The TCP Windows Scale option

The TCP Window Scale option, defined in RFC1323 and described in the TCP chapter of Computer Networking: Principles, Protocols and Practice allows endhosts to use a larger window than TCP's default 64 KBytes window.


Impact of the window scale option

The window scale option has been correctly negotiated on this connection. Assuming that that the client will use on the entire connection the same window size that it announced in the SYN, can you infer the value of the receive window that it will advertise inside its first segments ?

# Length Resumé Status
0 28 bytes <TCP: SYN, SEQ: 1395955212, ACK: 0, MSS, WSO>
1 28 bytes <TCP: ACK, SYN, SEQ: 2170178573, ACK: 1395955213, MSS, WSO>
2 20 bytes <TCP: ACK, SEQ: 1395955213, ACK: 2170178574>  
3 20 bytes <TCP: ACK, PSH, SEQ: 1395955213, ACK: 2170178574>  

0000  d1e804d25334960c  0000000070027080  
0010  4f940000020405a0  01030309          

0000  Ñè.ÒS4......p.p.
0010  O...........    
  • TCP:
    • Source Port: 53736
    • Destination Port: 1234
    • Sequence Number: 1395955212
    • Acknowledgment Number: 0
    • Data Offset: 7
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 0
    • PSH: 0
    • RST: 0
    • SYN: 1
    • FIN: 0
    • Window: 28800
    • Checksum: 20372
    • Urgent Pointer: 0
    • Options: Maximum Segment Size
      • Kind: 2
      • Length: 4
      • Max Seg Size: 1440
    • Options: No-Operation
      • Kind: 1
    • Options: Window Scale Option
      • Kind: 3
      • Length: 3
      • WSO: 9
0000  04d2d1e8815a4c0d  5334960d70127080  
0010  4f940000020405a0  01030309          

0000  .ÒÑè.ZL.S4..p.p.
0010  O...........    
  • TCP:
    • Source Port: 1234
    • Destination Port: 53736
    • Sequence Number: 2170178573
    • Acknowledgment Number: 1395955213
    • Data Offset: 7
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 1
    • FIN: 0
    • Window: 28800
    • Checksum: 20372
    • Urgent Pointer: 0
    • Options: Maximum Segment Size
      • Kind: 2
      • Length: 4
      • Max Seg Size: 1440
    • Options: No-Operation
      • Kind: 1
    • Options: Window Scale Option
      • Kind: 3
      • Length: 3
      • WSO: 9
0000  d1e804d25334960d  815a4c0e5010????  
0010  4f8c0000                            

0000  Ñè.ÒS4...ZL.P.??
0010  O...            
  • TCP:
    • Source Port: 53736
    • Destination Port: 1234
    • Sequence Number: 1395955213
    • Acknowledgment Number: 2170178574
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 0
    • RST: 0
    • SYN: 0
    • FIN: 0
    • Window:
    • Checksum: 20364
    • Urgent Pointer: 0
0000  d1e804d25334960d  815a4c0e5018????  
0010  4f8e0000                            

0000  Ñè.ÒS4...ZL.P.??
0010  O...            
  • TCP:
    • Source Port: 53736
    • Destination Port: 1234
    • Sequence Number: 1395955213
    • Acknowledgment Number: 2170178574
    • Data Offset: 5
    • Reserved: 0
    • NS: 0
    • CWR: 0
    • ECE: 0
    • URG: 0
    • ACK: 1
    • PSH: 1
    • RST: 0
    • SYN: 0
    • FIN: 0
    • Window:
    • Checksum: 20366
    • Urgent Pointer: 0

Information

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

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