Code

/*
 *  T.c
 *
 *  compile: gcc -Wall T2.c -o T2 -lipq
 */

#include <netinet/in.h>
#include <libipq.h>
#include <linux/netfilter.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>

#define BUFSIZE 131072

static void die(struct ipq_handle *h) {

    ipq_perror("passer");
    ipq_destroy_handle(h);

}


void start_packet_engine() {

        int status;
    unsigned char buf[BUFSIZE];
    struct ipq_handle *h;


    printf("\nLaukiame paketu\n");


    h = ipq_create_handle(0, PF_INET);

    if (!h)
        die(h);


    status = ipq_set_mode(h, IPQ_COPY_PACKET, BUFSIZE);

    if (status < 0)
        die(h);


    do {
        status = ipq_read(h, buf, BUFSIZE, 0);
        if (status < 0)
            die(h);


        switch (ipq_message_type(buf)) {

            case NLMSG_ERROR: {
                fprintf(stderr, "Received error message %d\n",
                ipq_get_msgerr(buf));
                break;
            }
          case IPQM_PACKET:
 {
  ipq_packet_msg_t *m = ipq_get_packet(buf);


  struct iphdr *iph = ((struct iphdr *)m->payload);


  struct tcphdr *tcp = (struct tcphdr *)(m->payload + (iph->ihl << 2));

  struct udphdr *udp = (struct udphdr *) (m->payload + (iph->ihl << 2));

  int unsigned payload_offset = ((iph->ihl << 2) + (tcp->doff << 2));

    int unsigned payload_length = (unsigned int) ntohs(iph->tot_len) -
payload_offset;

//unsigned char data[2]={0x00,0x00};
unsigned char data[4]={0x00,0x00,0x01,0xb3};
 int i = 0;
while(m->data_len > 100) {


    if (m->payload[i] != 0x00) {
        i++;
                       }
    else {
    if (memcmp(&m->payload[i],data,sizeof(data)) == 0) {

            printf("I frame");

break;                                       }


     }
                }

status = ipq_set_verdict(h, m->packet_id,NF_ACCEPT, 0, NULL);

  break;
     }
    }



    }
    while (1);

    printf("Engine Stopped...\n");

    ipq_destroy_handle(h);

}

int main() {
    start_packet_engine();
    return 0;
}