Utilisation of the SYN and ACK flags during the three-way-handshake used by TCP

The TCP header, shown in the TCP chapter of Computer Networking: Principles, Protocols and Practice contains several flags, including the SYN and the ACK flags. These two flags play an important role during the establishment of a connection. 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 value of the SYN and ACK flags in the three segments below ?

#	Length	Summary
0	24 bytes	`Transmission Control Protocol, Src Port: 53708, Dst Port: 1234, Seq: 2250678587, Len: 0`
1	24 bytes	`Transmission Control Protocol, Src Port: 1234, Dst Port: 53708, Seq: 3164923748, Ack: 2250678588, Len: 0`
2	20 bytes	`Transmission Control Protocol, Src Port: 53708, Dst Port: 1234, Seq: 2250678588, Ack: 3164923749, Len: 0`

0000 d1cc04d28626a13b 0000000060??7080
0010 00000000020405a0

0000 ÑÌ.Ò.&¡;....`?p.
0010 ........

Transmission Control Protocol, Src Port: 53708, Dst Port: 1234, Seq: 2250678587, Len: 0
- Source Port: 53708
- Destination Port: 1234
- Sequence number: 2250678587
- Acknowledgment number: 0
- 0110 .... = Header Length: 24 bytes (6)
- 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
  - .... ...? .... = Acknowledgment: ?
  - .... .... 0... = Push: Not set
  - .... .... .0.. = Reset: Not set
  - .... .... ..?. = Syn: ?
  - .... .... ...0 = Fin: Not set
- Window size value: 28800
- 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 04d2d1ccbca4e764 8626a13c60??7080
0010 00000000020405a0

0000 .ÒÑÌ¼¤çd.&¡<`?p.
0010 ........

Transmission Control Protocol, Src Port: 1234, Dst Port: 53708, Seq: 3164923748, Ack: 2250678588, Len: 0
- Source Port: 1234
- Destination Port: 53708
- Sequence number: 3164923748
- Acknowledgment number: 2250678588
- 0110 .... = Header Length: 24 bytes (6)
- 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
  - .... ...? .... = Acknowledgment: ?
  - .... .... 0... = Push: Not set
  - .... .... .0.. = Reset: Not set
  - .... .... ..?. = Syn: ?
  - .... .... ...0 = Fin: Not set
- Window size value: 28800
- 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 d1cc04d28626a13c bca4e76550??7080
0010 00000000

0000 ÑÌ.Ò.&¡<¼¤çeP?p.
0010 ....

Transmission Control Protocol, Src Port: 53708, Dst Port: 1234, Seq: 2250678588, Ack: 3164923749, Len: 0
- Source Port: 53708
- Destination Port: 1234
- Sequence number: 2250678588
- Acknowledgment number: 3164923749
- 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
  - .... ...? .... = Acknowledgment: ?
  - .... .... 0... = Push: Not set
  - .... .... .0.. = Reset: Not set
  - .... .... ..?. = Syn: ?
  - .... .... ...0 = Fin: Not set
- Window size value: 28800
- Urgent pointer: 0

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

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