One of the most annoying problems in IP networks is duplicate IP addresses. The funny thing is that if you are familiar with the problem, what causes it, and how to find it, it becomes one of the most simple ones to solve.
When you suspect a duplicate address in the network, the first thing to do will be to use the simple CLI commands—ARP and Ping. If you don't locate the problem, connect Wireshark to the switch and in a large network to every VLAN in the network and move step-by-step until you find the problem.
We start with the phenomena, such as slow access to a server or to another device, slow access to the Internet, and all the pings that you don't get replies to.