The Information Used by a Switch to Forward Ethernet Frames

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A switch is a networking device that operates at the data link layer (layer 2) of the OSI model. It is responsible for forwarding Ethernet frames between devices connected to its ports.

When an Ethernet frame arrives at a switch, it examines the destination MAC address in the frame's header to determine where to forward the frame. The MAC address is a unique identifier assigned to each network interface card (NIC) in a device.

The switch maintains a MAC address table that maps MAC addresses to the switch ports where the devices are connected. When a frame arrives at the switch, it checks the MAC address table to determine if it has a mapping for the destination MAC address. If the MAC address is not found in the table, the switch floods the frame to all ports except the port where the frame was received. This flooding process is used to learn the MAC address and its associated port.

Once the switch determines the destination port for the frame, it forwards the frame only to that port. This process of forwarding frames based on the destination MAC address is known as switching.

To summarize, a switch uses the destination MAC address in an Ethernet frame to forward the frame to its destination. The switch maintains a MAC address table that maps MAC addresses to switch ports to facilitate this forwarding process.