i am a graduate in computer science and have  keen interest in the linux operating system.presently i am implementing a firewall developed with VJ as a front end and C on the backend.The back end is totally implemented on linuxOS.This involved indepth knowledge of the PacketFiltering capabilities of Linux.So while doing this i came to know about many interesting aspects of Linux Kernel Internals and of Networking in Linux.I tried to implement many of these things and got success in some of them.I have changed the packet filtering code os the linux kernel to meet our specific requirements.Also wrote two-three system calls to implement the customized firewall with Novell Netware being the front end user and Linux Server being the gateway for all the traffic.