Means: “I have this IP.” Sent after a successful ARPProbe as part of ARPDuplicateAddressDetection, after an IP change or failover, and by some devices as a keepalive. @ref
An ARP Announcement is a GratuitousARPRequest; the difference is in terminology and context. It’s just a specific use case. @ref
Because it’s a request, a device that already owns that IP may reply. That’s how it can reveal an IP conflict during ARPDuplicateAddressDetection.
Ethernet src not matching Sender MAC: another card sent the frame on the ARP sender’s behalf, as with a bridged or virtualised host, ProxyARP or MACAddressSpoofing
MIKE HIGGINBOTTOM