The TCP Timestamp option - [CNP3] Computer Networking : Principles, Protocols and Practice | INGInious

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Auteur(s)	Olivier Bonaventure
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Étiquettes de catégories	tcp

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The TCP Timestamp option

The TCP Timestamp option, defined in RFC1323 and described in the TCP chapter of Computer Networking: Principles, Protocols and Practice allows endhosts to exchange timestamp information.

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Negotiation of the TCP Timestamp option

Assuming that the server supports the timestamp option, can you predict the value of the TS Echo Reply field in both segments ?

#	Taille	Résumé	État
0	36 octets	`Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389303, Len: 0`
1	36 octets	`Transmission Control Protocol, Src Port: 1234, Dst Port: 53760, Seq: 2100570798, Ack: 2810389304, Len: 0`

0000  d20004d2a7832337  0000000090027080
0010  00000000020405a0  0101080a0004759c
0020  ????????

0000  Ò..Ò§.#7......p.
0010  ..............u.
0020  ????

Transmission Control Protocol, Src Port: 53760, Dst Port: 1234, Seq: 2810389303, Len: 0
- Source Port: 53760
- Destination Port: 1234
- Sequence number: 2810389303
- Acknowledgment number: 0
- 1001 .... = Header Length: 36 bytes (9)
- 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
- Urgent pointer: 0
- Options: (16 bytes), Maximum segment size, No-Operation (NOP), No-Operation (NOP), Timestamps
  - TCP Option - Maximum segment size: 1440 bytes
    - Kind: Maximum Segment Size (2)
    - Length: 4
    - MSS Value: 1440
  - TCP Option - No-Operation (NOP)
    - Kind: No-Operation (1)
  - TCP Option - No-Operation (NOP)
    - Kind: No-Operation (1)
  - TCP Option - Timestamps: TSval 292252, TSecr ????
    - Kind: Time Stamp Option (8)
    - Length: 10
    - Timestamp value: 292252
    - Timestamp echo reply: ?

0000  04d2d2007d342aae  a783233890126f90
0010  00000000020405a0  0101080a0004759d
0020  ????????

0000  .ÒÒ.}4*®§.#8..o.
0010  ..............u.
0020  ????

Transmission Control Protocol, Src Port: 1234, Dst Port: 53760, Seq: 2100570798, Ack: 2810389304, Len: 0
- Source Port: 1234
- Destination Port: 53760
- Sequence number: 2100570798
- Acknowledgment number: 2810389304
- 1001 .... = Header Length: 36 bytes (9)
- 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: 28560
- Urgent pointer: 0
- Options: (16 bytes), Maximum segment size, No-Operation (NOP), No-Operation (NOP), Timestamps
  - TCP Option - Maximum segment size: 1440 bytes
    - Kind: Maximum Segment Size (2)
    - Length: 4
    - MSS Value: 1440
  - TCP Option - No-Operation (NOP)
    - Kind: No-Operation (1)
  - TCP Option - No-Operation (NOP)
    - Kind: No-Operation (1)
  - TCP Option - Timestamps: TSval 292253, TSecr ????
    - Kind: Time Stamp Option (8)
    - Length: 10
    - Timestamp value: 292253
    - Timestamp echo reply: ?