Domain Name Servers (DNS) are an important but invisible from the Internet, and are one of the largest databases on it. Each machine on an Internet is assigned a unique address called an IP address, which is 32 bit number and is expressed as 4 octets. The method user to represent these IP addresses is known as dotted decimal notation “A typical address is:. 199.249.150.4

It is very difficult to take into account the IP addresses of all websites you visit daily, because it is hard to remember sequences of numbers. However, remember the words. This is where domain names come in the box. To connect to a particular site, you need to know your IP address, but it is necessary to know its URL. DNS is the mappings of IP addresses and corresponding names.

Names and numbers

DNS converts machine names (eg www.xyz.com) IP addresses (eg 199.249.150.9). Basically, it translates from a name to an address and an address to a name.

The allocation of IP address for the computer name is called reverse mapping. Http: / / www.xyz.com when you type into the browser, the browser first needs to obtain the IP address of www.xyz.com. The machine uses a directory service to find the IP address and the service is called DNS. When he wrote his first machines www.xyz.com contact a DNS server, asking him to find the IP address for www.xyz.com. This DNS server might then contact other DNS servers on the Internet. DNS is therefore is considered as the global network of servers. The great advantage of DNS is that no organization is responsible for updating. This is what is known as distributed database.

The three-letter codes

A DNS server is a computer that is running the DNS software. The most popular DNS software BIND (Berkeley Internet Name Domain) DNS is hierarchical, the tree-structured system. The top is donated by ‘..’ And is known as the root system. Below the root there are seven immediate sub domain nodes and these are ‘com’, ‘org’, ‘government’, ‘thousand’, ‘red’, ‘education’, ‘int’, etc.

DNS consists of two components

* Server Name
* Resolve

Name Server:

It performs the task of searching for names. Usually there is a name server to a cluster of machines. If the name server does not contain the information requested, it will contact another nameserver. But it is not necessary for all servers to know how to contact each server. Every name server knows how to contact the root nameserver, and this in turn, the location of every authoritative nameserver for all second level domains.

Solve:

It runs on a client computer to initiate DNS lookups. Contains a list of name servers to use. As we read, the function of each of these nameservers is to resolve name queries. There are three types of name server primary nameserver, secondary nameserver, and caching nameserver. The secondary nameservers are configured for backup purposes. Caching nameservers only resolve name queries but do not keep files of DNS database. It is important to note here that any change in the needs of primary name servers to propagate to the secondary name servers. This is because primary nameservers own the database records. The changes are propagated through a “zone transfer.

HOW “CACHING” WORKS

DNS uses principle of “cache” for its operation. When a name server receives information on a map, it caches this information. Other questions in the same mapping will use this cached result, thereby reducing the cost of the search. The name servers do not cache forever. Caching has a component called time to live (TTL) and the TTL determines how long a server cache a piece of information. So when the caches of name servers receive an IP address, which receives the TTL with it. The nameserver caches the IP address for the period of time, that discards.

When a process is to determine an IP address given a DNS address, calls on the local machine to resolve the address. This can be done in a variety of ways:

Table look up. On UNIX hosts, the table is / etc / hosts.

The process communicates with the local name servers. This is called on a UNIX system.

By sending a massage to the remote system is identified from information in the file / etc / resolve.conf.

When a nameserver receives a query for a domain that does not work, can return a reference to the client by specifying server names. They usually operate in a recursive manner wherein any DNS server passes requests it can not handle the higher level server and so on, until the request can be handled or until the root DNS name space is reached.

Name servers contain links to other name servers with the help of which you can go all the domain name hierarchy. A host with the addresses of the initial name server must be configured. After this, it is able to use DNS protocols to locate the nameserver responsible for any part or the DNS naming hierarchy.

Thus when a nameserver receives a request, you can do one of the following:

You can answer the request with an IP address. This method is called iterative. In this, the client simply asks the server to resolve a domain name. The server accesses its database, finds its IP address and sends back. If the server does not find the address, it sends back an error, DNS not found ‘). Contact another nameserver and try to find the IP address for the requested name. Return a reference to the client specifying the IP address of the server names.

nslookup’is available on the UNIX A popular user interface, called ‘. With this, you can perform any DNS function. This program also shows the result for the user. Using is nslookup, you can get a list of all hosts in a zone. To do this, you must first identify the name server for the zone.

The threats associated with the DNS are due to the lack of integrity and authenticity checking of the data contained in the DNS. In addition, other protocols can use host names as an access control mechanism. The Working Group Internet Engineering Task Force (IETF) has come up with DNS security (DNSSEC) extensions to DNS protocol. The main goal of DNSSEC is to provide authentication and integrity to the DNS. These are provided through the use of cryptography “