struct iphdr
  {
#if __BYTE_ORDER == __LITTLE_ENDIAN
    u_int8_t ihl:4;
    u_int8_t version:4;
#elif __BYTE_ORDER == __BIG_ENDIAN
    u_int8_t	version:4;
    u_int8_t ihl:4;
#else
#error	"Please fix <bytesex.h>"
#endif
    u_int8_t tos;
    u_int16_t tot_len;
    u_int16_t id;
    u_int16_t frag_off;
    u_int8_t ttl;
    u_int8_t protocol;
    u_int16_t check;
    u_int32_t saddr;
    u_int32_t daddr;
  };