Cisco Certified Network Professional 2025 – 400 Free Practice Questions to Pass the Exam

The role of "src-mac" during an ARP reply validation is to compare with the sender's MAC address. When a device receives an ARP reply, it checks that the source MAC address of the reply matches the MAC address of the sender from whom it initiated the ARP request. This comparison ensures that the response is coming from the device that was expected to respond, maintaining the integrity of the ARP process. By verifying this relationship, the device can prevent possible spoofing attacks and ensure it has the correct MAC address for the intended IP address, thus facilitating accurate packet delivery within the network.

In contrast, validating the target device's MAC or matching the header destination MAC pertains to different aspects of ARP operations rather than the verification of the reply sender. Checking against ARP request contents might also involve additional data, but the core verification focuses on this critical comparison with the sender's MAC address to ensure reliable communication.