This puzzle shows you what happens when there are duplicate MAC addresses. This rarely happens, but it used to happen more often than should be statistically probable. Cheap network card vendors used to make batches of cards with the same MAC address, and occasionally someone would buy two of them. The best solution is to replace one of the NICs that has the duplicate MAC address. Ping both pc0 and pc1 from pc2. Duplicate MAC addresses 1024 1024 100 True 1 7 132 full net_switch0 100 100 430,270 net_switch False False 0.0.0.0 0.0.0.0 0.0.0.0 gw lo lo0 100 101 net_switch0 lo0 lo 101 False lo0 127.0.0.1 255.0.0.0 0.0.0.0 ip management_interface management_interface0 100 102 net_switch0 management_interface0 management_interface 102 False management_interface0 0.0.0.0 0.0.0.0 0.0.0.0 ip port port1 100 103 net_switch0 port1 port 103 False port1 0.0.0.0 0.0.0.0 0.0.0.0 ip port port2 100 104 net_switch0 port2 port 104 False port2 0.0.0.0 0.0.0.0 0.0.0.0 ip port port3 100 105 net_switch0 port3 port 105 False port3 0.0.0.0 0.0.0.0 0.0.0.0 ip port port4 100 106 net_switch0 port4 port 106 False port4 0.0.0.0 0.0.0.0 0.0.0.0 ip port port5 100 107 net_switch0 port5 port 107 False port5 0.0.0.0 0.0.0.0 0.0.0.0 ip port port6 100 108 net_switch0 port6 port 108 False port6 0.0.0.0 0.0.0.0 0.0.0.0 ip port port7 100 109 net_switch0 port7 port 109 False port7 0.0.0.0 0.0.0.0 0.0.0.0 ip pc0 100 120 150,450 pc False False 0.0.0.0 0.0.0.0 0.0.0.0 gw lo lo0 120 121 pc0 lo0 lo 121 False lo0 127.0.0.1 255.0.0.0 0.0.0.0 ip eth eth0 120 122 pc0 eth0 eth 122 False eth0 192.168.1.1 255.255.255.0 0.0.0.0 ip pc1 100 123 420,560 pc False False 0.0.0.0 0.0.0.0 0.0.0.0 gw lo lo0 123 124 pc1 lo0 lo 124 False lo0 127.0.0.1 255.0.0.0 0.0.0.0 ip eth eth0 123 125 pc1 eth0 eth 125 False eth0 192.168.1.2 255.255.255.0 0.0.0.0 ip pc2 100 126 740,450 pc False False 0.0.0.0 0.0.0.0 0.0.0.0 gw lo lo0 126 127 pc2 lo0 lo 127 False lo0 127.0.0.1 255.0.0.0 0.0.0.0 ip eth eth0 126 128 pc2 eth0 eth 128 False eth0 192.168.1.3 255.255.255.0 0.0.0.0 ip 120 122 pc0 eth0 100 103 net_switch0 port1 normal 129 123 125 pc1 eth0 100 104 net_switch0 port2 normal 130 126 128 pc2 eth0 100 105 net_switch0 port3 normal 131 pc2 pc0 SuccessfullyPings pc2 pc1 SuccessfullyPings MACAddress