How to capture a sequential stream of data between two machines, making no assumptions about network layer protocols? On wired network, one can do it by ARP spoofing and then sniff the network. One wireless network, could it be possible? Or could one disguise its MAC and receiving data from both S and D at the same time?
In addition, some WiFi has password on it, and some doesn't. It is said that using a WiFi that doesn't have a password is significantly insecure. Why? How could others attack or monitor my activities with a network without password?
One more question. It is said that facilities like airpcap can be used to do such things like monitoring the WiFi network. What is its principles? Could I achieve similar goals without such kind of facilities? (PS: airpcap is fairly not cheap :/ )