D. The device learns the source MAC addresses from traffic in the network and stores this MAC address in addition to the interface from which the traffic was received. Here’s how this process typically works: When a Junos device is connected to an Ethernet LAN, it listens to the traffic on each of its interfaces. As traffic flows through the device, it observes the source MAC addresses of the frames arriving on each interface. The Junos device then associates each MAC address it observes with the specific interface from which it received the traffic. This information is stored in the Ethernet switching table (also known as MAC address table) of the device. By observing the source MAC addresses in the incoming frames, the device builds its understanding of which MAC addresses are reachable via which interfaces.