What are MAC addresses?
MAC addresses are physical addresses that are associated with network device interfaces. They consist of a 48-bit combination of numbers and are unique to each network device. MAC addresses enable the identification and communication of network devices in Ethernet networks. Each network card has a unique MAC address, with the first half (3 bytes or 24 bits) identifying the manufacturer.
What are MAC addresses used for?
When network devices in a local network send messages to each other, they add the sender's MAC address and the receiver's MAC address to the data packet. When the data packet arrives at the receiving device's network interface, the device checks the receiver's MAC address. If the receiver's MAC address matches the device's own MAC address, the data packet is accepted and received. Otherwise, the data packet is rejected.
Network Listening
It is important to note that if a packet arrives at your network card that is intended for a different MAC address than the one burned into the network card, the packet will still be processed by your computer's network stack, which means that you can see the packet, for example, in the Wireshark tool that can monitor your computer's network traffic.
MAC Address Spoofing
Another important point is that even though the network interface card comes with a unique MAC address, its usage is completely voluntary. The computer is free to decide which MAC address it assigns to itself or even send a different MAC address in each packet.
Test your knowledge
How does the network machine process a data packet whose recipient's MAC address does not match its own MAC address?
Can MAC addresses be trusted in data network access control?
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