Which device operates at both Layer 2 and Layer 3?

Correct answer: Layer 3 switch

Option B is correct because a Layer 3 switch combines traditional Layer 2 switching (MAC address-based forwarding) with Layer 3 routing (IP address-based forwarding) in a single hardware device, allowing it to operate at both OSI layers simultaneously. Option A, a bridge, operates only at Layer 2, forwarding frames based on MAC addresses between network segments. Option C, a repeater, operates at Layer 1, simply amplifying or regenerating electrical signals without any address awareness. Option D, a hub, also operates at Layer 1, broadcasting all incoming signals to every port without any intelligence at Layer 2 or above.