Inferring acknowledgment numbers

TCP, as explained in the TCP chapter of Computer Networking: Principles, Protocols and Practice includes a sequence number in each segment that carries data and uses acknowledgements.

Paste this command into your terminal:

The password to connect is

Inferring acknowledgement numbers

During this connection, the client sent some data in successive segments and then the server replied with a an acknowledgement that confirms the reception of all the previous segments. Can you infer the acknowledgement number of the segment returned by the server ?

#	Length	Summary
0	28 bytes	`Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592493, Ack: 2477434132, Len: 8`
1	27 bytes	`Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592501, Ack: 2477434132, Len: 7`
2	29 bytes	`Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592508, Ack: 2477434132, Len: 9`
3	29 bytes	`Transmission Control Protocol, Src Port: 53710, Dst Port: 1234, Seq: 3378592517, Ack: 2477434132, Len: 9`
4	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: 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
- TCP payload (8 bytes)

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: 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
- TCP payload (7 bytes)

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: 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
- TCP payload (9 bytes)

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: 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
- 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: 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

Author(s)	Olivier Bonaventure
Deadline	Καμία προθεσμία
Submission limit	No limitation
Category tags	tcp

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