DNS [Domain Name System] tutorials

When you install a computer, you assign the computer a name. This name is used as the computer’s NETBIOS (Network Basic Input/Output System) name and as the computer’s DNS hostname.
In Windows NT 4.0 network WINS was used to resolve NETBIOS name. on Windows 2000 and later OS, DNS is used to resolve Name Resolution. i.e. resolve DNS Hostname to IP Address and Vice versa.
When the network is not fully configured for DNS name resolution, NETBIOS is required and service called “Computer Browser” is enabled by default in Windows XP and Windows 2003.

Item	Problem
Mac Address	it is 6 byte (48 Bits) Hex-Decimal number and is very difficult to remember. For e.g. 00-07-95-51-9E-6F
IP Address (Binary)	It is 32 Bits Binary number containing 1 and 0 and still very difficult to remember. For e.g. 11000000.10101000.00000001.00000001
IP Address (Decimal)	It is 4 numbers separated by dots. Still difficult to remember for e.g. 192.168.1.1
FQDN	It stands for Fully Qualified Domain Name. Relatively easier to remember and commonly used. For e.g. www.google.com, www.cbtsam.com

Long back when internet was evolved it used to be “Urbannet”. Only one university was responsible for keeping track of host. So there used to be list of computers with its IP address and in each computer there used to be text file named “HOSTS”.
Today with millions and millions of computers and hosts it became unmanageable with just single text file. So the concept of DNS was derived.

Steps involve to resolve IP address

On Client PC, it first check Local DNS cache. i.e. have to gone for that website recently or have you hooked up that IP address recently.
Secondly it check “Hosts” txt file. It is in %systemroot%\System32\Driver\etc folder. This file contains the mappings of IP addresses to host names. Each entry should be kept on an individual line. The IP address should be placed in the first column followed by the corresponding host name. The IP address and the host name should be separated by at least one space. Today however this is not used.
Next it forward query to DNS server of ISP (Internet Service Providers) , which will be checked in forward lookup zone. Now ISP DNS server check it as follow
It checks with internal Local DNS cache
It checks with “Hosts” file
If that web site is on ISP DNS server (i.e. Authoritative zone), most time no.
If it can’t find appropriate record, then it forward query to upstream ISP -DNS, which in turn will do 1,2,3 process again
It check with top level [TLDS] Top Level DNS server [called Root Hints] which in turn gives IP address of .com.dns server or .org.dns server and that finally from there we will get IP address of site required.
Once our ISP DNS server will get IP address, it transfer you to site you want to surf thereafter.

You can clear client’s resolve cashe by typing

Start – run – cmd - ipconfig /flushdns

You can force a client to register its DNS record by typing
Start – run – cmd – ipconfig /registerdns
DNS client send name resolution queries to DNS server using 2 types of lookups:
FORWARD LOOKUP is used to determine IP address of computer from host name (FQDN)
REVERSE LOOKUP: Is used to determine Host name (FQDN) from its IP address

When DNS client receive a query response from DNS server, the response is stored in the local DNS resolver cache. To check it type
Start – run – cmd – ipconfig /displaydns
This will display number of records along with time to expire. Time to Live will display value that represents Seconds until which the resolver cache entry expires.

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Windows Server 2008

DNS [Domain Name System] tutorials

When you install a computer, you assign the computer a name. This name is used as the computer’s NETBIOS (Network Basic Input/Output System) name and as the computer’s DNS hostname.

In Windows NT 4.0 network WINS was used to resolve NETBIOS name. on Windows 2000 and later OS, DNS is used to resolve Name Resolution. i.e. resolve DNS Hostname to IP Address and Vice versa.

When the network is not fully configured for DNS name resolution, NETBIOS is required and service called “Computer Browser” is enabled by default in Windows XP and Windows 2003.

Item

Problem

Mac Address

it is 6 byte (48 Bits) Hex-Decimal number and is very difficult to remember. For e.g. 00-07-95-51-9E-6F

IP Address (Binary)

It is 32 Bits Binary number containing 1 and 0 and still very difficult to remember. For e.g. 11000000.10101000.00000001.00000001

IP Address (Decimal)

It is 4 numbers separated by dots. Still difficult to remember for e.g. 192.168.1.1

FQDN

It stands for Fully Qualified Domain Name. Relatively easier to remember and commonly used. For e.g. www.google.com, www.cbtsam.com

Long back when internet was evolved it used to be “Urbannet”. Only one university was responsible for keeping track of host. So there used to be list of computers with its IP address and in each computer there used to be text file named “HOSTS”.

Today with millions and millions of computers and hosts it became unmanageable with just single text file. So the concept of DNS was derived.

Steps involve to resolve IP address

On Client PC, it first check Local DNS cache. i.e. have to gone for that website recently or have you hooked up that IP address recently.

Next it forward query to DNS server of ISP (Internet Service Providers) , which will be checked in forward lookup zone. Now ISP DNS server check it as follow

It checks with internal Local DNS cache

It checks with “Hosts” file

If that web site is on ISP DNS server (i.e. Authoritative zone), most time no.

If it can’t find appropriate record, then it forward query to upstream ISP -DNS, which in turn will do 1,2,3 process again

It check with top level [TLDS] Top Level DNS server [called Root Hints] which in turn gives IP address of .com.dns server or .org.dns server and that finally from there we will get IP address of site required.

Once our ISP DNS server will get IP address, it transfer you to site you want to surf thereafter.

You can clear client’s resolve cashe by typing

Start – run – cmd - ipconfig /flushdns

You can force a client to register its DNS record by typing

Start – run – cmd – ipconfig /registerdns

DNS client send name resolution queries to DNS server using 2 types of lookups:

FORWARD LOOKUP is used to determine IP address of computer from host name (FQDN)

REVERSE LOOKUP: Is used to determine Host name (FQDN) from its IP address

When DNS client receive a query response from DNS server, the response is stored in the local DNS resolver cache. To check it type

Start – run – cmd – ipconfig /displaydns

This will display number of records along with time to expire. Time to Live will display value that represents Seconds until which the resolver cache entry expires.