udp原始套接字的数据包分片

问题描述：

如果我有一个原始套接字实现这样：

If I have a raw socket implemented as such:

  if ((sip_socket = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0)
      {
    cout << "Unable to create the SIP sockets."<< sip_socket<<" \n";
    return -3;
      }

   if ( setsockopt(sip_socket, IPPROTO_IP, IP_HDRINCL, &one, sizeof(one)) == -1)
      {
   cerr << "Unable to set option to Raw Socket.\n";
   return -4;
      };

如何设置 ipHdr-> fragment_offset 如果我有一个大小为1756的数据包（不包括IP头）？

我需要准备两个数据包 - 一个大小1480和另一个大小276，然后打IP报头两个包？

how can I set the ipHdr->fragment_offset (16 bits including 3 bit flags) if I have a packet of size 1756 (not including the IP header)?
Do I need to prepare two packets-one of size 1480 and another of size 276, and then slap IP headers on both packets?

任何人都可以指向此示例代码？

Can anyone point to an example code for this?

答

是的，您需要准备两个数据包，每个数据包都有自己的IP头。

Yes, you need to prepare two packets, each with their own IP header.

如果你把第一个包中的1480字节的数据和第二个包中的276个数据，那么IP头应该是相同的，除了这些字段：

If you put 1480 bytes of data in the first packet and 276 in the second, then the IP headers should be identical, except for these fields:

Fragment Offset ：在第一个数据包中设置为 0 ， 1480 在第二个;

总长：设置为1480加上第一个分组，276加上第二个分组中的头长度;

MF 标志：设置为 1 c> c>

第一个数据包中的 / code>：根据需要重新计算不同的标题。

Fragment Offset: set to 0 in the first packet, and 1480 in the second;
Total Length: set to 1480 plus the header length in the first packet, and 276 plus the header length in the second packet;
MF flag: set to 1 in the first packet and 0 in the second;
Header Checksum: Recalculated over the different headers as appropriate.

udp原始套接字的数据包分片

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