“Gratuitous ARP” means different things in different sources. This topic collects the notes on how, with links to where each is discussed
Requests, replies or both. The term is used for both, often without saying which. RFC5944 allows either @ref, while some sources use it for replies alone. RFC5227 named the request an announcement partly for this reason. See GratuitousARPMessages and ARPAnnouncement
Gratuitous request or announcement. The packets are identical; “announcement” signals RFC 5227’s conflict detection procedure. These notes treat ARPAnnouncement as a purpose and GratuitousARPRequest as the packets. Wireshark’s own announcement flag is narrower still: a gratuitous request with Target MAC 00:00:00:00:00:00@ref
Probes called gratuitous. An ARPProbe is sometimes called gratuitous for being unsolicited, though by form it isn’t: its Sender IP is 0.0.0.0
What these notes use.GratuitousARPMessages is defined by form: Sender IP = Target IP, not 0.0.0.0, requests and replies both. See ARPTopicTerms for family, shape and purpose
MIKE HIGGINBOTTOM