c++ - udp packet fragmentation for raw sockets -

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follow-up of question packet fragmentation raw sockets

if have raw socket implemented such:

  if ((sip_socket = socket(af_inet, sock_raw, ipproto_raw)) < 0)       {     cout << "unable create sip sockets."<< sip_socket<<" \n";     return -3;       }     if ( setsockopt(sip_socket, ipproto_ip, ip_hdrincl, &one, sizeof(one)) == -1)       {    cerr << "unable set option raw socket.\n";    return -4;       };

how can set iphdr->fragment_offset (16 bits including 3 bit flags) if have packet of size 1756 (not including ip header)?
need prepare 2 packets-one of size 1480 , of size 276, , slap ip headers on both packets?

can point example code this?

yes, need prepare 2 packets, each own ip header.

if put 1480 bytes of data in first packet , 276 in second, ip headers should identical, except these fields:

  • fragment offset: set 0 in first packet, , 1480 in second;
  • total length: set 1480 plus header length in first packet, , 276 plus header length in second packet;
  • mf flag: set 1 in first packet , 0 in second;
  • header checksum: recalculated on different headers appropriate.

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