Introduction of MAC Address in Computer Network

03 Jun, 2022
In order to communicate or transfer the data from one computer to another computer, we need some address. In Computer Network various types of addresses are introduced; each works at a different layer. Media Access Control Address is a physical address that works at the Data Link Layer. In this article, we will discuss about addressing DLL, which is MAC Address. 
MAC Addresses are unique 48-bits hardware number of a computer, which is embedded into a network card (known as a Network Interface Card) during the time of manufacturing. MAC Address is also known as the Physical Address of a network device. In IEEE 802 standard, Data Link Layer is divided into two sublayers – 
Logical Link Control(LLC) SublayerMedia Access Control(MAC) Sublayer
Logical Link Control(LLC) Sublayer
Media Access Control(MAC) Sublayer
MAC address is used by the Media Access Control (MAC) sublayer of the Data-Link Layer. MAC Address is worldwide unique since millions of network devices exist and we need to uniquely identify each. 
 
MAC Address is a 12-digit hexadecimal number (6-Byte binary number), which is mostly represented by Colon-Hexadecimal notation. The First 6-digits (say 00:40:96) of MAC Address identifies the manufacturer, called OUI (Organizational Unique Identifier). IEEE Registration Authority Committee assigns these MAC prefixes to its registered vendors. 
Here are some OUI of well-known manufacturers :
CC:46:D6 - Cisco 
3C:5A:B4 - Google, Inc.
3C:D9:2B - Hewlett Packard
00:9A:CD - HUAWEI TECHNOLOGIES CO.,LTD
The rightmost six digits represent Network Interface Controller, which is assigned by the manufacturer. 
As discussed above, the MAC address is represented by Colon-Hexadecimal notation. But this is just a conversion, not mandatory. MAC address can be represented using any of the following formats:
Note: Colon-Hexadecimal notation is used by Linux OS and Period-separated Hexadecimal notation is used by Cisco Systems.  
Command for UNIX/Linux -  ifconfig -a
                          ip link list 
                          ip address show

Command forWindows OS -   ipconfig /all 

MacOS -                   TCP/IP Control Panel
Note – LAN technologies like Token Ring, and Ethernet use MAC Addresses as their Physical address but there are some networks (AppleTalk) that do not use MAC addresses. 
1. Unicast: A Unicast addressed frame is only sent out to the interface leading to a specific NIC. If the LSB (least significant bit) of the first octet of an address is set to zero, the frame is meant to reach only one receiving NIC. MAC Address of source machine is always Unicast. 
2. Multicast: The multicast address allows the source to send a frame to a group of devices. In Layer-2 (Ethernet) Multicast address, LSB (least significant bit) of the first octet of an address is set to one. IEEE has allocated the address block 01-80-C2-xx-xx-xx (01-80-C2-00-00-00 to 01-80-C2-FF-FF-FF) for group addresses for use by standard protocols. 
3. Broadcast: Similar to Network Layer, Broadcast is also possible on the underlying layer( Data Link Layer). Ethernet frames with ones in all bits of the destination address (FF-FF-FF-FF-FF-FF) are referred to as the broadcast addresses. Frames that are destined with MAC address FF-FF-FF-FF-FF-FF will reach every computer belonging to that LAN segment. 
Some ISPs use MAC addresses in order to assign an IP address to the gateway device. When a device connects to the ISP, the DHCP server records the MAC address and then assigns an IP address. Now the system will be identified through the MAC address. When the device gets disconnected, it loses the IP address. If the user wants to reconnect, the DHCP server checks if the device is connected before. If so, then the server tries to assign the same IP address (in case the lease period has not expired). In case user changed the router, the user has to inform the ISP about new MAC address because the new MAC address is unknown to ISP, so the connection cannot be established. 
Or the other option is Cloning, user can simply clone the registered MAC address with ISP. Now router keeps reporting the old MAC addresses to ISP and there will be no connection issue. 
Media Access Control address (MAC address) is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification and used in the Media Access Control protocol sub-layer.An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits (4 bits per hexadecimal digit). MAC addresses are in a flat structure and thus they are not routable on the Internet. Serial interfaces do not use MAC addresses. It does NOT contain a network and host portion with the address. It is used to deliver the frame to the destination device.
hobbitakhilesh
romim256
Computer Networks
GATE CS
Computer Networks
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