Wednesday, December 16, 2020

What Is Layer 2 in the OSI Model?

To gain an appreciation of the characteristics of addressing, it is helpful to bring forward an example that may be familiar and easy to understand.

Let’s think about this in terms of a mobile home community. Each of the mobile homes have a serial number permanently attached to the home’s frame. Computers have a similar address, called its media access control (MAC) address. That address is “burnt” on to the computers network interface card and is unique in nature. An example of the MAC address is shown in figure 1 below.

MAC (or physical) addressing provides an effective method of moving data across a small community of computing devices where routing traffic between multiple communities is not required. Traffic distribution for these small networks is handled by layer 2 switches that learn the MAC addresses of the computers connected to ports on the switch. The switches then send packets from the sending computer directly to the receiving device. This method of directing traffic helps reduce potential network congestion.

A MAC address consists of a series of 12 hexadecimal numbers. The first six numbers are useful in identifying the manufacturer of the network interface card. The last six numbers are assigned by the card manufacturer, providing a unique addressing scheme. This avoids the possibility of having two computers on the same network with the same physical address.

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