A network switch is a core device used in computer networks to interconnect multiple network devices together. Switches operate at layer 2 (data link layer) of the OSI model and use MAC addresses to forward data packets between different segments of a network. Understanding how a switch works provides key insights into local area network (LAN) operations.
At its core, a switch provides a hardware-based bridging function. When a switch receives a data frame on one of its ports, it examines the destination MAC address in that frame and checks its MAC address table to determine which port should receive the frame. The switch then forwards the frame out the appropriate port. If the destination MAC address is not in the table, the switch floods the frame out all ports (except the receiving port).
Switches build their MAC address tables by examining the source MAC address of each frame received. The source MAC is associated with the port on which the frame arrived. By learning MAC locations, switches build dynamically updated address tables. This provides an advantage over older network hubs which simply replicated frames to all connected nodes.
An important element in a switch's operation is the use of application-specific integrated circuits (ASICs). ASICs enable very fast packet forwarding by handling compute-intensive tasks in dedicated hardware. Packet buffers are used to temporarily store frames during times of congestion. High-speed switches often include multiple ASICs and large packet buffers for maximum throughput.
Switches may support multiple interfaces including twisted-pair copper (RJ45), fiber optic, and wireless. Standards-based protocols are used for inter-switch trunking, like 802.1Q VLAN tagging. Switching fabrics connect the different interfaces using shared data buses, matrix configurations, or other internal switching mechanisms.
VLAN support: Traffic is segmented into virtual LANs to logically separate users and resources. Access control lists can restrict connectivity.
Trunking and link aggregation: Multiple interfaces can be bundled together to increase bandwidth between switches.
Spanning tree protocol: Loop prevention is used to disable redundant paths in meshed networks.
Quality of service (QoS): Traffic prioritization techniques reserve bandwidth for critical applications.
Port monitoring/mirroring: Dedicated monitoring ports can copy traffic for analysis.
Switches may also provide features for network management and security, like SNMP monitoring, authentication, and encryption. By integrating many key functions, a network switch is indispensable for building scalable and efficient LANs. Understanding how switches forward frames, learn MAC addresses, and handle congestion provides critical insights for troubleshooting and optimizing modern computer networks.