What is Imprtant of DNS Distributed, Hierarchical Database

DNS Distributed, Hierarchical Database solve the below problems 
A single point of failure:- If the DNS server crashes, so does the entire Internet!

Traffic volume:- A single DNS server would have to handle all DNS queries (for all the HTTP requests and e-mail messages generated from hundreds of millions of hosts).

Distant centralized database:-A single DNS server cannot be “close to” all the querying clients. If we put the single DNS server in New York City, then all queries from Australia must travel to the other side of the globe, perhaps over slow and congested links. This can lead to significant delays.

Maintenance:-The single DNS server would have to keep records for all Internet hosts. Not only would this centralized database be huge, but it would have to be updated frequently to account for every new host

DNS - Other important services in addition to translating hostnames to IP addresses

Host Aliasing

• Host with a complicated hostname can have one or more alias names. For example, a hostname such  as relay.ex1-test.example.com
• Then in this example host has  two aliases such as example.com and www.example.com. 
• In this case, the hostname relay.ex1-test.example.com is said to be a canonical hostname. Alias hostnames, when present, are typically more mnemonic than canonical hostnames.
• Then we typed example.com or www.example.com in the browsers it map to same server 82.166.201.163

You can do simple exercise using packet tracer shown go through  link

Creatiing the Network using DHCP server, HTTP Server, DNS server and PC with Packet tracer simulator

Mail server aliasing

Above obvious reasons  e-mail addresses also be mnemonic. For example, if Bob has an account with Hotmail, Bob’s e-mail address might be as simple as bob@hotmail.com. 

However, the hostname of the Hotmail mail server is more complicated and much less mnemonic than simply hotmail.com (for example, the canonical hostname might be something like relay1.west-coast.hotmail.com). 
DNS can be invoked by a mail application to obtain the canonical hostname for a supplied alias hostname as well as the IP address of the host.

Load distribution.

 DNS is also used to perform load distribution among replicated servers, such as replicated Web servers. Busy sites, such as cnn.com, are replicated over multiple servers, with each server running on a different end system and each having a different IP address. 
For replicated Web servers, a set of IP addresses is thus associated with one canonical hostname.
The DNS database contains this set of IP addresses. When clients make a DNS query for a name mapped to a set of addresses, the server responds with the entire set of IP addresses, but rotates the ordering of the addresses within each reply. Because a client typically sends its HTTP request message to the IP address that is listed

you can find the all the IP address for one canonical name tiring below example. 
 How to find the all the ip adddress for one domain name

How to find the all the ip adddress for one domain name

Busy sites, such as cnn.com, are replicated over multiple servers, with each server running on a different end system and each having a different IP address. 

For replicated Web servers, a set of IP addresses is thus associated with one canonical hostname.

In this session shows how to find the all the ip address for one canonical host name in the linux os

As a example try to find the all the ip address for www.google.com, it's mean replicated servers for www.google.com

first we have to find the one ip address for www.google.com (using ping cammand)
 
$ ping www.google.com
PING www.google.com (194.90.196.121) 56(84) bytes of data.
64 bytes from 194.90.196.121: icmp_seq=1 ttl=128 time=256 ms
64 bytes from 194.90.196.121: icmp_seq=2 ttl=128 time=224 ms
64 bytes from 194.90.196.121: icmp_seq=3 ttl=128 time=252 ms
64 bytes from 194.90.196.121: icmp_seq=4 ttl=128 time=259 ms
64 bytes from 194.90.196.121: icmp_seq=5 ttl=128 time=226 ms


after that using whois command to find the origin 

whois -h whois.radb.net  194.90.196.121
 

after that type this command to find the all the ip address using origin AS1680
whois -h whois.radb.net '!gAS1680'

Creatiing the Network using DHCP server, HTTP Server, DNS server and PC with Packet tracer simulator

• Create following network using Packet Tracer simulator

•  Configure Router  

A router is a device that determines the next network point to which a packet should be forwarded toward its destination.
You can do simple exercise using packet tracer shown go through  link to configure Router
How to configure router with packet tracer simulater  

•  DHCP Server Configuration

Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway.
 
You can do simple exercise using packet tracer shown go through  link to configure DHCP server
DNS Configuration with Packet Tracer in GUI

•  DNS Server Configuration

The most important function of DNS servers is the translation (resolution) of human-memorable domain names and hostnames into the corresponding numeric Internet Protocol (IP) addresses. 
 

