Why Do We Use MAC Addresses If IP Addresses Are Unique?

IP addresses and MAC addresses both play critical roles in network communication but serve different purposes at different layers. This article explores the reasons behind the use of MAC addresses, alongside IP addresses, and explains how they work together to facilitate efficient communication in a network.

Key Differences and Purposes

Layer of Operation

The OSI model divides network communication into layers, and MAC and IP addresses operate at different levels. Let's delve deeper into their individual roles and purposes.

MAC Address

Layer 2 - Data Link Layer

MAC addresses are used for local network communication. These hardware addresses are assigned to network interface cards (NICs) and are unique within a network segment. They are essential for close-range communication, such as how devices on the same local network segment can directly send data to each other.

IP Address

Layer 3 - Network Layer

IP addresses, on the other hand, operate at the network layer. They are used to identify devices across different networks and facilitate routing of packets between them. Unlike MAC addresses, IP addresses can be changed, depending on the network a device is connected to, and they are routable over the internet or different networks.

Purpose and Role

Packet Forwarding

When devices within the same local network segment communicate, they use MAC addresses to ensure data is delivered to the correct recipient. However, when packets need to be routed between different networks, routers use IP addresses to determine the best path for the data. Routers don't need to know the MAC addresses of devices in other networks; they only need the destination IP address to forward packets correctly.

Broadcast and Local Communication

MAC addresses are also instrumental in broadcasting messages within a local network. For instance, when a device needs to find the MAC address of another device, it uses a protocol like ARP (Address Resolution Protocol) to send a broadcast message to all devices on the local network. This allows devices to dynamically discover MAC addresses and establish direct communication.

Conclusion

The use of both MAC and IP addresses in network communication ensures efficiency and flexibility. This layered approach, where MAC addresses enable local communication and IP addresses facilitate communication across different networks, provides a robust and scalable network design. The combination of these two address types ensures that data can be routed effectively and that devices can communicate efficiently within and between networks.