If a host acquires and puts to use an IP address that happens to already be in use on the network, it will cause connectivity issues for both hosts @ref
A host can check if an IP is in use by sending a few ARP Probes which can’t pollute anyone’s cache (typically 3)
If no one responds, the host will consider this IP address unique and officially claim the IP address with two ARPAnnouncement a couple of seconds apart. @ref
If the IP address in question is already in use, the initiator of the ARP Probe will expect an ARPAnnouncement from the original owner @ref
The initiator’s reaction to finding the IP in use would be different depending upon how it acquired the IP address. If it acquired the IP address using DHCP, it might try to ask for a new (unused) IP address from the DHCP server. If it acquired the IP address statically, then it simply doesn’t use the IP address and waits for the administrator to reconfigure a new IP address. @ref
Only difference between in the data in an ARPAnnouncement and in an ARPProbe is the ARP Sender IP is filled in for an announcement so the ARPCache can be updated due to there being a complete MAC/IP mapping @ref
Not all devices perform duplicate address detection @ref
MIKE HIGGINBOTTOM