tcp dump enables us to capture the packets over a network. But there might be a problem when you run this on localhost. Like you are running a socket program, and both server and client residdes in localhost only, then it will not work. The reason for it is: " It's not reaching the Network Card (NIC) actually when it's in localhost." This problem has not been reported anywhere. So, always try this thing on two different machines, may be in a LAN. B'coz the request will never reach the card and will not filter request for a particular port.
The blog will contain all the Technical knowledge I have to share and I welcome & would appreciate others for sharing their knowledge :0)