RFC 6038, "Two-Way Active Measurement Protocol (TWAMP) Reflect Octets and Symmetrical Size Features", October 2010

Errata ID: 6408
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Nikolai Malykh
Date Reported: 2021-01-25
Verifier Name: Martin Duke
Date Verified: 2021-01-26

Section 5.1.3 says:

   When using the truncation process in TWAMP alone, see Section 4.2.1
   of [RFC5357], the Session-Sender MUST append sufficient Packet
   Padding octets to allow the same IP packet payload lengths to be used
   in each direction of transmission (this is usually desirable).  To
   compensate for the Session-Reflector's larger test packet format, the
   Session-Sender MUST append at least 27 octets of padding in
   Unauthenticated mode, and at least 56 octets in Authenticated and
   Encrypted modes.  The sizes of TWAMP-Test protocol packets and the
   resulting truncated padding to achieve equal packet sizes in both
   directions are shown in the table below:









Morton & Ciavattone          Standards Track                   [Page 11]

RFC 6038             Reflect Octets & Symmetric Size        October 2010


    +-------------------+----------------------+---------------------+
    | Octets in:        | Unauthenticated Mode | Auth/Encrypted Mode |
    +-------------------+----------------------+---------------------+
    | Reflector Header  | 41                   | 104                 |
    | Sender Header     | 14                   | 48                  |
    | Truncated Padding | 27                   | 56                  |
    +-------------------+----------------------+---------------------+

                       TWAMP-Test Padding Truncation

   When using the Reflect Octets mode simultaneously with the truncation
   process that TWAMP recommends in Section 4.2.1 of [RFC5357], the
   Session-Sender MUST append at least 27 octets of padding plus the
   Length of the padding to reflect octets when operating in
   Unauthenticated mode.  The Session-Sender MUST append at least 56
   octets of padding plus the Length of the padding to reflect octets
   when operating in Authenticated and Encrypted modes.

It should say:

   When using the truncation process in TWAMP alone, see Section 4.2.1
   of [RFC5357], the Session-Sender MUST append sufficient Packet
   Padding octets to allow the same IP packet payload lengths to be used
   in each direction of transmission (this is usually desirable).  To
   compensate for the Session-Reflector's larger test packet format, the
   Session-Sender MUST append at least 27 octets of padding in
   Unauthenticated mode, and at least 64 octets in Authenticated and
   Encrypted modes.  The sizes of TWAMP-Test protocol packets and the
   resulting truncated padding to achieve equal packet sizes in both
   directions are shown in the table below:









Morton & Ciavattone          Standards Track                   [Page 11]

RFC 6038             Reflect Octets & Symmetric Size        October 2010


    +-------------------+----------------------+---------------------+
    | Octets in:        | Unauthenticated Mode | Auth/Encrypted Mode |
    +-------------------+----------------------+---------------------+
    | Reflector Header  | 41                   | 112                 |
    | Sender Header     | 14                   | 48                  |
    | Truncated Padding | 27                   | 64                  |
    +-------------------+----------------------+---------------------+

                       TWAMP-Test Padding Truncation

   When using the Reflect Octets mode simultaneously with the truncation
   process that TWAMP recommends in Section 4.2.1 of [RFC5357], the
   Session-Sender MUST append at least 27 octets of padding plus the
   Length of the padding to reflect octets when operating in
   Unauthenticated mode.  The Session-Sender MUST append at least 64
   octets of padding plus the Length of the padding to reflect octets
   when operating in Authenticated and Encrypted modes.

Notes:

Incorrect header sizes (104 instead of 112) and the required padding size (56 instead of 64) for modes with authentication and encryption.

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