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Layer2 switches learn MAC addresses automatically, building a table which can be used to selectively forward packets.
Intelligent packet forwarding (routing) based on Layer3 information is traditionally the function of routers
Layer2 Switches (The Data-Link Layer)
Layer2 switches operate using physical network addresses. Physical addresses, also known as link-layer, hardware, or MAC-layer addresses, identify individual devices. Most hardware devices are permanently assigned this number during the manufacturing process.
Switches operating at Layer2 are very fast because they’re just sorting physical addresses, but they usually aren’t very smart—that is, they don’t look at the data packet very closely to learn anything more about where it’s headed.
Layer3 Switches (The Network Layer)
Layer3 switches use network or IP addresses that identify locations on the network. They read network addresses more closely than Layer2 switches—they identify network locations as well as the physical device. A location can be a LAN workstation, a location in a computer’s memory, or even a different packet of data traveling through a network.
Switches operating at Layer3 are smarter than Layer2 devices and incorporate routing functions to actively calculate the best way to send a packet to its destination. But although they’re smarter, they may not be as fast if their algorithms, fabric, and processor don’t support high speeds
