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Tác giả Olivier Bonaventure
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The TCP header length

The TCP header, shown in the TCP chapter of Computer Networking: Principles, Protocols and Practice contains a TCP Header Length or Data Offset field that indicates the start of the payload of a TCP segment.

TCP Header Length

The TCP segment was sent inside an IPv6 packet whose payload length is set to 34 bytes. Can you recompute its TCP Header Length (the calculated value in bytes, not the Data Offset one) ?

# Length Summary Status
0 34 bytes Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389304, Ack: 2100570799, Len: 2  
0000  d20004d2a7832338  7d342aaf??187080  
0010  000000000101080a  000476b10004759d  
0020  610a                                
0000  Ò..Ò§.#8}4*¯?.p.
0010  ..........v±..u.
0020  a.              
  • Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389304, Ack: 2100570799, Len: 2
    • Source Port: 53760
      • Destination Port: 1234
        • Sequence number: 2810389304
          • Acknowledgment number: 2100570799
            • ???? .... = Header Length: ?
            • Flags: 0x018 (PSH, ACK)
              • 000. .... .... = Reserved: Not set
                • ...0 .... .... = Nonce: Not set
                  • .... 0... .... = Congestion Window Reduced (CWR): Not set
                    • .... .0.. .... = ECN-Echo: Not set
                      • .... ..0. .... = Urgent: Not set
                        • .... ...1 .... = Acknowledgment: Set
                          • .... .... 1... = Push: Set
                            • .... .... .0.. = Reset: Not set
                              • .... .... ..0. = Syn: Not set
                                • .... .... ...0 = Fin: Not set
                                • Window size value: 28800
                                  • Urgent pointer: 0
                                    • Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
                                      • TCP Option - No-Operation (NOP)
                                        • Kind: No-Operation (1)
                                        • TCP Option - No-Operation (NOP)
                                          • Kind: No-Operation (1)
                                          • TCP Option - Timestamps: TSval 292529, TSecr 292253
                                            • Kind: Time Stamp Option (8)
                                              • Length: 10
                                                • Timestamp value: 292529
                                                  • Timestamp echo reply: 292253
                                                • TCP payload (2 bytes)