Question

我正在生成GTP隧道数据包，格式如下：

“Outter IP” - ＆gt; “Outter UDP” - ＆gt; “GTP” - ＆gt; “内部IP” - ＆gt; “内部UDP”

我正在使用的UDP校验和算法实际上来自DHCPd

**********************code snippet start **********************
udp_header->check = wrapsum(in_cksum((unsigned char *)udp_header, sizeof(struct udp_header),
                                       in_cksum((unsigned char *)&buffer[i], send_len-i,
                        in_cksum((unsigned char *)&ip_header->saddr,
                             2*sizeof(ip_header->saddr),
                             IPPROTO_UDP + ntohs(udp_header->len)))));

/* ******************************************* */

/*
 * Checksum routine for Internet Protocol family headers (C Version)
 *
 * Borrowed from DHCPd
 */

static u_int32_t in_cksum(unsigned char *buf,
              unsigned nbytes, u_int32_t sum) {
  uint i;

  /* Checksum all the pairs of bytes first... */
  for (i = 0; i < (nbytes & ~1U); i += 2) {
    sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
    /* Add carry. */
    if(sum > 0xFFFF)
      sum -= 0xFFFF;
  }

  /* If there's a single byte left over, checksum it, too.   Network
     byte order is big-endian, so the remaining byte is the high byte. */
  if(i < nbytes) {
#ifdef DEBUG_CHECKSUM_VERBOSE
    debug ("sum = %x", sum);
#endif
    sum += buf [i] << 8;
    /* Add carry. */
    if(sum > 0xFFFF)
      sum -= 0xFFFF;
  }

  return sum;
}

/* ******************************************* */

static u_int32_t wrapsum (u_int32_t sum) {
  sum = ~sum & 0xFFFF;
  return htons(sum);
}


**********************code snippet end**********************

outter UDP和内部UDP调用都使用相同的校验和函数。但是，我的内部UDP很好但是我的外部UDP没有通过wireshark的校验和检查。有没有人对此问题有任何建议？

隧道数据包的UDP校验和失败

0 个答案: