution is called service-provider initiated. The largest use of DNS is in the internet.
Sun Micro-systems developed the Domain Name System (DNS) in the early 1980s as an easier way to keep track of internet addresses. The Internet Protocol (IP) uses Internet address information to deliver mail and other data from computer to computer. Every IP address on the internet is actually a series of four numbers seperated by periods called dots, such as 163.52.128.72. But it will be difficult to remember numeric addresses to communicate with someone using electronic mail. The DNS establishes a hierarchy of domains, which are groups of computers on the internet.
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The DNS gives each computer on the net an internet address, or domain name, using easily recognizable letters and words instead of numbers.
Domain Name System (DNS) is the standard for resolving names to Internet addresses. However, the hosts file still plays a role in name resolution during the booting of a system and as a means to provide LAN resolution when DNS is down. In a nutshell, DNS is a distributed database whose structure looks like the UNIX file system. DNS is a client / server system in which the resolvers query the named servers to find an address record for a domain name. The query process begins with the root name servers. If the root name server does not know the answer, it returns the address of a name server that knows more details about the domain name. The resolver then queries the new name server. This iterative process continues until a name server responds with the address of a domain name.
The root of DNS database on the internet is managed by the Interenet Network Information Center (http://www.internic.com). The top-level domains were assigned organization wise, and by country.
DNS is a protocol that can be used in different platforms. In the Internet, the domain name space (tree) is divided into the three different sections :::
(a) Generic domains
(b) Countary domains
(c) Inverse domains
The generic domains define registered hosts according to their generic behaviour. Each node in the tree defines a domain, which is an index to the domain name space database. The first level in the generic domain-section allows seven possible three character lebels. These labels describe the organization types as listed ---
..............................................................................................
Label Description
..............................................................................................
com Comercial organization
edu Educational institutions
gov Government institutions
int International organization
mil Military groups
net Network support centers
org Nonprofit organization
.................................................................................................
Recently a few more first-level labels have been proposed. These are listed in Table 2.
........................................................................................................
Label Description
.......................................................................................................
art Cultural organizations
firm Bussiness or firms
info Information service provider
nom Personal nomenclatures
rec Recreations/entertainment organization
store Business offering goods to purchase
web Web-related organizations
.............................................................................................................
The Country domain section follows the same format as the generic domains but uses two-character country abbreviations (e.g; "us" for United States) in place of the three-character organizational abbreviations at the first level. Second-level labels can be more specifies, national destinations. The United States, for example, uses state abbreviations as a subdivision of "us" (e.g., ca.us.).
The inverse domain is used to map an address to a name. This may happen, for example, when a server has received a request from a client to do a task. Whereas the server has a file that contains a list of authorized clients, the server lists only the IP address of the client (extracted from the received IP packet). To determine if the client is on the authorized list, it can send a query to the DNS server and ask for mapping of address to name.
A DNS server is any computer registered to join the Domain Name System. It runs special-purpose networking software, features a public IP address, and contains a database of a network names and addresses for other Internet hosts.
DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top of this hierarchy are root servers that store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers named A, B, C and so on up to M. The other DNS servers are installed at lower levels of the hierarchy and maintain only certain pieces of the overall database.
Most of the lower-level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example, Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other domains. Similarly, ISP's maintain DNS servers for their customer's Internet connection setup.
When we type a url in our web browser, the web browser acts as a DNS client and sends a request to our ISP's DNS servers. The DNS server will then search its database for a matching name is not in its database, it automatically passes that request to another DNS server or to the next higher level server in the DNS hierarchy. Eventually the request will arrive at a server that has the matching name and IP address in its database. This server will then issue the response which will flow back through the chain of DNS servers to the client.
Sun Micro-systems developed the Domain Name System (DNS) in the early 1980s as an easier way to keep track of internet addresses. The Internet Protocol (IP) uses Internet address information to deliver mail and other data from computer to computer. Every IP address on the internet is actually a series of four numbers seperated by periods called dots, such as 163.52.128.72. But it will be difficult to remember numeric addresses to communicate with someone using electronic mail. The DNS establishes a hierarchy of domains, which are groups of computers on the internet.
.gif)
The DNS gives each computer on the net an internet address, or domain name, using easily recognizable letters and words instead of numbers.
Domain Name System (DNS) is the standard for resolving names to Internet addresses. However, the hosts file still plays a role in name resolution during the booting of a system and as a means to provide LAN resolution when DNS is down. In a nutshell, DNS is a distributed database whose structure looks like the UNIX file system. DNS is a client / server system in which the resolvers query the named servers to find an address record for a domain name. The query process begins with the root name servers. If the root name server does not know the answer, it returns the address of a name server that knows more details about the domain name. The resolver then queries the new name server. This iterative process continues until a name server responds with the address of a domain name.
The root of DNS database on the internet is managed by the Interenet Network Information Center (http://www.internic.com). The top-level domains were assigned organization wise, and by country.
DNS is a protocol that can be used in different platforms. In the Internet, the domain name space (tree) is divided into the three different sections :::
(a) Generic domains
(b) Countary domains
(c) Inverse domains
A. GENERIC DOMAINS ::
The generic domains define registered hosts according to their generic behaviour. Each node in the tree defines a domain, which is an index to the domain name space database. The first level in the generic domain-section allows seven possible three character lebels. These labels describe the organization types as listed ---
..............................................................................................
Label Description
..............................................................................................
com Comercial organization
edu Educational institutions
gov Government institutions
int International organization
mil Military groups
net Network support centers
org Nonprofit organization
.................................................................................................
Recently a few more first-level labels have been proposed. These are listed in Table 2.
........................................................................................................
Label Description
.......................................................................................................
art Cultural organizations
firm Bussiness or firms
info Information service provider
nom Personal nomenclatures
rec Recreations/entertainment organization
store Business offering goods to purchase
web Web-related organizations
.............................................................................................................
B: COUNTRY DOMAINS ::
The Country domain section follows the same format as the generic domains but uses two-character country abbreviations (e.g; "us" for United States) in place of the three-character organizational abbreviations at the first level. Second-level labels can be more specifies, national destinations. The United States, for example, uses state abbreviations as a subdivision of "us" (e.g., ca.us.).
C. INVERSE DOMAINS ::
The inverse domain is used to map an address to a name. This may happen, for example, when a server has received a request from a client to do a task. Whereas the server has a file that contains a list of authorized clients, the server lists only the IP address of the client (extracted from the received IP packet). To determine if the client is on the authorized list, it can send a query to the DNS server and ask for mapping of address to name.
DNS SERVER
A DNS server is any computer registered to join the Domain Name System. It runs special-purpose networking software, features a public IP address, and contains a database of a network names and addresses for other Internet hosts.
DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top of this hierarchy are root servers that store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers named A, B, C and so on up to M. The other DNS servers are installed at lower levels of the hierarchy and maintain only certain pieces of the overall database.
Most of the lower-level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example, Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other domains. Similarly, ISP's maintain DNS servers for their customer's Internet connection setup.
When we type a url in our web browser, the web browser acts as a DNS client and sends a request to our ISP's DNS servers. The DNS server will then search its database for a matching name is not in its database, it automatically passes that request to another DNS server or to the next higher level server in the DNS hierarchy. Eventually the request will arrive at a server that has the matching name and IP address in its database. This server will then issue the response which will flow back through the chain of DNS servers to the client.
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