Editing Address Resolution Protocol (section)

==ARP probe==
An '''ARP probe''' in IPv4 is an ARP request constructed with the SHA of the probing host, an SPA of all 0s, a THA of all 0s, and a TPA set to the IPv4 address being probed for.  If some host on the network regards the IPv4 address (in the TPA) as its own, it will reply to the probe (via the SHA of the probing host) thus informing the probing host of the address conflict.  If instead there is no host which regards the IPv4 address as its own, then there will be no reply.  When several such probes have been sent, with slight delays, and none receive replies, it can reasonably be expected that no conflict exists.  As the original probe packet contains neither a valid SHA/SPA nor a valid THA/TPA pair, there is no risk of any host using the packet to update its cache with problematic data.  Before beginning to use an IPv4 address (whether received from manual configuration, DHCP, or some other means), a host implementing this specification must test to see if the address is already in use, by broadcasting ARP probe packets.{{Ref RFC|5227}}<ref>{{cite web |last1=Harmoush |first1=Ed |title=ARP Probe and ARP Announcement |url=https://www.practicalnetworking.net/series/arp/arp-probe-arp-announcement |website=Practical Networking |publisher=PracticalNetworking .net |access-date=3 August 2022}}</ref>