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Author(s) Olivier Bonaventure
Deadline No deadline
Submission limit No limitation
Category tags TCP

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TCP simultaneous establishment


TCP simultaneous connection establishment

Under specific circumstances, two TCP hosts can send a SYN segment at the same time. In this case, the establishment of a connection requires the transmission of four segments. Can you fill the missing fields of these four segments ?

# Length Summary Status
0 24 bytes Transmission Control Protocol, Src Port: 43494, Dst Port: 8080, Seq: 4224100836, Len: 0  
1 24 bytes Transmission Control Protocol, Src Port: 8080, Dst Port: 43494, Seq: 0, Len: 0  
2 24 bytes Transmission Control Protocol, Src Port: 43494, Dst Port: 8080, Seq: 4224100836, Ack: ????, Len: 0  
3 20 bytes Transmission Control Protocol, Src Port: 8080, Dst Port: 43494, Seq: 1, Ack: ????, Len: 0  

0000  a9e61f90fbc6a9e4  0000000060??4e20  
0010  021c0000020403e8                    

0000  ©æ..ûÆ©ä....`?N
0010  .......è        
  • Transmission Control Protocol, Src Port: 43494, Dst Port: 8080, Seq: 4224100836, Len: 0
    • Source Port: 43494
      • Destination Port: 8080
        • TCP Segment Len: 0
          • Sequence number: 4224100836
            • 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
                                  • .... .... ..?. = Syn: ?
                                  • .... .... ...0 = Fin: Not set
                                  • Window size value: 20000
                                    • Calculated window size: 20000
                                      • Checksum: 0x021c [unverified]
                                        • Urgent pointer: 0
                                          • Options: (4 bytes), Maximum segment size
                                            • TCP Option - Maximum segment size: 1000 bytes
                                              • Kind: Maximum Segment Size (2)
                                                • Length: 4
                                                  • MSS Value: 1000
                                              0000  1f90a9e600000000  0000000060??16a0  
                                              0010  b7de0000020403e8                    

                                              0000  ..©æ........`?..
                                              0010  ·Þ.....è        
                                              • Transmission Control Protocol, Src Port: 8080, Dst Port: 43494, Seq: 0, Len: 0
                                                • Source Port: 8080
                                                  • Destination Port: 43494
                                                    • TCP Segment Len: 0
                                                      • Sequence number: 0
                                                        • 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
                                                                              • .... .... ..?. = Syn: ?
                                                                              • .... .... ...0 = Fin: Not set
                                                                              • Window size value: 5792
                                                                                • Calculated window size: 5792
                                                                                  • Checksum: 0xb7de [unverified]
                                                                                    • Urgent pointer: 0
                                                                                      • Options: (4 bytes), Maximum segment size
                                                                                        • TCP Option - Maximum segment size: 1000 bytes
                                                                                          • Kind: Maximum Segment Size (2)
                                                                                            • Length: 4
                                                                                              • MSS Value: 1000
                                                                                          0000  a9e61f90fbc6a9e4  ????????60??4e20  
                                                                                          0010  021c0000020403e8                    

                                                                                          0000  ©æ..ûÆ©ä????`?N
                                                                                          0010  .......è        
                                                                                          • Transmission Control Protocol, Src Port: 43494, Dst Port: 8080, Seq: 4224100836, Ack: ????, Len: 0
                                                                                            • Source Port: 43494
                                                                                              • Destination Port: 8080
                                                                                                • TCP Segment Len: 0
                                                                                                  • Sequence number: 4224100836
                                                                                                    • Acknowledgment number: ?
                                                                                                    • 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
                                                                                                                        • .... .... ..?. = Syn: ?
                                                                                                                        • .... .... ...0 = Fin: Not set
                                                                                                                        • Window size value: 20000
                                                                                                                          • Calculated window size: 20000
                                                                                                                            • Checksum: 0x021c [unverified]
                                                                                                                              • Urgent pointer: 0
                                                                                                                                • Options: (4 bytes), Maximum segment size
                                                                                                                                  • TCP Option - Maximum segment size: 1000 bytes
                                                                                                                                    • Kind: Maximum Segment Size (2)
                                                                                                                                      • Length: 4
                                                                                                                                        • MSS Value: 1000
                                                                                                                                    0000  1f90a9e600000001  ????????50??16a0  
                                                                                                                                    0010  28130000                            

                                                                                                                                    0000  ..©æ....????P?..
                                                                                                                                    0010  (...            
                                                                                                                                    • Transmission Control Protocol, Src Port: 8080, Dst Port: 43494, Seq: 1, Ack: ????, Len: 0
                                                                                                                                      • Source Port: 8080
                                                                                                                                        • Destination Port: 43494
                                                                                                                                          • TCP Segment Len: 0
                                                                                                                                            • Sequence number: 1
                                                                                                                                              • Acknowledgment number: ?
                                                                                                                                              • 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
                                                                                                                                                                  • .... .... ..?. = Syn: ?
                                                                                                                                                                  • .... .... ...0 = Fin: Not set
                                                                                                                                                                  • Window size value: 5792
                                                                                                                                                                    • Calculated window size: 5792
                                                                                                                                                                      • Window size scaling factor: -2 (no window scaling used)
                                                                                                                                                                        • Checksum: 0x2813 [unverified]
                                                                                                                                                                          • Urgent pointer: 0