What is the function of a switch in a network?

A switch in a network is a device that operates at the data link layer (Layer 2) of the OSI (Open Systems Interconnection) model. Its primary function is to forward data frames within a local area network (LAN). Switches are commonly used to connect multiple devices, such as computers, printers, and other networking devices, within a specific network.

Here's a more detailed technical explanation of the functions of a switch:

  1. MAC Address Learning:
    • Switches use Media Access Control (MAC) addresses to uniquely identify devices on a network. When a switch receives a frame, it examines the source MAC address in the frame header.
    • If the source MAC address is not already in the switch's MAC address table (also known as a forwarding table or content addressable memory - CAM table), the switch adds an entry mapping the source MAC address to the port through which the frame was received.
  2. Forwarding:
    • Once the switch has learned the MAC addresses and their corresponding ports, it can make forwarding decisions. When a frame arrives at a switch, the switch looks up the destination MAC address in its MAC address table.
    • If the destination MAC address is found in the table, the switch forwards the frame only to the port associated with that address, preventing unnecessary traffic on other ports.
  3. Filtering and Flooding:
    • If the destination MAC address is not in the table, the switch employs a strategy known as flooding. It sends the frame out to all ports (except the incoming port), allowing the destination device to receive the frame and update its MAC address table.
    • Once the destination device responds, the switch learns the corresponding MAC address and updates its table accordingly.
  4. Loop Avoidance:
    • Switches also implement loop avoidance mechanisms, such as the Spanning Tree Protocol (STP). STP helps identify and block redundant paths in the network, preventing loops that could lead to broadcast storms and network instability.
  5. VLAN Support:
    • Switches often support Virtual LANs (VLANs), which allow the network to be logically segmented. VLANs enable the creation of multiple broadcast domains within a single physical network, improving network performance and security.
  6. Quality of Service (QoS):
    • Some advanced switches support Quality of Service features, allowing for the prioritization of certain types of traffic. This ensures that time-sensitive data, such as voice or video, is given higher priority for faster delivery.