[网络协议]tcp 连接校验和注意点

tcp 连接校验和注意点

1. psd结构体
   struct psd_header
   {
   unsigned int saddr; //源地址 大端
   unsigned int daddr; //目的地址 大端
   char mbz; //强制置空
   char ptcl; //协议类型
   unsigned short tcpl; //TCP长度 大端
   };
2. tcp 头结构体
   /**

• TCP Header
  */
  struct rte_tcp_hdr {
  rte_be16_t src_port; /< TCP source port. */
  rte_be16_t dst_port; /< TCP destination port. */
  rte_be32_t sent_seq; /< TX data sequence number. */
  rte_be32_t recv_ack; /< RX data acknowledgment sequence number. */
  uint8_t data_off; /< Data offset. */
  uint8_t tcp_flags; /< TCP flags */
  rte_be16_t rx_win; /< RX flow control window. */
  rte_be16_t cksum; /< TCP checksum. */
  rte_be16_t tcp_urp; /**< TCP urgent pointer, if any. */
  } __rte_packed;

3. 发送SYN包时，校验和需要注意OPTION选项值，必须要加上，见下图标记
   

4. 发送SYN包计算校验和示例
   unsigned char tcp_opt_test[]={0x02 ,0x04 ,0x05 ,0xb4 ,0x01 ,0x03 ,0x03 ,0x02 ,0x01 ,0x01 ,0x04 ,0x02};
   uint16_t option_len = sizeof(tcp_opt_test);
   unsigned char psd[512] = {0};
   *(uint32_t *)(psd) = src_addr;
   *(uint32_t *)(psd + 4) = dst_addr;
   *(unsigned char *)(psd + 8) = 0;
   *(unsigned char *)(psd + 9) = IPPROTO_TCP;
   *(uint16_t )(psd + 10) = rte_cpu_to_be_16(sizeof(struct rte_tcp_hdr)+option_len);
   (struct rte_tcp_hdr)(psd + 12) = tcp_hdr; //tcp 头部参数
   unsigned char psd_p = (unsigned char)(psd + 12 + sizeof(struct rte_tcp_hdr));
   for (auto i = 0; i != sizeof(tcp_opt); ++i)
   {
   *(psd_p + i) = tcp_opt [i];
   }

    uint16_t  check_sum = 0;
    check_sum = ip_sum((uint16_t *)psd, sizeof(struct rte_tcp_hdr) + sizeof(struct psd_header) + option_len);    //tcp 校验和
   

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