Here's a simple program that spoofs an ARP reply for a given IP address. If I spin up two terminal sessions on the same machine. Run this code in one window % ./spoof en0 192.168.1.7 Listening on en0 for ARP requests to 192.168.1.7 Spoofing MAC: 00:0c:87:47:50:27 And in the second window cause the OS to issue an ARP_REQ % ping 192.168.1.7 You will see the program respond to the ARP request. (Wireshark will see the ARP_REQ and ARP_REPLY packets) however my arp table isn't updated with the MAC for the IP address. There is no firewall active. % arp -a|grep 192.168.1.7 (192.168.1.7) at (incomplete) on en0 ifscope [ethernet] This is running on a MacBook pro M3 (OSX 15.4). HOWEVER, on a MacBook pro M4 (OSX 15.2) is does Work !!!!! Can anyone explain why its not working? spoof.txt