On a LAN, it's not uncommon to see a gratuitous ARP, which is an unsolicited ARP used to prevent duplicate IP addresses on a network, which can cause conflicts. To see an example, go to https://www.cloudshark.org/captures/54af88021aa8, and then download and open the file in Wireshark. Or, you can view the details in CloudShark.

In this example, we see a gratuitous ARP where the source and destination IP addresses are both set to the IP of the sending machine. As shown in the following screenshot, you can see Sender IP address: 192.168.130.128, which is the same as Target IP address: 192.168.130.128:

As shown, a gratuitous ARP request is sent as a broadcast; however, no reply is expected. This type of ARP is a way for a host to share IP and MAC address pairings so that all hosts on the network can update their ARP tables.

Next, we'll see an example that is not actually an ARP type, but a technique used on the network called a proxy ARP.