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Domain Name Servers (DNS) are an important but invisible part of the internet, and form one of the largest databases on it. Each machine has a unique Internet address, called an IP address, which is 32 and the number of bits is expressed as four bytes. . The method user to represent these IP addresses is known as dotted decimal notation "A typical address looks like this: 199.249.150.4
It is very difficult to take into account the IP addresses of all the places we visited every day, because it is not easy to remember strings of numbers. However, remember the words. This is where domain names come into play. To connect to a particular site, it is necessary to know the IP address, but it is not necessary to know its URL. The DNS gets the mappings of IP addresses and the corresponding names dns.
Names and numbers
DNS converts machine names (like http://www.xyz.com) into IP addresses (like 199.249.150.9). Basically, it translates from a name to an address and an address to a name dns.
Mapping the IP address of the machine name is called reverse mapping. When writing http://www.xyz.com in your browser, the browser must first obtain the IP address http://www.xyz.com. The machine uses a directory service to look up IP addresses and this service is called DNS. When he wrote his first machines http://www.xyz.com contact a DNS server, asking it to find the IP address http://www.xyz.com. This DNS server might then contact other DNS servers on the Internet. Therefore, considering the overall DNS server network. The great advantage of DNS is that no organization is responsible for the update. This is what is known as a distributed database.
DNS:
A DNS server is a computer running the DNS software. The most popular DNS software is BIND (Berkeley Internet Name Domain) DNS is hierarchical, tree system. The signal is given by '.'. And it is known as the root system. Below the root there are seven immediate sub domain nodes and these are "com", "org", "gov", "mil", "red", "edu", "Int", etc
DNS comprises two components
Name server
resolver
Server Name:
It performs the task of looking at the names. Usually dns there is a name server for a group of machines. If the name server does not contain the requested information, it will contact another nameserver. But it is not necessary that each dns server to know how to communicate with all other servers. Each server will know how to contact dns the root name server, and in turn the location of every authoritative name server for all second level domains.
solve:
This is running on a client computer to initiate DNS lookups. Contains a list of nameservers to use. As we read, the function of each of these servers is to resolve dns name queries. There are three types of name servers primary name server, secondary name server and name server cache. Secondary servers are configured for backup. Caching servers only resolve name queries but do not store files DNS database. It is important to note that any change in the primary nameservers needs to be propagated to the secondary servers. This is because the primary name servers own database records. The changes are propagated via a 'zone transfer.
How to "caching works
DNS uses the principle of caching for the function. When a name server receives information on an application is cached requests this information for the same mapping will use this cached result, thereby reducing the cost of research. Servers dns can not always hide. The caching has a component called time to live (TTL) and the value determines how long the server a piece of information is hidden. So when the name cache servers receive an IP address, it receives dns the TTL with it. The name server caches the IP address for the period of time and then discarded.
When a dns process is to determine a given IP address a DNS address, he asked the local host to resolve the address. This can be accomplished in a variety of ways:
Search. On UNIX hosts, the dns table is / etc / hosts.
The process communicates with the local name servers. This dns is the name of a UNIX system.
By sending a massage on the remote system that is identified from information in the / etc / resolve.conf file.
When a name server receives a query for a domain that is not in use, you can return a reference to the client by specifying better nameservers. Usually operate in the recursive manner in which any DNS server passes requests it can not handle more server level and so on, until the request can be processed or to the root of the DNS namespace is reached.
The nameservers contain pointers to other name servers with which you can navigate through the hierarchy of domain names. With a host address of the original server name you want to configure. After that, he is able to use DNS protocols to locate the server responsible for all or part of the hierarchy of DNS names names.
So when a name server receives a request, you can do dns one of the following:
You can respond to the request with an IP address. This iterative method is called. In this, the client simply asks the server to resolve a domain name. The server accesses its database, finds its IP address and sends it back. If the server can not find the address, it returns an error; DNS not found "). Contact another nameserver and try to find the IP address for the requested name. Returns dns a reference to the client specifying the IP address of the servers best names.
A popular user interface, called "nslookup'is available on the UNIX system. With this, you can perform a DNS function. Program also displays the result to the user. Usage is nslookup, you can get a list of all hosts in a zone. to do this dns, you first need to identify the name server for the zone.
Threats associated with the DNS are due to the lack of integrity and authenticity of data verification in the DNS. In addition, other protocols can use host names as access control mechanism. The Working Group of the Internet Engineering Task Force (IETF) has developed the DNS Security Extensions (DNSSEC) in the DNS protocol. The main objective is to provide DNSSEC authentication and integrity of DNS. These are provided by the use of cryptography '
