[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 RFC 6038

Network Working Group                                          A. Morton
Internet-Draft                                             L. Ciavattone
Updates: 5357 (if approved)                                    AT&T Labs
Intended status: Standards Track                          April 19, 2010
Expires: October 21, 2010


           TWAMP Reflect Octets and Symmetrical Size Features
                draft-ietf-ippm-twamp-reflect-octets-05

Abstract

   The IETF has completed its work on the core specification of TWAMP -
   the Two-Way Active Measurement Protocol.  This memo describes two
   closely-related features for TWAMP: an optional capability where the
   responder host returns some of the command octets or padding octets
   to the controller, and an optional sender packet format that ensures
   equal test packet sizes are used in both directions.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 21, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal



Morton & Ciavattone     Expires October 21, 2010                [Page 1]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.































Morton & Ciavattone     Expires October 21, 2010                [Page 2]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Purpose and Scope  . . . . . . . . . . . . . . . . . . . . . .  4
   3.  TWAMP Control Extensions . . . . . . . . . . . . . . . . . . .  5
     3.1.  Connection Setup with New Features . . . . . . . . . . . .  5
     3.2.  Reflect Octets: Request-TW-Session Packet Format . . . . .  6
     3.3.  Reflect Octets: Accept Session Packet Format . . . . . . .  8
     3.4.  Additional considerations  . . . . . . . . . . . . . . . .  9
   4.  Extended TWAMP Test  . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Sender Behavior  . . . . . . . . . . . . . . . . . . . . . 10
       4.1.1.  Packet Timings . . . . . . . . . . . . . . . . . . . . 10
       4.1.2.  Reflect Octets: Packet Formats and Contents  . . . . . 10
       4.1.3.  Reflect Octets: Interaction with Padding Truncation  . 12
       4.1.4.  Symmetrical Size: Session-Sender Packet Format . . . . 13
       4.1.5.  Symmetrical Size AND Reflect Octets:
               Session-Sender Packet Format . . . . . . . . . . . . . 13
     4.2.  Reflector Behavior . . . . . . . . . . . . . . . . . . . . 14
       4.2.1.  Reflect Octets: Session-Reflector Packet Format
               and Contents . . . . . . . . . . . . . . . . . . . . . 15
       4.2.2.  Symmetrical Size: Session-Reflector Packet Format  . . 16
       4.2.3.  Symmetrical Size AND Reflect Octets:
               Session-Sender Packet Format . . . . . . . . . . . . . 16
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  Registry Specification . . . . . . . . . . . . . . . . . . 17
     6.2.  Registry Management  . . . . . . . . . . . . . . . . . . . 17
     6.3.  Experimental Numbers . . . . . . . . . . . . . . . . . . . 17
     6.4.  Registry Contents  . . . . . . . . . . . . . . . . . . . . 17
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

















Morton & Ciavattone     Expires October 21, 2010                [Page 3]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


1.  Introduction

   The IETF has completed its work on the core specification of TWAMP -
   the Two-Way Active Measurement Protocol [RFC5357].  TWAMP is an
   extension of the One-way Active Measurement Protocol, OWAMP
   [RFC4656].  The TWAMP specification gathered wide review as it
   approached completion, and the by-products were several
   recommendations for new features in TWAMP.  There are a growing
   number TWAMP implementations at present, and wide-spread usage is
   expected.  There are even devices that are designed to test
   implementations for protocol compliance.

   This memo describes two closely-related features for TWAMP.

   One is the OPTIONAL capability for the responder host to return a
   limited number of unassigned (padding) octets to the Control-Client
   or Session-Sender entities.  With this capability, the Control-Client
   or Session-Sender can embed octets of information it deems useful and
   have the assurance that the corresponding reply/test packet will
   contain that information when it is reflected and returned (by the
   Server or Session-Reflector.

   The memo also adds an OPTIONAL capability to assure that reflected
   test packets are the same size in both directions of transmission.
   This is accomplished by specifying a new TWAMP-Test Session-Sender
   packet format.

   This memo is an update to the TWAMP core protocol specified in
   [RFC5357].  Measurement systems are not required to implement the
   features described in this memo to claim compliance with [RFC5357].

   Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set
   to zero by senders and MUST be ignored by receivers.  Also, the HMAC
   (Hashed Message Authentication Code) MUST be calculated as defined in
   Section 3.2 of [RFC4656].


2.  Purpose and Scope

   The purpose of this memo is to define two OPTIONAL closely-related
   features for TWAMP [RFC5357].  The features enhance the TWAMP
   responder's capabilities to perform simple operations on control and
   test packets: the reflection of octets or padding and symmetrical
   sizes of fields in the TWAMP-Test packets.  Motivations include
   permitting the controller host to tag packets with an index for
   simplified identification, and/or assert that the same size test
   packets will be used in each direction.




