What is Gratuitous ARP?

What is Gratuitous ARP?

• A. Send ARP requests to broadcast with sender and target address the same (sender's address)
• B. Respond to ARP requests with its own address
• C. Broadcast its IP/MAC pairing to segment
• D. Request broadcast to refresh ARP table periodically

Answer: (A)

Gratuitous ARP is an ARP request sent to all devices on the local network to announce the sender’s own IP-to-MAC mapping. The key is that the request uses the sender’s IP as both the source and the target, and it’s broadcast so every host on the segment hears it. This unsolicited broadcast updates neighbors’ ARP caches with the new mapping and helps detect IP address conflicts, since another device using the same IP would respond and reveal the clash. That’s why the best description is the one that says it sends ARP requests to broadcast with the sender’s address as both the sender and the target. The other options describe ARP replies or general broadcasting of a mapping or periodic refresh—behaviors that don’t capture the specific unsolicited, self-addressed ARP announcement meant by gratuitous ARP.

Gratuitous ARP is an ARP request sent to all devices on the local network to announce the sender’s own IP-to-MAC mapping. The key is that the request uses the sender’s IP as both the source and the target, and it’s broadcast so every host on the segment hears it. This unsolicited broadcast updates neighbors’ ARP caches with the new mapping and helps detect IP address conflicts, since another device using the same IP would respond and reveal the clash. That’s why the best description is the one that says it sends ARP requests to broadcast with the sender’s address as both the sender and the target. The other options describe ARP replies or general broadcasting of a mapping or periodic refresh—behaviors that don’t capture the specific unsolicited, self-addressed ARP announcement meant by gratuitous ARP.