What is MAC Address ??

In a local area network (LAN) or other network, the MAC (Media Access Control) address is your computer's unique hardware number.

In a local area network (LAN) or other network, the MAC (Media Access Control) address is your computer's unique hardware number. (On an Ethernet LAN, it's the same as your Ethernet address.) When you're connected to the Internet from your computer (or host as the Internet protocol thinks of it), a correspondence table relates your

IP address to your computer's physical (MAC) address on the LAN.

The MAC address is used by the Media Access Control sublayer of the Data-Link Layer (DLC) of telecommunication protocols. There is a different MAC sublayer for each physical device type. The other sublayer level in the DLC layer is the Logical Link Control sublayer.

Windows XP, 2000, and NT
 
  Click on the Start Menu then select Run.
   
  Type cmd then click OK.
  
 In the Command Prompt box, type ipconfig /all then hit Enter.
 
  Note : the Physical Address, this is also the MAC address.
   
    Windows ME, 98, and 95

    Click on the Start Menu then select Run.

    Type winipcfg then click OK.

    In the drop down menu, select the item corresponding to your network card (ignore the PPP Adapter).

    Note : the Adapter address, this is the MAC address.
   
    MacOS X

In MacOS 10.2 and newer, there are two methods of finding your computer's MAC address. In versions earlier than 10.2, only the first method is available.

Method 1:

    Go to the Apple Menu

    Select System Preferences

    Select Network

    Be sure that the pulldown list is at Show: Built-In Ethernet

    Select the TCP/IP tab

    The MAC address will be shown as Ethernet Address

Method 2 (works with 10.2 and newer):

    Go to the Apple Menu

    Select About This Mac

    Select More Info

    Select the System Profile tab

    Under Network Overview: Built-In, the MAC address will be shown as Ethernet Address
   
 Linux

   ifconfig -a

  The following is the resulting output. The MAC address appears on the same line as the name of each      device (labeled HWaddr). In this example, eth0 is the name of the device that has a MAC address. lo will not have a MAC address as it is a loop back address only. If you have more than one device connected to the network, it will be listed as well, with a different MAC address.

                eth0 Link encap:Ethernet HWaddr 00:90:27:2A:C4:65

   inet addr:131.215.105.34 Bcast:131.215.105.255 Mask:255.255.255.0
 
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
  
 RX packets:96182694 errors:0 dropped:0 overruns:0 frame:2

 TX packets:137175658 errors:0 dropped:0 overruns:0 carrier:0

   collisions:0 txqueuelen:100

   Interrupt:14 Base address:0x6000

lo Link encap:Local Loopback

    inet addr:127.0.0.1 Mask:255.0.0.0

    UP LOOPBACK RUNNING MTU:3924 Metric:1

    RX packets:5738011 errors:0 dropped:0 overruns:0 frame:0

    TX packets:5738011 errors:0 dropped:0 overruns:0 carrier:0

    collisions:0 txqueuelen:0
     

 Solaris

At the prompt, type arp and the machine name as shown:

                      {shada:2194} arp shada

     shada (131.215.48.53) at 8:0:20:b9:59:e6 permanent published
     

You can generalize this to

                      arp `uname -n`
     

Note : that backticks surround the uname -n command.

SunOS

At the prompt, type ifconfig -a as shown. Note that the MAC address is also called the ethernet address abbrievated to ether by this command.

                accord# ifconfig -a

le0: flags=63

More Details about What A MAC Address Really Is

In order for a device to connect to a network, the device needs to have a unique ID. This ID is similar to a street address for a house; there should be no two devices with the same address. The address is used to send data from one device to another device.

In the case of Ethernet packets, the following information is stored in each data packet on a local network:

    Mac Control -- This contains the protocol control information

    Destination MAC Address -- Where the packet is to be delivered to

    Source MAC Address -- Where the packet is being sent from

    LLC PDU -- The actual data in the ethernet packet

    CRC -- Error detecting code