Which device operates at OSI Layer 2?

A switch operates primarily at OSI Layer 2, the Data Link layer. It forwards Ethernet frames based on MAC addresses and builds a MAC address table to determine which port should receive traffic. This makes switching more efficient than a hub, which operates at Layer 1 and repeats signals without understanding frames. A router operates at Layer 3 by forwarding packets based on IP addresses and routing tables. A modem is generally associated with physical or access-layer signal conversion rather than Layer 2 switching. Layer 2 switching is important for local network communication, VLAN segmentation, and broadcast domain control. Security teams need to understand Layer 2 because attacks such as MAC flooding, VLAN hopping, and ARP spoofing can occur at this level. While switches are not the same as firewalls, proper switch configuration supports network segmentation and reduces unnecessary traffic exposure. Reference/topics: Network Fundamentals 2.7, devices operating Layers 1 through 4; Network Security 3.1, VLANs.