LAN Switching Functions and Frame Forwarding

Main Functions of a LAN Switch

• Connect multiple devices within a Local Area Network (LAN) to facilitate communication.
• Operate at the Data Link Layer (Layer 2) of the OSI model, making decisions based on MAC addresses.
• Improve network efficiency and speed by reducing collisions and creating a dedicated communication path.

Forwarding a Known Unicast Frame

• When a switch receives a known unicast frame, it checks its MAC address table for the corresponding MAC address.
• If the MAC address is found, the switch forwards the frame only to the specific port connected to that address.
• This process minimizes unnecessary traffic across the network.

Forwarding a Known Frame to a Second Switch

• If a switch needs to forward a known frame to another switch, it follows similar logic by looking up the destination MAC address.
• The frame is sent out through the appropriate trunk link connecting the two switches.
• Proper VLAN tagging is crucial to maintain data separation across different networks.

Learning MAC Addresses

• A switch learns MAC addresses by examining the source MAC address of incoming frames.
• The address is then added to the MAC address table along with the port number from which the frame was received.
• This learning process helps to build an efficient switching table for future frame forwarding.

Switch Forwarding Logic Summary

• The switch uses a MAC address table to map devices to their respective ports.
• When a frame is received, the switch checks if the MAC address is in the table.
• If the address is known, the frame is forwarded to the designated port; if unknown, it is broadcast to all ports except the incoming port.

"show mac address-table dynamic" Command

• This command displays the dynamically learned MAC addresses stored in the switch's MAC address table.
• It provides information on the MAC addresses, associated ports, and the VLANs they belong to.
• Useful for troubleshooting and verifying correct operation of the switch.

This quiz covers the main functions of a LAN switch including its role in connecting devices within a Local Area Network and how it operates at the Data Link Layer. It also explains the process of forwarding known unicast frames and the importance of VLAN tagging when communicating between switches.