Morton & Ciavattone     Expires October 21, 2010                [Page 4]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   The scope of the memo is limited to specifications of the following
   features:

   o  Reflect Octets: the capability of the Server/Session-Reflector to
      reflect specific octets back to the Client/Session-Sender.

   o  Symmetrical Size: the capability to ensure that TWAMP-Test
      protocol uses the same packet size in both directions through
      support of a new TWAMP-Test Session-Sender test packet format in
      both the Session-Sender and the Session-Reflector.  Only the
      Session-Sender test packet format is new.

   This memo extends the modes of operation through assignment of two
   new values in the Modes Field (see section 3.1 of[RFC4656] for the
   format of the Server Greeting message), while retaining backward
   compatibility with the core TWAMP [RFC5357] implementations.  The two
   new values correspond to the two features defined in this memo.

   When the Server and Control-Client have agreed to use the Reflect
   Octets mode during control connection setup, then the Control-Client,
   the Server, the Session-Sender, and the Session-Reflector MUST all
   conform to the requirements of that mode, as identified below.

   When the Server and Control-Client have agreed to use the Symmetrical
   Size mode during control connection setup, then the Control-Client,
   the Server, the Session-Sender, and the Session-Reflector MUST all
   conform to the requirements of that mode, as identified below.


3.  TWAMP Control Extensions

   TWAMP-Control protocol [RFC5357] uses the Modes Field to identify and
   select specific communication capabilities, and this field is a
   recognized extension mechanism.  The following sections describe two
   such extensions.

3.1.  Connection Setup with New Features

   TWAMP connection establishment follows the procedure defined in
   section 3.1 of [RFC4656] and section 3.1 of [RFC5357].  The new
   features require two new bit positions (and values) to identify the
   ability of the Server/Session-Reflector to reflect specific octets
   back to the Control-Client/Session-Sender, and to support the new
   Session-Sender packet format in TWAMP-Test Protocol.  With this added
   feature, the complete set of TWAMP Modes Field bit positions and
   values would be as follows:





Morton & Ciavattone     Expires October 21, 2010                [Page 5]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   Value  Description             Reference/Explanation
   0      Reserved
   1      Unauthenticated         RFC4656, Section 3.1
   2      Authenticated           RFC4656, Section 3.1
   4      Encrypted               RFC4656, Section 3.1
   8      Unauth. TEST protocol,  RFC5681, Section 3.1
          Encrypted CONTROL
   16     Individual Session      RFC????, Section 3.1
          Control
   --------------------------------------------------------
   xxx    Reflect Octets          new bit position (X)
          Capability
   yyy    Symmetrical Size        new bit position (Y)
          Sender Test Packet Format


   In the original OWAMP Modes Field, setting bit positions 0, 1 or 2
   indicated the security mode of the Control protocol, and the Test
   protocol inherited the same mode (see section 4 of [RFC4656]).  In
   [RFC5618], bit position 3 allows unauthenticated TWAMP Test protocol
   to be used with encryption on the TWAMP-Control protocol in a mixed
   mode of operation.

   The Server sets one or both of the new bit positions (X and Y) in the
   Modes Field of the Server Greeting message to indicate its
   capabilities and willingness to operate in either of these modes (or
   both) if desired.

   >>>IANA: change xxx, yyy, X, Y, and RFC???? to the assigned values
   <<<

   If the Control-Client intends to operate all test sessions invoked
   with this control connection using one or both of the new modes, it
   MUST set the Mode Field bit corresponding to each function in the
   Setup Response message.  With this and other extensions, the Control-
   Client MAY set multiple Mode Field bits in the Setup Response
   message.

3.2.  Reflect Octets: Request-TW-Session Packet Format

   The bits designated for the Reflect Octets feature in the Request-TW-
   Session command are as shown in the packet format below.









Morton & Ciavattone     Expires October 21, 2010                [Page 6]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      5        |  MBZ  | IPVN  |  Conf-Sender  | Conf-Receiver |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Number of Schedule Slots                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .           ... Many fields (66 octets) not shown ...           .
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Padding Length  (4 octets)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Start Time, (8 octets)                   |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Timeout, (8 octets)                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Type-P Descriptor                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Octets to be reflected    |  Length of padding to reflect |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       MBZ (4 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                       HMAC (16 octets)                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The "Padding Length" Field *continues* to specify the number of
   padding octets that the Session-Sender will append to ALL TWAMP-Test
   packets associated with this test session.  See below for
   considerations on the minimum length of the padding octets, following
   the definitions of the two new fields that follow the Type-P
   Descriptor.

   Note that the number of padding octets appended to the Session-
   Reflector's test packet depends on support for the RECOMMENDED
   truncation process in TWAMP section 4.2.1 [RFC5357].

   The "Octets to be reflected" Field SHALL be 2 octets long, as shown
   and contains the octets that the Server MUST reflect in the Accept
   Session message as specified below.

   The "Length of padding to reflect" Field SHALL be 2 octets long, and



Morton & Ciavattone     Expires October 21, 2010                [Page 7]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   contain an unsigned binary value in units of octets.  This field
   communicates the length of the padding in the TWAMP-Test Packet that
   the Session-Sender expects to be reflected, and the length of octets
   that the Session-Reflector SHALL return in include in its TWAMP-Test
   packet format (see section 4.2).  By including this length field in
   the Request-TW-Session message, a Server is able to determine if it
   can comply with a specific request to reflect padding in the TWAMP-
   Test packets, and to arrange for the Session-Reflector processing in
   advance.

