Archive for January, 2008


What and Why for DNS…

What is DNS (Domain Name system):
DNS is the system to host domain names (e.g.,, resolve them to IP addresses(or reversely) and tell the computer where to look for the resources (file, web pages, mp3).

Why we need DNS (Domain name system):
There are 3 type of addresses used to identify a PC (including main frames, server arrays, PDA, mobile phone who all operated under TCP/IP protocol):
MAC address: static and unique address associated with every network interface hardware (e.g. 00-02-72-D1-61-1B).
To find out your MAC address, type ipconfig /all at command prompt(Windows)
or ifconfig in linux command shell.
These addresses are basically hex value and merely identify the hardware (and their vendors). In order for the use of network infrastructure designing (subnetting, NAT, PAT, routing etc), we come to next address.
IP address: It is very well known especially addresses started with 192.168.1.x and 10.0.x.x. To see your own IP address, type the commands above again and you will get it.
Domain Name: Here come the case, is hosted at server with IP address and web page is hosted at IP address You are not able to (and you don’t have to) remember these boring numbers in order to access the webpage.

But computers are running on 0/1 and can’t under what is It will ask ‘someone‘ what IP address is associated with Thus DNS is the ‘someone’!

Simplest DNS concept:
When a computer doesn’t know where to request the resources (web pages, file, songs etc), it will ask DNS server. Records are stored in DNS server for queries.  As this is the simplest introduction, I only state 2 type of record:
‘A’ record: It is IP address associated with domain name. (e.g. associated with When ‘’ is typed in Internet browser, the computer will automatically get this A record from DNS. Doing a A record query is referred as Forward Lookup.
‘PTR’ record: It is an domain name associated with IP address. (e.g. associated with It is referred as Reverse Lookup and it is not commonly used.

So, it is actually a information exchanges on two entities: IP address(es) <==> Domain Name(s).

To do a forward lookup manually
Example: Domain name:      IP address:,
In Windows command prompt, type nslookup <domain name> <name server, more often your router IP, eg., etc>

In Linux command shell, type dig  a <domain name>

To do reverse lookup manually
In Windows command prompt, type nslookup <IP address> <ame server, more often your router IP, eg., etc.>
In Linux command shell, type dig -x <IP address>