Dear L7Sqr, With regards to the thread what exactly should be changed to avoid any future problem. So I am not used to using thread in C either. Yes as for my question with regards to tcpdump. I have now managed to solve to find the ether_type. So now for e.g. if the ether_type is TCP so I should explore the print-ip.c codes right? So I am now exploring it and stuck on which one of the function should be called first?