There are several methods to do this, but the one I describe here is MAC Spoofing method. All I say here is only a brief idea on how to hack your own home or small office network. Anyhow this is even applicable for large networks but intrusion detection or prevention systems could be handled in large networks for such spoofing attacks.
This is not a step by step procedure but I would help you if you have any issues. Okay! Say you have a small network of 3 peoples (Tony, Mark & Shane) sharing a single Internet Connection. All three computers are connected to a switch (not hub) and then to a Modem or Router. Switch keeps maintaining a MAC Address Table of IP address to MAC address entries.
This must be the setup of almost any small office networks. Now, Shane wants to monitor the traffic of two of his other staff, Tony and Mark. He doesn’t want to harm them but he just wants a passive way of monitoring the traffic of Tony and Mark. He chosen the method called “MAC Address Spoofing”. A brief description of what is MAC Spoofing –
“MAC Address Spoofing is replacing true MAC Address with a different MAC address to hide the identity of the equipment. Every network interface will have a unique address called MAC address. This is unique 48 bit number and assigned at the time of manufacturing. No other network interface will have same MAC address. So during attacks, it is safe to replace MAC address.”
Shane understood the concept of MAC Address Spoofing clearly and he downloaded a tool (SMAC MAC Address Changer) to change his computer’s MAC address (11:22:3F:7E:F1:25) to the MAC Address of the Modem/Router (01:1B:22:FF:25:01). After few seconds, Switch updates its MAC Table as
As you see, Switch MAC Table is updated with Router’s MAC address for both Shane computer (10.1.1.3) and the Router (10.1.1.254). Now when Tony tries to connect to Internet, Switch receives the data packet and looks into its MAC Table. Then it forwards the data packet to both Router and Shane Computer. Shane then uses WireShark tool to sniff all the traffic that is coming to his network card including that of Tony. Though Shane could miss out some of the inside traffic but all traffic destinated to router would reach his computer also.