What Is a Network Switch?

Imagine an office where everyone shares a single telephone line. When anyone makes a call, everyone else has to wait. When someone receives a call, everyone's phone rings. This was networking before switches—chaos disguised as connectivity.

A network switch solved this by giving each device its own dedicated line. It connects multiple devices within a local network, forwarding data only to the intended recipient rather than broadcasting it to everyone. This simple change transformed networking from a shared shouting match into millions of simultaneous private conversations.

How Switches Work

When you plug your computer into an office network, you're connecting to a switch. The switch learns who's connected where by examining the source MAC address of every frame it receives. It builds a table—called the MAC address table—mapping addresses to physical ports.

When data arrives destined for a specific device, the switch consults its table and forwards the frame only to the correct port. The sender and receiver get dedicated bandwidth between them. Other ports aren't involved. Other conversations continue undisturbed.

This learning process is automatic and continuous. When a switch powers on, its table is empty. As frames arrive, the switch records where each device lives. If a frame arrives for an unknown destination, the switch floods it out all ports except the source—but only until the destination responds and reveals its location. Entries age out after a few minutes of silence, so the switch adapts when devices move or disconnect.

What's Inside a Switch

Ports provide physical connections. Switches range from 5-port home office models to enterprise units with 48 or more ports. Speeds range from 100 Mbps to 100 Gbps, with Gigabit (1000 Mbps) standard for desktop connections.

The MAC address table stores mappings between addresses and ports—typically thousands to hundreds of thousands of entries.

The switching fabric is the internal architecture that moves data between ports. Modern designs (shared memory, crossbar matrices) achieve high throughput and low latency.

Power over Ethernet (PoE) circuitry in equipped switches delivers electrical power over network cables to devices like wireless access points, IP phones, and security cameras—one cable for data and power.

Switch Types

Unmanaged switches just work. Plug in cables, traffic flows. No configuration, no features, no complexity. Perfect for small networks needing basic connectivity.

Managed switches offer configuration through web interfaces, command lines, or management protocols. VLANs, port mirroring, quality of service, monitoring—the tools larger networks need for control and visibility.

Smart switches split the difference: limited configuration through a web interface, some advanced features, lower cost than fully managed.

Layer 2 switches forward based on MAC addresses. This describes most switches.

Layer 3 switches add routing capabilities, making forwarding decisions based on IP addresses while maintaining hardware-speed performance. They blur the line between switch and router.

Core switches provide high-capacity interconnection in large networks, connecting access and distribution switches with 10/40/100 Gbps uplinks.

Key Features

VLANs logically segment one physical network into multiple isolated networks. Devices in different VLANs can't communicate without routing—security and organization on a single switch.

Link aggregation combines multiple physical connections into one logical link. Four 1 Gbps ports become a 4 Gbps connection with built-in redundancy.

Spanning Tree Protocol (STP) prevents switching loops. Without it, redundant connections would cause broadcast storms that crash the network. STP blocks certain ports to maintain a loop-free topology while keeping backup paths ready.

Quality of Service (QoS) prioritizes traffic. Voice calls don't stutter because someone's downloading a large file.

Port mirroring copies traffic from one port to another for monitoring—security analysis, performance troubleshooting, debugging.

IGMP snooping optimizes multicast by forwarding it only to ports with interested receivers, not flooding everywhere.

Performance

Switching capacity is the total traffic the switch can handle, measured in Gbps or Tbps. A 48-port Gigabit switch might have 96 Gbps capacity (48 ports × 1 Gbps × 2 for full-duplex).

Forwarding rate measures packets per second. Small packets create more processing work than large packets at the same bandwidth.

Latency is the delay introduced while processing frames—typically microseconds. Lower is better.

Buffer size determines how much data the switch can store during congestion. Larger buffers prevent packet loss during bursts but can increase latency.

A "wire-speed" switch handles full line rate on all ports simultaneously without drops—the performance target.

Switches vs. Hubs

A hub is a party where everyone has to stop talking whenever anyone speaks. A switch is a party where every pair of people gets their own private room.

Hubs repeat all received traffic out all other ports. Device A sends to device B; devices C, D, and E all receive it anyway. Everyone shares one collision domain. Only one device can transmit at a time.

Switches forward traffic only to the intended port. A talks to B while C talks to D—simultaneously, no interference. Each port is its own collision domain. Full-duplex means sending and receiving at the same time.

Hubs are essentially extinct—so obsolete that they're actually difficult to buy. Switches became cheap enough that hubs have no remaining purpose.

Switches vs. Routers

Switches operate at Layer 2, forwarding based on MAC addresses within a single network. They connect devices in the same broadcast domain.

Routers operate at Layer 3, forwarding based on IP addresses between different networks. They separate broadcast domains and make routing decisions about the best path.

Layer 3 switches perform routing in hardware at switch speeds, though they typically lack some advanced routing features.

Most networks use both: switches connect devices within locations, routers connect locations together and provide Internet access.

Scaling Up

Switch stacking connects multiple physical switches into one logical unit with shared configuration and MAC tables. Special stacking cables provide 40-480 Gbps between units.

Chassis-based switches use modular designs where line cards plug into a central chassis. Hundreds of ports, very high performance, significant cost.

Cloud-managed switches centralize management through web services, simplifying multi-site deployments.

Troubleshooting

Managed switches reveal what's happening:

Port statistics show connection status, speed, duplex settings, error counts. Excessive errors suggest bad cables or faulty interfaces.

MAC address table shows which devices connect where. Can't reach something? Check if the switch knows about it.

VLAN configuration causes many connectivity problems. Wrong VLAN assignments or misconfigured trunk ports break communication.

Link lights provide quick visual status—green for good connections, amber for problems.