What do switches break up?

• A. Collision domains
• B. IP subnets
• C. Broadcast domains
• D. VLAN IDs

Answer: (A)

In Ethernet networks, collisions occur when two devices transmit at the same time on the same shared medium. A switch gives each port its own collision domain, so devices connected to different ports don’t contend with each other on the same segment. This confines any potential collision to only the devices on a single port’s link, preventing it from spreading across the whole network. If you’re using full duplex links, you effectively remove collisions on each point-to-point connection, but the idea remains: each switch port creates a separate collision domain, which is why switches break up collision domains.

IP subnets are a layer 3 concept and are typically broken up by routers (or by VLANs at Layer 2, which can segment broadcast domains but not inherently collision domains). Broadcast domains are the same across a basic switch unless VLANs are used to segment them, while VLAN IDs are a mechanism to partition traffic at Layer 2 to create separate broadcast domains, not to divide collision domains by themselves. The key takeaway is that the primary function of a switch in terms of collision handling is to break up collision domains.