Utilisation of the FIN flag

TCP segments contain flags. These are defined in Section 3.1 of RFC793.

The packet trace below corresponds to the establishment of a TCP connection by a client that sent one byte of data and then decided to close the connection immediately.


Utilisation of the `FIN` flag

In this trace, can you infer which segments had their FIN flag set ?

# Length Resumé Status
0 24 bytes <TCP: SYN, SEQ: 3405899000, ACK: 0, MSS>
1 24 bytes <TCP: ACK, SYN, SEQ: 2186540616, ACK: 3405899001, MSS>
2 20 bytes <TCP: ACK, SEQ: 3405899001, ACK: 2186540617>
3 21 bytes <TCP: ACK, PSH, SEQ: 3405899001, ACK: 2186540617>  
4 20 bytes <TCP: ACK, SEQ: 2186540617, ACK: 3405899002>  
5 20 bytes <TCP: ACK, SEQ: 3405899002, ACK: 2186540617>  
6 20 bytes <TCP: ACK, SEQ: 2186540617, ACK: 3405899003>  
7 20 bytes <TCP: ACK, SEQ: 3405899003, ACK: 2186540618>  

0000  d1d404d2cb01e4f8  0000000060027080  
0010  4f900000020405a0                    

0000  ÑÔ.ÒË.äø....`.p.
0010  O.......        
  • TCP:
    • Source Port: 53716
    • Destination Port: 1234
    • Sequence Number: 3405899000
    • Acknowledgment Number: 0
    • Data Offset: 6
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 0
    • PSH: 0
    • RST: 0
    • SYN: 1
    • FIN: 0
    • Window: 28800
    • Checksum: 20368
    • Urgent Pointer: 0
    • Options: Maximum Segment Size
      • Kind: 2
      • Length: 4
      • Max Seg Size: 1440
0000  04d2d1d48253f648  cb01e4f960127080  
0010  4f900000020405a0                    

0000  .ÒÑÔ.SöHË.äù`.p.
0010  O.......        
  • TCP:
    • Source Port: 1234
    • Destination Port: 53716
    • Sequence Number: 2186540616
    • Acknowledgment Number: 3405899001
    • Data Offset: 6
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 1
    • FIN: 0
    • Window: 28800
    • Checksum: 20368
    • Urgent Pointer: 0
    • Options: Maximum Segment Size
      • Kind: 2
      • Length: 4
      • Max Seg Size: 1440
0000  d1d404d2cb01e4f9  8253f64950107080  
0010  4f8c0000                            

0000  ÑÔ.ÒË.äù.SöIP.p.
0010  O...            
  • TCP:
    • Source Port: 53716
    • Destination Port: 1234
    • Sequence Number: 3405899001
    • Acknowledgment Number: 2186540617
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN: 0
    • Window: 28800
    • Checksum: 20364
    • Urgent Pointer: 0
0000  d1d404d2cb01e4f9  8253f64950??7080  
0010  4f8d00000a                          

0000  ÑÔ.ÒË.äù.SöIP?p.
0010  O....           
  • TCP:
    • Source Port: 53716
    • Destination Port: 1234
    • Sequence Number: 3405899001
    • Acknowledgment Number: 2186540617
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 1
    • RST: 0
    • SYN: 0
    • FIN:
    • Window: 28800
    • Checksum: 20365
    • Urgent Pointer: 0
    • Data: bytearray(b'\n')
0000  04d2d1d48253f649  cb01e4fa50??7080  
0010  4f8c0000                            

0000  .ÒÑÔ.SöIË.äúP?p.
0010  O...            
  • TCP:
    • Source Port: 1234
    • Destination Port: 53716
    • Sequence Number: 2186540617
    • Acknowledgment Number: 3405899002
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN:
    • Window: 28800
    • Checksum: 20364
    • Urgent Pointer: 0
0000  d1d404d2cb01e4fa  8253f64950??7080  
0010  4f8c0000                            

0000  ÑÔ.ÒË.äú.SöIP?p.
0010  O...            
  • TCP:
    • Source Port: 53716
    • Destination Port: 1234
    • Sequence Number: 3405899002
    • Acknowledgment Number: 2186540617
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN:
    • Window: 28800
    • Checksum: 20364
    • Urgent Pointer: 0
0000  04d2d1d48253f649  cb01e4fb50??7080  
0010  4f8c0000                            

0000  .ÒÑÔ.SöIË.äûP?p.
0010  O...            
  • TCP:
    • Source Port: 1234
    • Destination Port: 53716
    • Sequence Number: 2186540617
    • Acknowledgment Number: 3405899003
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN:
    • Window: 28800
    • Checksum: 20364
    • Urgent Pointer: 0
0000  d1d404d2cb01e4fb  8253f64a50??7080  
0010  4f8c0000                            

0000  ÑÔ.ÒË.äû.SöJP?p.
0010  O...            
  • TCP:
    • Source Port: 53716
    • Destination Port: 1234
    • Sequence Number: 3405899003
    • Acknowledgment Number: 2186540618
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN:
    • Window: 28800
    • Checksum: 20364
    • Urgent Pointer: 0

Information

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

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