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

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The TCP Timestamp option

The TCP Timestamp option, defined in RFC1323 and described in the TCP chapter of Computer Networking: Principles, Protocols and Practice allows endhosts to exchange timestamp information.


Negotiation of the TCP Timestamp option

Assuming that the server supports the timestamp option, can you predict the value of the TS Echo Reply field in both segments ?

# Length Summary Status
0 36 bytes Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389303, Len: 0  
1 36 bytes Transmission Control Protocol, Src Port: 1234, Dst Port: 53760, Seq: 2100570798, Ack: 2810389304, Len: 0  

0000  d20004d2a7832337  0000000090027080  
0010  00000000020405a0  0101080a0004759c  
0020  ????????                            

0000  Ò..Ò§.#7......p.
0010  ..............u.
0020  ????            
  • Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389303, Len: 0
    • Source Port: 53760
      • Destination Port: 1234
        • Sequence number: 2810389303
          • Acknowledgment number: 0
            • 1001 .... = Header Length: 36 bytes (9)
              • 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: (16 bytes), Maximum segment size, No-Operation (NOP), No-Operation (NOP), Timestamps
                                        • TCP Option - Maximum segment size: 1440 bytes
                                          • Kind: Maximum Segment Size (2)
                                            • Length: 4
                                              • MSS Value: 1440
                                              • TCP Option - No-Operation (NOP)
                                                • Kind: No-Operation (1)
                                                • TCP Option - No-Operation (NOP)
                                                  • Kind: No-Operation (1)
                                                  • TCP Option - Timestamps: TSval 292252, TSecr ????
                                                    • Kind: Time Stamp Option (8)
                                                      • Length: 10
                                                        • Timestamp value: 292252
                                                          • Timestamp echo reply: ?
                                                    0000  04d2d2007d342aae  a783233890126f90  
                                                    0010  00000000020405a0  0101080a0004759d  
                                                    0020  ????????                            

                                                    0000  .ÒÒ.}4*®§.#8..o.
                                                    0010  ..............u.
                                                    0020  ????            
                                                    • Transmission Control Protocol, Src Port: 1234, Dst Port: 53760, Seq: 2100570798, Ack: 2810389304, Len: 0
                                                      • Source Port: 1234
                                                        • Destination Port: 53760
                                                          • Sequence number: 2100570798
                                                            • Acknowledgment number: 2810389304
                                                              • 1001 .... = Header Length: 36 bytes (9)
                                                                • 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: 28560
                                                                                      • Urgent pointer: 0
                                                                                        • Options: (16 bytes), Maximum segment size, No-Operation (NOP), No-Operation (NOP), Timestamps
                                                                                          • TCP Option - Maximum segment size: 1440 bytes
                                                                                            • Kind: Maximum Segment Size (2)
                                                                                              • Length: 4
                                                                                                • MSS Value: 1440
                                                                                                • TCP Option - No-Operation (NOP)
                                                                                                  • Kind: No-Operation (1)
                                                                                                  • TCP Option - No-Operation (NOP)
                                                                                                    • Kind: No-Operation (1)
                                                                                                    • TCP Option - Timestamps: TSval 292253, TSecr ????
                                                                                                      • Kind: Time Stamp Option (8)
                                                                                                        • Length: 10
                                                                                                          • Timestamp value: 292253
                                                                                                            • Timestamp echo reply: ?