Which action constitutes NDP Gratuitous ARP?

• A. Spoofing bogus address in the NA response
• B. Spoofing non-existent addresses in NS requests
• C. Spoofing address in the NS request
• D. Spoofing a Router Advertisement (RA) to redirect traffic

Answer: (C)

Gratuitous Neighbor Discovery uses an unsolicited Neighbor Solicitation to announce an IPv6 address and map it to the sender’s MAC on the local link. In this scenario, that means crafting the NS so that the Target Address is the address you want others to associate with you (essentially spoofing the address in the NS request). By doing this, neighboring devices learn or refresh their caches with the correct IPv6-to-MAC mapping and can also detect duplicates for that address.

Other ND actions described would serve different purposes: responding with a Neighbor Advertisement is part of the normal reply path, soliciting non-existent addresses isn’t how gratuitous announcements work, and spoofing a Router Advertisement aims to redirect traffic rather than update address mappings.