JNCIS-SP: Juniper Networks Certified Specialist – Service Provider Routing (2023) — Question 58

How does a Junos device learn about MAC addresses when it is first connected to an Ethernet LAN?

Answer options

• A. The device sends out a network multicast message asking for all devices and MAC addresses on the network and stores this information in addition to the interface from which the response was received.
• B. The device sends out a network broadcast message asking for all devices and MAC addresses on the network and stores this information in addition to the interface from which the response was received.
• C. The device learns the destination MAC addresses from traffic in the network and stores this MAC address in addition to the interface from which the traffic was received.
• 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.

Correct answer: D

Explanation

The correct answer is D because a Junos device learns MAC addresses by examining the source MAC addresses of incoming frames and records them along with the corresponding interface. Options A and B incorrectly describe the type of message used, while option C refers to destination MAC addresses instead of source MAC addresses, which is not how the learning process occurs.