Building a Linux firewall

has anyone out there got a complete working code on linux based firewall?? plz help!!

hey ,
we r doing project on a network security.. we r going to build a DMZ for a private network. In which we r supposed to build our own firewall on linux. so could u plz guide us regarding how to start with the project.. we would be very thankful to u if u provide us with the complete soursecode ..my id is rati_flyhigh@rediffmail.com

i'm building a linux firewall in bash en a configuration file can somebody help me with a complete code so i can have an idea how i can began,my e-mail is mgend_@hotmail.com

# cat set_policy.c

#include <stdio.h>

#include <string.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <linux/ip.h>

#include <linux/tcp.h>

#include <linux/udp.h>

#include <linux/ip_fw.h>

main(int argc, char **argv)

{

int p, sfd;

struct ip_fw fw;

fw.fw_flg = 0;

if (strcmp(argv[1], "accept") == 0) {

p = IP_FW_F_ACCEPT;

}

else if (strcmp(argv[1], "reject") == 0) {

p = IP_FW_F_ICMPRPL;

}

else if (strcmp(argv[1], "deny") == 0) {

p = 0;

}

sfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

setsockopt(sfd, IPPROTO_IP, IP_FW_POLICY_FWD,

&p, sizeof(int));

}