1 Introduction
As many people have name like “Ramesh”, “Ram”, we are used to call these guys by name. We can give numbers also to these people. These people get numbers as PAN number, which is used by Income tax department for assessment. They have Aadhar card number. We are mapping one identity with other identify. How we can give number to our computer also so that packet should come from internet to our computer.
How our letter reaches to our address? First it comes to main GPO (General post office) then to region wise post offices and only our area postman knows our address. He physically carries letters to our home. Similarly we can hire post-box number if mailing is heavy or want to protect our identity. These are all to recognise you. In same way we can receive data packets from Web Server to our computer.
How your computer can be recognised on the network or Internet? One solution is to write your name on monitor by marker pen or otherwise at the time of installation you can give name to system. But how other computer would recognise your computer? This is not simple if there are million computers are connected on the Internet and people are searching www.engineersgarage.com web site.
Network card manufacturers provide physical address in the network card of your computer. If we are using Ethernet technology then your card is having 48 bit Ethernet address. How to find this physical address of your computer? First check that your computer is having physical card or RJ45 connector on the back panel of your mother board of your computer.. This you can check for RJ-45 (this look like telephone Jack ) connector on the back panel of your computer. You can run following command in the Windows platform. You click on start button of operating system and then check on Run button and type cmd command to open command shell. Then type below command.
Fig. 1: Picture Showing IPConfig Command Output on Windows Operating System to understand Computer Networking
You can check physical address of my computer is F4-6D-04-15-C2-05
This is address is unique which is coming from LAN card or Ethernet controller of my motherboard.
2 Why physical address of my computer is not sufficient on the Internet?
If physical address is available in the every network card and it is unique also then why we need IP address? You just imagine that there is problem in the hotmail.com server’s network card and they are replacing their network card by new card; when they change network card, the physical address of hotmail.com is changed, do you think that server should report to 50 million computers that its physical address is changed, assuming that 50 million hits are there on hotmail.com server? This is impossible!!!!! This is reason why physical address is not sufficient on Internet communication.
When you go in the cyber café, did you bother for physical address of hotmail.com, indiatimes.com server? Never! Because you are interested in the mailbox opening and you want to consume total Rs. 25, which you are going to pay to cyber café owner after one hour. You do not worry for physical address of hotmail.com. You do not worry for the IP address also. You just type “www.hotmail.com” in browser window and you get your mailbox. That’s it!!!
DNS (Domain Name System) protocol will take care of your “www.hotmail.com” string; it will supply “IP” address of hotmail.com to your browser. DNS(Domain Name System) protocol is working on application layer and which create query packet to resolve “website name” with its IP address from DNS Server. DNS Server are computers scattered all over world for this job. Your browser will use this “IP” address to form packet. Now you understand use of “IP” address. IP address is nothing but logical address only. Now how to check IP address of your computer? You can use same command of fig 1 ipconfig. Otherwise check network neighbourhood properties. You will find following IP address:
IP address: 192.168.0.2
Subnet mask: 255.255.255.0
This is logical address of your computer. We are calling this as logical address because we can modify using “networking properties” in the control panel. But if I removed my hard disk then, my computer’s IP address has gone! Because operating system keep IP address in the hard disk. So we can say when no hard disk, no IP Address. Is it possible to send packets to other computer without IP address? Yes, provided your computer should get “IP” address from server. This server should run “DHCP”( Dynamic Host Configuration Protocol) services. Here DHCP is giving temporary IP address to your computer system. This is happening when you take Internet connection from MTNL, BSNL or Hathway cablenet kind of service providers. One more thing is visible below IP address, which is Subnet mask. This mask use to separate IP address of computer and Network address.But remember operating system of your computer maintains “IP” address. Address is 32-bits in the IP version four and 128-bits in the IP version six. This 32 bit address can be classified into three parts: class definition + netid + hostid.
0 1 7 8 31
|
0 |
7 bit |
|
|
|
class netid hostid(24 bits)
definition
Class A: definition
Now we have physical address and IP address on your computer. Netid is useful part for network. Here we are assuming computer is connected in the network in various topologies like Star, bus, and Ring. Your computer uses both. This is not right explanation, if you are browsing Internet from home as a dial-up service via telephone line using ASL modem. In that case your computer uses point-to-point protocol.
3 Why physical and IP addresses are not sufficient on Internet?
Your computer is running operating system and this OS is multitasking. You open four browser windows at a time. When you go in the cyber café, you want to consume all Rs. 15 which you are paying to cyber café owner. You start hotmail.com, then indiatimes.com, then rediffmail.com. Have you seen that your rediffmail mail account is opened in the hotmail? No, why? Because ports are separating these two mailbox traffic.
We will take an example; say there is one server computer, on this server different application such as telnet, FTP, TFTP servers are running. Here server means softwares that are running on single computer Operating system is handling these processes. See following diagram.
Fig. 2: Image Showing Last Address on Application Servers
In the fig 3, all datagrams, which are reaching to server, have same destination IP address. That’s why all packets reached to this computer. But once these packets are at IP layer, now port number separates segments of telnet, FTP, SMTP. Port number is 16 bit number. There is 1 to 65535 port number. Some port numbers are having fixed function, they are called Well-known port number and some are private port numbers which can be purchased by Third Party Company and assigned for particular services. Maximum port numbers are temporary which are assigned time to time for Internet sessions and destroy one work is over.
You type c:>netstat command in the command prompt to check port numbers. When my computer was not connected with http://www.engineersgarage.com using Internet, my computer shows typical port numbers. Fig 4 shows output of Netstat command when heavy website is not opened on your computer.
Fig. 3: Image Showing TCP Port Numbers and Services Visible as Established Status/State
I have done small experiment and type http://www.engineersgarage.com website in the chrome or IE or Mozilla web browser. Then I typed c:>netstat command. You will get wonderful details of port numbers and various services opened on the background of operating system. Fig 5 shows output of those services. This way you can learn various networking activities happening in your computer. Command prompt commands are very helpful for that.
Fig. 4: Picture Showing Computer Receiving Port Number from Other Website
Fig. 4 shows very interesting part also. Some data is coming from Akamaitechnologies website also.
We know that Akamai is Mirror website service provider.
Lets now explore how to track intermediate router in between your PC and your favorurite website. I want to find out how network packets originated from my PC travel to the google.com
You have to type c:>tracert www.google.com
When you type this command on your computer, may be some thing different will come. Fig 6 show what I got in between my PC and www.google.com. First column shows serial number and second coloum shows Delay between my PC and google.com
This out put show almost 17 “points of transmission” are there in between my PC and www.google.com. Packet originated from my PC 192.168.0.2 and it is going thorugh default gatway which is 192.168.0.1 then my TCP segment (packet) move to IP address 125.99.88.9 Now I donot know where this IP address located. To find out where this IP address is situated, you can use following website
You open this website and provide 125.99.88.9 in one windows of this website. I got Fig 7. You can noticed that I am using Hathway Cable net and it is situated in Mumbai, Maharashtra State
Fig. 5: Image Showing Tracert Command Output for www.google.com
Fig. 6: Output Offered by www.ipolocation.net
In this way you can find out geolocation of last webserver. You try out this experiments with networking commands. Please share your experience on our website. Happy reading!!!
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