Which feature of an L2 switch allows network administrators to segment a…

Concept

A broadcast domain is the set of devices that receive one another's broadcast frames. By default, every port on a single Layer-2 switch belongs to one broadcast domain, so a broadcast sent by any host reaches all hosts on that switch. To split this single domain into several independent logical networks, a switch feature must place groups of ports into separate broadcast domains, so a broadcast in one group is never seen by another group.

Applying it here

A VLAN (Virtual Local Area Network) does exactly this. It logically groups switch ports (independent of their physical location) into distinct broadcast domains. Each VLAN behaves like a separate physical network: broadcasts stay within their own VLAN, and traffic between VLANs requires a Layer-3 device (a router or a Layer-3 switch). One physical switch can therefore host many isolated networks.

Why the others do not fit

• Spanning Tree Protocol (STP) — a loop-prevention mechanism that blocks redundant paths to keep the topology loop-free; it does not partition broadcast domains.

• Port Mirroring — copies traffic from one port to a monitoring port for analysis; it observes traffic rather than segmenting it.

• Link Aggregation — bundles several physical links into one logical link for higher bandwidth and redundancy; the combined link still sits in one broadcast domain.

• QoS (Quality of Service) — prioritises and schedules traffic to manage congestion and latency; it changes how packets are treated, not how the network is divided.

Conclusion

The feature that segments one switch into multiple independent broadcast domains is the VLAN.