01 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 card number, AAdhar card number. You know that how much these numbers are important.
How our letter reaches to our address? First it comes to main GPO 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. How your machine can be recognised on the network or Internet? One solution is to write name on monitor by marker pen or otherwise at the time of installation you can give name to system. But how other machine would recognise your machine?
Network card manufacturers provide physical address in the network card of your machine. If we are using Ethernet technology then your card is having 48 bit Ethernet address. How to find this physical address of your machine? First check that your machine is having physical card. This you can check for RJ-45 connector on the back panel of your machine. You can run following command in the Windows platform:
| C:\>ipconfig /all
Windows 2000 IP Configuration
Host Name . . . . . . . . . . . . : ibm1 Primary DNS Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Broadcast IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Local Area Connection 2:
Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Realtek RTL8139(A)-based PCI Fast Ethernet Adapter Physical Address. . . . . . . . . : 00-08-A1-32-74-AD DHCP Enabled. . . . . . . . . . . : No IP Address. . . . . . . . . . . . : 172.16.3.254 Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . : 172.16.0.240 DNS Servers . . . . . . . . . . . : |
Fig 1 Output of IPconfig command (This output can change on your machine, it depends on operating system you are working, eg Windows7,8 or XP)
In the above output other details like subnet mask, IP address are there. But we will study them later. Physical address of my network card or my computer is 00-08-A1-32-74-AD.
On the Linux machine give following command to know the physical address of your network card:
You should be root user to get these details.
| # ifconfig -eth0
Link encap:Ethernet HWaddr 00:80:AD:73:F7:E2 inet addr:172.16.3.1 Bcast:172.16.255.255 Mask:255.255.0.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1968977 errors:1 dropped:0 overruns:0 frame:1 TX packets:526 errors:48 dropped:0 overruns:0 carrier:48 collisions:1 txqueuelen:100 RX bytes:122462650 (116.7 Mb) TX bytes:54807 (53.5 Kb) Interrupt:22 Base address:0x3000 |
Fig 2 output of ifconfig command on Linux platform
Here physical address is 00:80:AD:73:F7:E2 You can say that I use different computer to run this command.
Packets reach to your machine from other machine by mentioning this physical address in the Ethernet frame.
| preamble | 48 bit | data portion |
physical address
Fig 3 Ethernet packet
2 Why physical address is not sufficient on the Internet?
