If you spend any time on the internet sending e-mail or browsing the Web, then you use domain name servers without even realizing it. Domain name servers, or DNS are an incredibly important but completely hidden part of the internet, and they are fascinating. The DNS system forms one of the largest and most active distributed databases on the planet. Without DNS, the internet would shut down very quickly.
In this article, we’ll take a look at the DNS system so you can understand how it works and appreciate its amazing capabilities. When you use the Web or send an e-mail message, you use a domain name to do it. For example, the URL http://www.google.com contains the domain name google.com. Human-readable names like “CMS.com” are easy for people to remember, but they don’t machines any good. All of the machines yse names called IP addresses to refer to one another. For example, the machine that human refer to as www.google.com has the IP address 192.168.0.24. Every time you use a domain name, you use the Internet’s domain name servers (DNS) to translate the human-readable domain name into the machine-readable IP address. During a day if browsing and e-mailing, you might access the domain name servers hundreds of times!
Domain name servers translate domain name to IP addresses. That sounds like a simple task, and it would be—except for five things:
- There are billions of IP addresses currently in use, and most machines have a human-readable name as well.
- There are many billions of DNS requests made every day. Single person can easily make a hundred or more DNS requests a day, and there are hundreds of millions of people and machines using the Internet daily.
- Domain names and IP addresses change daily.
- New domain names get crated daily.
- Millions of people do the work to change and add domain names and IP addresses every day.
The DNS system is a database is database and no other database on the planet gets this many requests. No other database on the planet has millions of people changing it every day, either. That is what makes the DNS system so unique.
IP addresses:
To keep all of the machines on the internet straight, each machine is assigned a unique address called an IP address. IP stands for Internet Protocol and these addresses are 32-bit numbers normally expressed as four “octets” in a “dotted decimal number”. A typical IP address looks like this: 192.168.0.24.
The four numbers in an IP address are called octets because they can have values between 0 and 256 (28 possibilities per octet).
Every machine on the Internet has its own IP address. A server has a static IP address that does not change very often. A home machine that is dialing through a modem often has an IP address that is assigned by the IPS when you dial in. That IP address is unique for your session and may be different the next time you dial in. In this way, as ISP only need one IP address for each modem it, supports , rather than for every customer.
If you are working on a windows machine, you can view your current IP address with the command WINIPCFG.EXE (IPCONFIG.EXE FOR WINDOWS 2000/XP). On a UNIX machine, type nslookup along with a machine name. (Such as “nslookup http://www.google.com/”) to display the IP address of the machine. (Use the command hostname to learn the name of your machine) As far as the Internet’s machines are concerned, an IP address is all that you need to talk to a server. For example, you can type in your browser the URL http://192.168.0.24 and you will arrive at the machine that contains the Web server for google. Domain names are strictly a human convenience.
Structure of Domain Name System (DNS)
The structure of DNS is similar to the structure of UNIX file system. It is a tree-like structure in which the root is known as the Root DNS server. Each node in the tree is associated with a resources record which holds the information associated with it, and can have any number of branches. There can be a maximum of 127 levels in a tree; however, you will never find any domain name that long. Each node in a tree represents its part in a domain name which can contain a maximum of 63 characters long.
The full domain name of any node in the tree is the sequence of each node in that path from the node to the root. Domain name is read from the node to the with a dot placed separating the names in the path. No two nodes can have the same name if and only if they have the same parent. This guarantees that each domain name in the DNS tree corresponds to unique domain name in the entire DNS structure. E.g. you cannot have two directories named “Program Files” in your C drive root directory, but if you wish you can have a directory name “Program File” in your C drive root directory and another directory of that name in your “Windows” directory.
“A domain is simply a sub tree of the domain name space. The domain name of a domain is the same as the domain name of the node at the very top of the domain. ”
Structure of sjsu.edu domain
As you can see in the figure above that the “sjsu” domain is a part of the edu domain. In the similar fashion there can be many domains.”Any domain name in the sub tree is considering a part of the domain. Because a domain name can be in many sub trees, it can be in many domains.”
Structures of Sub domain (Domain under domain)
After going through all these stuffs the very first question arises: if there are domains inside a domain, then where are all the hosts? If you would remember we had discussed earlier that the domain names are indexed into DNS. A domain may have a single host or a collection of host. Hosts are connected logically and may disperse to geographical locations. You may have 100 hosts connected to same domain that are located in different network too. Usually, the leaves in the tree represent hosts and may point to single network address, hardware information, and mail routing information. The interior nodes of the tree that represent a host on the network. E.g. In the above fog.sjsu.edu can be both ‘San Jose State University domain’ and also the name of the host (more specifically a web server) that run that domain.
Domain Name Servers
Great blog nice n useful information.
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