 You can do simple exercise using packet tracer shown go through  link to configure DNS Server

DNS Configuration with Packet Tracer in GUI

• HTTP Server Configuration

A web server(http server) is an information technology that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide 

You can do simple exercise using packet tracer shown go through  link to configure HTTP Server
 Web server Configuration with Packet Tracer in GUI 


After that you can access the web site in the PC using browser typing ip address 192.168.1.50

Web server Configuration with Packet Tracer in GUI

A web server(http server) is an information technology that processes requests via HTTP, the basic network protocol used to distribute information on the World Wide 

In this session show how to host the web site in the web server not conceptually but cat get very simple idea using in packet tracer.

1st set the ip address to dhcp server  192.168.1.50 255.255.255.0
double click server -> config -> fastethernet0 -> set static IP address 192.168.1.50 and subnet mask 255.255.255.0 

Create a simple index.html page in the http server to access for user. 

The html  simple source code  is hear

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" type="text/css" href="style.css" />
<title>THIS IS TESTING PAGE</title>
</head>
<body>
    <div id="page">
                <div id="header">
                    <img src="logo.png" alt="XHTML Template by Bryant Smith" />
                    <!-- Include an <h1></h1> THIS IS TESTING PAGE -->
                </div>
                    </div>
                <div id="content">
                    <div id="container">

                        <div id="main">
                        <div id="menu">
                            <ul>
                                <li><a href="#">Contact</a></li>
                                <li><a href="#">About</a></li>
                                <li><a href="#">Services</a></li>
                                <li><a href="#">Gallery</a></li>
                                <li><a href="#">Portfolio</a></li>
                                <li><a href="#">Home</a></li>
                            </ul>
                        </div>
                        <div id="text">
                               <h1>THIS IS TESTING PAGE</h1>
                            <p>Blue Micro is meant for a site that doesn't necessarily need a huge amount of content.  I've found that trying to put a small amount of text onto a large template ends up in a site that looks slightly off.  So this template is for those that need a quick and simple site</p>
                           
                            <h1>THIS IS TESTING PAGE</h1>
                            <p>Try to include your keywords in the titles since they are what seach engines pick up, it's also a good idea to try to include those same keywords in the title as well (only one of two of your best ones).</p>
                            <h1>THIS IS TESTING PAGE</h1>
                          <p>I debated using a fancy background for this template, but ultimately just decided to keep it blank. I did however create all the images with Alpha transparency, which means that regardless of what background you choose, it will always look good. So keep it white, or experiment with it if you please.</p>
                            <h1>THIS IS TESTING PAGE</h1>
                            <p>This template validates as XHTML 1.1 - this is to ensure it'll work for many years to come, and it makes it really easy for you to modify.</p>
                            <p>Try to include your keywords in the titles since they are what seach engines pick up, it's also a good idea to try to include those same keywords in the title as well (only one of two of your best ones).</p>
                       
                                                
                        </div>

                        </div>
                </div>
                <div class="clear"></div>
                <div id="footer">
                    <p><a href="http://www.bryantsmith.com/template">free xhtml template</a> by <a href="http://www.bryantsmith.com">web page designer</a></p>
                </div>
         
        </div>
    
</body>
</html>

Copy and paste simple html cord in the index.html page  
After that you can access the web site in the PC using browser tying ip address 192.168.1.50

 

DNS Configuration with Packet Tracer in GUI

The most important function of DNS servers is the translation (resolution) of human-memorable domain names and hostnames into the corresponding numeric Internet Protocol (IP) addresses. 

It is used bunch of records to do these things such as NS records,CNAME, TXT ,A records etc. these bunch of records details are stored in db file according to the domain.

In this exercise we can get brief idea of these records but it is not actual one in the DNS server. 

1st set the IP address to the DNS server 
double click server -> config -> fastethernet0 -> set static IP address 192.168.1.3 and subnet mask 255.255.255.0

 Add a records to the DNS server

In this example the host 192.168.1.50  www.testingpage.com use aliasing name such as mytesting and testing.com. These alias name enter as CNAME records in to the DNS server in the db file. Then enter the A record for the  www.testingpage.com.

mytesting CNAME www.testingpage.com

testing.com CNAME www.testingpage.com

www.testingpage.com A record 192.168.1.50 

 Then we can use host name www.testing.com to mytesting,and testing.com in the browser

DHCP Server Configuration with packet tracer in GUI

Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway.

