It's called Mac Spoofing. Most Piso Wifi doesn't have counter for this kind of phishing attack...
for some Piso Wifi that does not use IP and MAC as authentication is a hassle for the customer.
it works like this...
Server: Are you 10.0.0.5?
10.0.0.5: Yes
Server checks if the MAC ADDRESS is correctly associated with the IP
The PenTester: ARP scans the network for suitable target. and see's 10.0.0.5
The PenTester: Copies Both IP and MAC of the Target and disguises at 10.0.0.5.
Of course the server/router will be confused because there are 2 10.0.0.5. What the server does to avoid erring out is to treat the new device which is The PenTester as the same as 10.0.0.5 user.
basically accessing the 10.0.0.5 and kicking the target out of the network(For some Servers/Routers the Victims Perspective are still connected but does not receive and packets/data).