A network switch connects devices (such as computers, printers, wireless access points) in a network to each other, and allows them to ‘talk’ by exchanging data packets. Switches can be hardware devices that manage physical networks, as well as software-based virtual devices.
Switches form the vast majority of network devices in modern data networks. They provide the wired connections to desktop computers, wireless access points, industrial machinery and some internet of things (IoT) devices such as card entry systems. They connect the computers that host virtual machines (VMs) in data centers, as well as the physical servers, and much of the storage infrastructure. They carry vast amounts of traffic in telecommunications provider networks.
A network switch operates on the network layer 2 of the OSI model. In a local area network (LAN) using Ethernet, a network switch determines where to send each incoming message frame by looking at the physical device address (or MAC address). Switches maintain tables that match each MAC address, to the port which the MAC address is received.
How a network switch works
A network switch can be deployed in the following ways:
- Edge, or access switches: These switches manage traffic either coming into or exiting the network. Devices like computers and access points connect to edge switches.
- Aggregation, or distribution switches: These switches are placed within an optional middle layer. Edge switches connect into these and they can send traffic from switch to switch or send it up to core switches.
- Core switches: These network switches form the backbone of the network. Core switches connect either aggregation or edge switches, user or device edge networks to data center networks and enterprise LANs to routers.
If a frame is forwarded to a MAC address unknown to the switch infrastructure, it is flooded to all ports in the switching domain. Broadcast and multicast frames are also flooded. This is known as BUM flooding -- broadcast, unknown unicast, and multicast flooding. This capability makes a switch a Layer 2 or data-link layer device in the Open Systems Interconnection (OSI) communications model.