In this session show how to set the ip pool to dhcp server using GUI with packet tracer.   

1st set the ip address to dhcp server  192.168.1.3 255.255.255.0

then set the ip pool in to the DHCP server

type the pool name: serverpool
 Default gatway:192.168.1.1
DNS server ip address:192.168.1.2
start ip address :192.168.1.0
subnet mask : 255.255.255.0
maximum number of users: 256

After that DHCP server connect to the switch and create a network as bellow .

After that set the option ip address dynamically in the PC

 

How to configure router with packet tracer simulater

The router has  usually few modes to do some particular activities in each mode. There are  User Exec Mode ,Privileged Mode and Global Configuration Mode     

User Exec Mode (distinguished by the ">" prompt) is your first mode and it is also called enable mode , which is used to get statistics from router.

Router>?
Exec commands:
  <1-99>      Session number to resume
  connect     Open a terminal connection
  disable     Turn off privileged commands
  disconnect  Disconnect an existing network connection
  enable      Turn on privileged commands
  exit        Exit from the EXEC
  logout      Exit from the EXEC
  ping        Send echo messages
  resume      Resume an active network connection
  show        Show running system information
  ssh         Open a secure shell client connection
  telnet      Open a telnet connection
  terminal    Set terminal line parameters
  traceroute  Trace route to destination

Privileged Mode (distingushed by the "#" prompt) is the second mode. Here you can enable or disable interfaces on the router, get more detailed information on the router, To come to privileged mode  type the "enable" command in the user mode.

 Router>enable

 Router#

Global Configuration Mode (distingushed by the (config)# prompt) is accessable via Privileged Mode. In this mode you're able to configure each interface individually, 

•  setup banners and passwords,
•  enable secrets (encrypted passwords), 
•  enable and configure routing protocols 
• etc...

We dare say that almost everytime you want to configure or change something on the router, you will need to be in this mode.

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#


there are steps which shows how to configure  a router 

Router>enable                                                                   //user mode
Router#configure terminal                                             //Privileged Mode
Router(config)#interface fastEthernet 0/0                 //global config Mode
                                                                                                                             select the port
 
Router(config-if)#ip address 192.168.1.1 255.255.255.0
 //set the IP address and mac address

Router(config-if)#no shutdown
Router(config-if)#ex
Router(config)#ex
or

 

What happens when a browser requests the URL

DNS is commonly employed by other application-layer protocols—including HTTP, SMTP, and FTP—to translate user-supplied hostnames to IP addresses. 

• As an example, consider what happens when a browser (that is, an HTTP client), running on same user’s host, requests the URL www.dialog.lk/index.html.

• In order for the user’s host to be able to send an HTTP request message to the Web server www.dialog.lk, the user’s host must first obtain the IP address of www.dialog.lk. This is done as follows.

Why we need Domain Name System

Human can identified using birth certificate name, National Identity card numbers, driving license numbers. But my entire friend identified me with my birth certificate name because more mnemonic birth certificate names rather than National Identity card number.

indeed, can you imagine saying,

 Just as humans can be identified in many ways, so too can Internet hosts. One identifier for a host is its hostname. Hostnames—such as www.google.lk, www.yahoo.com, gaia.cs.umass.edu, and cis.poly.edu—are mnemonic. However, hostnames provide little, if any, information about the location within the Internet of the host. (A hostname such as www.dialog.lk, which ends with the country code .lk, tells us that the host is probably in Sri Lanka, but doesn’t say much more.) Furthermore, because hostnames can consist of variable length alphanumeric characters, they would be difficult to process by routers. For these reasons, hosts are also identified by so-called IP addresses.

An IP address is hierarchical because as we scan the address from left to right, we obtain more and more specific information about where the host is located in the Internet (that is, within which network, in the network of networks). Similarly, when we scan a postal address from bottom to top, we obtain more and more specific information about where the addressee is located.

We have just seen that there are two ways to identify a host—by a hostname (www.dialog.lk) and by an IP address(123.234.65.79). People prefer the more mnemonic hostname identifier, while routers prefer fixed-length, hierarchically structured IP addresses. In order to reconcile these preferences, we need a directory service that translates hostnames to IP addresses. This is the main task of the Internet’s domain name system (DNS).