Information

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

Tags

Sign in

TCP acknowledgements

The TCP header, shown in the TCP chapter of Computer Networking: Principles, Protocols and Practice contains an acknowledgement number.


Sequence numbers

A data transfer has started with a three-way handshake that is not shown in this trace. Can you infer the acknowledgements numbers of the two missing segments in the trace below ?

# Length Summary Status
0 28 bytes Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592493, Ack: 2477434132, Len: 8
1 20 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: 3378592501, Len: 0
2 27 bytes Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592501, Ack: 2477434132, Len: 7
3 20 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: ??, Len: 0  
4 29 bytes Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592508, Ack: 2477434132, Len: 9
5 20 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: 3378592517, Len: 0
6 29 bytes Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592517, Ack: 2477434132, Len: 9
7 20 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: ????, Len: 0  

0000  d1ce04d2c9613aed  93aaa51450187080  
0010  0000000073647173  6473710a          

0000  ÑÎ.ÒÉa:í.ª¥.P.p.
0010  ....sdqsdsq.    
  • Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592493, Ack: 2477434132, Len: 8
    • Source Port: 53710
      • Destination Port: 1234
        • Sequence number: 3378592493
          • Acknowledgment number: 2477434132
            • 0101 .... = Header Length: 20 bytes (5)
              • Flags
                • 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
                                      • TCP payload (8 bytes)
                                      0000  04d2d1ce93aaa514  c9613af550107080  
                                      0010  00000000                            

                                      0000  .ÒÑÎ.ª¥.Éa:õP.p.
                                      0010  ....            
                                      • Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: 3378592501, Len: 0
                                        • Source Port: 1234
                                          • Destination Port: 53710
                                            • Sequence number: 2477434132
                                              • Acknowledgment number: 3378592501
                                                • 0101 .... = Header Length: 20 bytes (5)
                                                  • Flags
                                                    • 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  d1ce04d2c9613af5  93aaa51450187080  
                                                                        0010  0000000073716471  73640a            

                                                                        0000  ÑÎ.ÒÉa:õ.ª¥.P.p.
                                                                        0010  ....sqdqsd.     
                                                                        • Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592501, Ack: 2477434132, Len: 7
                                                                          • Source Port: 53710
                                                                            • Destination Port: 1234
                                                                              • Sequence number: 3378592501
                                                                                • Acknowledgment number: 2477434132
                                                                                  • 0101 .... = Header Length: 20 bytes (5)
                                                                                    • Flags
                                                                                      • 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
                                                                                                            • TCP payload (7 bytes)
                                                                                                            0000  04d2d1ce93aaa514  ????????50107080  
                                                                                                            0010  00000000                            

                                                                                                            0000  .ÒÑÎ.ª¥.????P.p.
                                                                                                            0010  ....            
                                                                                                            • Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: ??, Len: 0
                                                                                                              • Source Port: 1234
                                                                                                                • Destination Port: 53710
                                                                                                                  • Sequence number: 2477434132
                                                                                                                    • Acknowledgment number: ?
                                                                                                                    • 0101 .... = Header Length: 20 bytes (5)
                                                                                                                      • Flags
                                                                                                                        • 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  d1ce04d2c9613afc  93aaa51450187080  
                                                                                                                                            0010  0000000073716471  736473710a        

                                                                                                                                            0000  ÑÎ.ÒÉa:ü.ª¥.P.p.
                                                                                                                                            0010  ....sqdqsdsq.   
                                                                                                                                            • Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592508, Ack: 2477434132, Len: 9
                                                                                                                                              • Source Port: 53710
                                                                                                                                                • Destination Port: 1234
                                                                                                                                                  • Sequence number: 3378592508
                                                                                                                                                    • Acknowledgment number: 2477434132
                                                                                                                                                      • 0101 .... = Header Length: 20 bytes (5)
                                                                                                                                                        • Flags
                                                                                                                                                          • 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
                                                                                                                                                                                • TCP payload (9 bytes)
                                                                                                                                                                                0000  04d2d1ce93aaa514  c9613b0550107080  
                                                                                                                                                                                0010  00000000                            

                                                                                                                                                                                0000  .ÒÑÎ.ª¥.Éa;.P.p.
                                                                                                                                                                                0010  ....            
                                                                                                                                                                                • Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: 3378592517, Len: 0
                                                                                                                                                                                  • Source Port: 1234
                                                                                                                                                                                    • Destination Port: 53710
                                                                                                                                                                                      • Sequence number: 2477434132
                                                                                                                                                                                        • Acknowledgment number: 3378592517
                                                                                                                                                                                          • 0101 .... = Header Length: 20 bytes (5)
                                                                                                                                                                                            • Flags
                                                                                                                                                                                              • 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  d1ce04d2c9613b05  93aaa51450187080  
                                                                                                                                                                                                                  0010  0000000073716473  716473710a        

                                                                                                                                                                                                                  0000  ÑÎ.ÒÉa;..ª¥.P.p.
                                                                                                                                                                                                                  0010  ....sqdsqdsq.   
                                                                                                                                                                                                                  • Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592517, Ack: 2477434132, Len: 9
                                                                                                                                                                                                                    • Source Port: 53710
                                                                                                                                                                                                                      • Destination Port: 1234
                                                                                                                                                                                                                        • Sequence number: 3378592517
                                                                                                                                                                                                                          • Acknowledgment number: 2477434132
                                                                                                                                                                                                                            • 0101 .... = Header Length: 20 bytes (5)
                                                                                                                                                                                                                              • Flags
                                                                                                                                                                                                                                • 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
                                                                                                                                                                                                                                                      • TCP payload (9 bytes)
                                                                                                                                                                                                                                                      0000  04d2d1ce93aaa514  ????????50107080  
                                                                                                                                                                                                                                                      0010  00000000                            

                                                                                                                                                                                                                                                      0000  .ÒÑÎ.ª¥.????P.p.
                                                                                                                                                                                                                                                      0010  ....            
                                                                                                                                                                                                                                                      • Transmission Control Protocol, Src Port: 1234, Dst Port: 53710, Seq: 2477434132, Ack: ????, Len: 0
                                                                                                                                                                                                                                                        • Source Port: 1234
                                                                                                                                                                                                                                                          • Destination Port: 53710
                                                                                                                                                                                                                                                            • Sequence number: 2477434132
                                                                                                                                                                                                                                                              • Acknowledgment number: ?
                                                                                                                                                                                                                                                              • 0101 .... = Header Length: 20 bytes (5)
                                                                                                                                                                                                                                                                • Flags
                                                                                                                                                                                                                                                                  • 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