MAC Addresses Explained
1. What is a MAC Address?
A MAC (Media Access Control) address is a unique identifier assigned to network interfaces for communications at the data link layer of a network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and Wi-Fi. A MAC address is typically represented as six groups of two hexadecimal digits, separated by colons or hyphens, such as 00:1A:2B:3C:4D:5E.
2. Structure of a MAC Address
A MAC address consists of 48 bits, divided into two parts: the Organizationally Unique Identifier (OUI) and the Network Interface Controller (NIC) specific address. The first 24 bits (three octets) represent the OUI, which is assigned by the IEEE to manufacturers. The remaining 24 bits are assigned by the manufacturer to uniquely identify each network interface.
Example: In the MAC address 00:1A:2B:3C:4D:5E, the OUI is 00:1A:2B, and the NIC specific address is 3C:4D:5E. The OUI 00:1A:2B might be assigned to a specific manufacturer, such as Cisco, while the NIC specific address 3C:4D:5E is unique to a particular network interface card produced by that manufacturer.
3. Role of MAC Addresses in Networking
MAC addresses play a crucial role in local network communication. When a device wants to communicate with another device on the same local network, it uses the destination device's MAC address. The MAC address is used at the data link layer to ensure that data frames are delivered to the correct device. Routers and switches use MAC addresses to forward data packets to the appropriate destination within a local network.
Example: When a computer on a local network wants to send data to another computer, it first checks the destination IP address. If the destination is on the same local network, the computer uses ARP (Address Resolution Protocol) to find the MAC address of the destination device. The data is then encapsulated in a frame with the destination MAC address and sent over the network.
4. MAC Address Spoofing
MAC address spoofing is the act of changing the MAC address of a network interface to impersonate another device. This can be done for various reasons, such as bypassing network access controls or hiding the identity of a device. However, MAC address spoofing can also be used maliciously to perform network attacks.
Example: Suppose a network administrator has implemented MAC address filtering to restrict access to the network. A user might spoof their MAC address to match one of the allowed addresses, thereby gaining unauthorized access to the network. This is why relying solely on MAC address filtering for security is not recommended.