Introduction of MAC Address in Computer Network

To communicate or transfer data from one computer to another computer, we need some address. In Computer Networks 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 addressing DLL, which is MAC Address. 

Media Access Control Address

MAC Addresses are unique 48-bit 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 – 

1. Logical Link Control(LLC) Sublayer
2. 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. 

Format of MAC Address

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 the MAC Address identify 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.  

How To Find the MAC Address

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. 

Types of MAC Address

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. The MAC Address of the 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, the 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. 

What is MAC Cloning?

Some ISPs use MAC addresses 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 the user changed the router, the user has to inform the ISP about the 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. 

Characteristics of MAC Address

The 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 use 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.

• MAC addresses are used in LAN (Local Area Network) environments to identify devices and allow communication between them.
• MAC addresses are burned into the hardware of a network interface card (NIC) and cannot be changed, except in some rare cases where the manufacturer has provided a specific tool to do so.
• The first 3 bytes of a MAC address represent the manufacturer ID, while the last 3 bytes represent a unique identifier assigned by the manufacturer.
• MAC addresses are often used in conjunction with ARP (Address Resolution Protocol) to resolve IP addresses to MAC addresses for communication on a LAN.
• Some operating systems, such as Windows and Linux, allow you to view the MAC address of your network adapter through a command prompt or network settings.

Advantages

1. Uniqueness: Each MAC address is unique, which means that devices on the network can be easily identified and managed.
2. Simplicity: MAC addresses are easy to configure and manage, and do not require any additional network infrastructure.
3. Compatibility: MAC addresses are widely used and supported by a variety of networking technologies and protocols, making them compatible with many different systems.
4. Security: MAC addresses can be used to restrict access to a network by only allowing devices with authorized MAC addresses to connect.
5. Fault-tolerance: In case of hardware or software failure, a device can be easily replaced without affecting the network, as long as the new device has the same MAC address as the old one.
6. Multicasting: MAC addresses can be used for multicasting, allowing a single packet to be sent to multiple devices at once.
7. Efficiency: MAC addresses allow for efficient communication on the network, as they enable devices to quickly and easily identify and communicate with each other.
8. Lower network overhead: MAC addresses reduce network overhead by allowing devices to communicate directly with each other without the need for additional routing or addressing.
9. Ease of troubleshooting: MAC addresses can be used to troubleshoot network issues by identifying the source of problems and tracking network activity.
10. Flexibility: MAC addresses can be used to support a variety of network configurations and topologies, including peer-to-peer, client-server, and hybrid models.

Disadvantages

1. Limited address space: MAC addresses are 48-bit numbers, which means that there is a finite number of possible MAC addresses. This can lead to address conflicts if multiple devices have the same MAC address.
2. Spoofing: MAC addresses can be easily spoofed, allowing unauthorized devices to gain access to the network.
3. Inefficiency: MAC addresses are not hierarchical, which can make it difficult to efficiently manage large networks.
4. Static addressing: MAC addresses are typically assigned at the time of manufacture and cannot be easily changed. This can be a disadvantage in situations where devices need to be reconfigured or replaced.
5. Limited scope: MAC addresses are only used for identifying devices within a local network segment, and cannot be used to identify devices outside of this segment.
6. Hardware-dependent: MAC addresses are tied to the network interface card (NIC) of a device, which means that if the NIC fails or is replaced, the MAC address also changes.
7. Lack of encryption: MAC addresses are sent in plain text, which can make them vulnerable to interception and eavesdropping.
8. No inherent security: While MAC filtering can be used to restrict access to a network, MAC addresses themselves do not provide any inherent security features.
9. MAC address collisions: In rare cases, MAC addresses can collide, which can cause network disruptions and make it difficult to identify and manage devices on the network.