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Author(s) Olivier Bonaventure
Deadline Keine Frist
Abgabenlimit No limitation
Category tags tcp

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Reordering the three-way-handshake

A TCP connection, as explained in the TCP chapter of Computer Networking: Principles, Protocols and Practice always starts with a three-way-handshake.


Three-way handshake

Can you correctly reorder the three segments that are used to establish a TCP connection ?

# Length Summary Status
0 24 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53718, Seq: 20522819, Ack: 4119273527, Len: 0
1 20 bytes Transmission Control Protocol, Src Port: 53718, Dst Port: 1234, Seq: 4119273527, Ack: 20522820, Len: 0
2 24 bytes Transmission Control Protocol, Src Port: 53718, Dst Port: 1234, Seq: 4119273526, Len: 0

0000  04d2d1d601392743  f587203760127080  
0010  00000000020405a0                    

0000  .ÒÑÖ.9'Cõ. 7`.p.
0010  ........        
  • Transmission Control Protocol, Src Port: 1234, Dst Port: 53718, Seq: 20522819, Ack: 4119273527, Len: 0
    • Source Port: 1234
      • Destination Port: 53718
        • Sequence number: 20522819
          • Acknowledgment number: 4119273527
            • 0110 .... = Header Length: 24 bytes (6)
              • Flags: 0x012 (SYN, 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
                            • .... .... 0... = Push: Not set
                              • .... .... .0.. = Reset: Not set
                                • .... .... ..1. = Syn: Set
                                  • .... .... ...0 = Fin: Not set
                                  • Window size value: 28800
                                    • Urgent pointer: 0
                                      • Options: (4 bytes), Maximum segment size
                                        • TCP Option - Maximum segment size: 1440 bytes
                                          • Kind: Maximum Segment Size (2)
                                            • Length: 4
                                              • MSS Value: 1440
                                          0000  d1d604d2f5872037  0139274450107080  
                                          0010  00000000                            

                                          0000  ÑÖ.Òõ. 7.9'DP.p.
                                          0010  ....            
                                          • Transmission Control Protocol, Src Port: 53718, Dst Port: 1234, Seq: 4119273527, Ack: 20522820, Len: 0
                                            • Source Port: 53718
                                              • Destination Port: 1234
                                                • Sequence number: 4119273527
                                                  • Acknowledgment number: 20522820
                                                    • 0101 .... = Header Length: 20 bytes (5)
                                                      • Flags: 0x010 (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
                                                                    • .... .... 0... = Push: Not set
                                                                      • .... .... .0.. = Reset: Not set
                                                                        • .... .... ..0. = Syn: Not set
                                                                          • .... .... ...0 = Fin: Not set
                                                                          • Window size value: 28800
                                                                            • Urgent pointer: 0
                                                                            0000  d1d604d2f5872036  0000000060027080  
                                                                            0010  00000000020405a0                    

                                                                            0000  ÑÖ.Òõ. 6....`.p.
                                                                            0010  ........        
                                                                            • Transmission Control Protocol, Src Port: 53718, Dst Port: 1234, Seq: 4119273526, Len: 0
                                                                              • Source Port: 53718
                                                                                • Destination Port: 1234
                                                                                  • Sequence number: 4119273526
                                                                                    • Acknowledgment number: 0
                                                                                      • 0110 .... = Header Length: 24 bytes (6)
                                                                                        • Flags: 0x002 (SYN)
                                                                                          • 000. .... .... = Reserved: Not set
                                                                                            • ...0 .... .... = Nonce: Not set
                                                                                              • .... 0... .... = Congestion Window Reduced (CWR): Not set
                                                                                                • .... .0.. .... = ECN-Echo: Not set
                                                                                                  • .... ..0. .... = Urgent: Not set
                                                                                                    • .... ...0 .... = Acknowledgment: Not set
                                                                                                      • .... .... 0... = Push: Not set
                                                                                                        • .... .... .0.. = Reset: Not set
                                                                                                          • .... .... ..1. = Syn: Set
                                                                                                            • .... .... ...0 = Fin: Not set
                                                                                                            • Window size value: 28800
                                                                                                              • Urgent pointer: 0
                                                                                                                • Options: (4 bytes), Maximum segment size
                                                                                                                  • TCP Option - Maximum segment size: 1440 bytes
                                                                                                                    • Kind: Maximum Segment Size (2)
                                                                                                                      • Length: 4
                                                                                                                        • MSS Value: 1440