The acknowledgement numbers in the three-way-handshake used by TCP - [CNP3] Computer Networking : Principles, Protocols and Practice | INGInious

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Author(s)	Olivier Bonaventure
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Category tags	tcp

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The acknowledgement numbers in the three-way-handshake used by TCP

The TCP header, shown in the TCP chapter of Computer Networking: Principles, Protocols and Practice contains a sequence number and an acknowledgement number. The three segments below correspond to the three-way handshake that is used to establish a TCP connection.

Paste this command into your terminal:

The password to connect is

Acknowledgement numbers

Can you infer the acknowledgement numbers of the second and third TCP segments exchanged in the three-way-handshake below ?

#	Length	Summary	Status
0	24 bytes	`Transmission Control Protocol, Src Port: 53712, Dst Port: 1234, Seq: 4207062859, Len: 0`
1	24 bytes	`Transmission Control Protocol, Src Port: 1234, Dst Port: 53712, Seq: 4037529898, Ack: ????, Len: 0`
2	20 bytes	`Transmission Control Protocol, Src Port: 53712, Dst Port: 1234, Seq: ????, Ack: ????, Len: 0`

0000 d1d004d2fac2af4b 0000000060027080
0010 4f900000020405a0

0000 ÑÐ.ÒúÂ¯K....`.p.
0010 O.......

Transmission Control Protocol, Src Port: 53712, Dst Port: 1234, Seq: 4207062859, Len: 0
- Source Port: 53712
- Destination Port: 1234
- TCP Segment Len: 0
- Sequence number: 4207062859
- 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
- Checksum: 0x4f90 [unverified]
- 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 04d2d1d0f0a7d12a ????????60127080
0010 4f900000020405a0

0000 .ÒÑÐð§Ñ*????`.p.
0010 O.......

Transmission Control Protocol, Src Port: 1234, Dst Port: 53712, Seq: 4037529898, Ack: ????, Len: 0
- Source Port: 1234
- Destination Port: 53712
- TCP Segment Len: 0
- Sequence number: 4037529898
- 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
  - .... .... ..1. = Syn: Set
  - .... .... ...0 = Fin: Not set
- Window size value: 28800
- Checksum: 0x4f90 [unverified]
- 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 d1d004d2???????? ????????50107080
0010 4f8c0000

0000 ÑÐ.Ò????????P.p.
0010 O...

Transmission Control Protocol, Src Port: 53712, Dst Port: 1234, Seq: ????, Ack: ????, Len: 0
- Source Port: 53712
- Destination Port: 1234
- TCP Segment Len: 0
- Sequence number: ?
- 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
- Checksum: 0x4f8c [unverified]
- Urgent pointer: 0