my $buff;
  defined(recv(SOCK,$buff,256,0)) or die "error: $! \n";
  print "received: ", length($buff), " bytes\n";
 
  my($type,$subcode,$cksum,$recv_pid,$recv_seq)=unpack(ICMP_STRUCT,substr($buff,20));
   if($type == ICMP_ECHOREPLY) {

    if($recv_pid != $pid) {

      print "icmp reply ignored (different pid) \n";
    }
    elsif($recv_seq != $seq) {
      print "icmp reply ignored (different seq) \n";
    }
    else {print "got icmp reply \n"};
    }
  else {
    print "not an icmp reply\n";
  }
}