   The "Padding Length" SHOULD be >= 27 octets when specifying a test
   session using the Unauthenticated TWAMP-Test mode, to allow for the
   RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357].

   The "Padding Length" SHOULD be >= 56 octets when specifying a test
   session using the Authenticated or Encrypted TWAMP-Test modes, to
   allow for the RECOMMENDED truncation process in TWAMP section 4.2.1
   [RFC5357].

   The "Padding Length" SHALL be > the "Length of padding to reflect"
   when specifying a test session using the OPTIONAL Reflect Octets
   mode.

   In Unauthenticated TWAMP-Test mode, the "Padding Length" SHALL be >=
   27 + "Length of padding to reflect" octets when specifying a test
   session using BOTH the OPTIONAL Reflect Octets mode and the
   RECOMMENDED truncation process in TWAMP section 4.2.1 [RFC5357].

   In Authenticated or Encrypted TWAMP-Test modes, the "Padding Length"
   SHALL be >= 56 + "Length of padding to reflect" octets when
   specifying a test session using BOTH the OPTIONAL Reflect Octets mode
   and the RECOMMENDED truncation process in TWAMP section 4.2.1
   [RFC5357].

3.3.  Reflect Octets: Accept Session Packet Format

   The bits designated for the Reflect Padding feature in the Accept
   Session command are as shown in the packet format below.













Morton & Ciavattone     Expires October 21, 2010                [Page 8]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Accept     |      MBZ      |            Port               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
   |                                                               |
   |                        SID (16 octets)                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Reflected octets        |         Server octets         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       MBZ (8 octets)                          |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                       HMAC (16 octets)                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The "Reflected octets" field SHALL contain the octets from the
   Request-TW-Session "Octets to be reflected" Field, and be 2 octets
   long, as shown.

   The "Server octets" field SHALL contain information that the Server
   intends to be returned in the TWAMP-Test packet padding to-be-
   reflected Field, OR SHALL be zero, and be 2 octets long, as shown.
   Although the Server determines the SID, this field is very long (16
   octets) and does not normally appear in TWAMP-Test packets.

   When supporting the RECOMMENDED truncation process in TWAMP section
   4.2.1 [RFC5357], IF calculations on the Padding lengths reveal that
   there are insufficient octets supplied to produce equal-length
   Session-Sender and Session-Reflector test packets, then the Accept
   Field MUST be set to 3 = some aspect of the request is not supported.

3.4.  Additional considerations

   The value of the Modes Field sent by the Server in the Server
   Greeting message is the bit-wise OR of the mode values that it is
   willing to support during this session.

   With the publication of this memo as an RFC, the last 7 bit positions
   of the Modes 32-bit Field are used.  A Control-Client conforming to
   this extension of [RFC5357] MAY ignore the values in the higher bits
   of the Modes Field, or it MAY support other features that are



Morton & Ciavattone     Expires October 21, 2010                [Page 9]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   communicated in those bit positions.  The other bits are available
   for future protocol extensions.


4.  Extended TWAMP Test

   The TWAMP test protocol is similar to the OWAMP [RFC4656] test
   protocol with the exception that the Session-Reflector transmits test
   packets to the Session-Sender in response to each test packet it
   receives.  TWAMP section 4[RFC5357] defines two additional test
   packet formats for packets transmitted by the Session-Reflector.  The
   appropriate format depends on the security mode chosen.  The new
   modes specified here utilize some of the padding octets within each
   test packet format, or require truncation of those octets depending
   on the security mode in use.

4.1.  Sender Behavior

   This section describes extensions to the behavior of the TWAMP
   Session-Sender.

4.1.1.  Packet Timings

   The Send Schedule is not utilized in TWAMP, and this is unchanged in
   this memo.

4.1.2.  Reflect Octets: Packet Formats and Contents

   The Session-Sender packet format and content follow the same
   procedure and guidelines as defined in section 4.1.2 of [RFC4656] (as
   indicated in section 4.1.2 of TWAMP [RFC5357]).

   The Reflect octets mode re-designates the original TWAMP-Test (and
   OWAMP-Test) Packet Padding Field (see section 4.1.2 of [RFC4656]), as
   shown below for unauthenticated mode:
















Morton & Ciavattone     Expires October 21, 2010               [Page 10]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Timestamp                            |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Error Estimate        |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                  Packet Padding (to be reflected)             |
   .               (length in octets specified in command)         .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                  Additional Packet Padding                    .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The "Packet Padding (to be reflected)" Field SHALL correspond to the
   length of octets specified in the Request-TW-Session "Length of
   padding to reflect" Field to this test session.  These are the octets
   that the Session-Sender expects will be returned by the Session-
   Reflector.

   The length of the "Additional Packet Padding" Field is the difference
   between two fields in the Request-TW-Session command, as follows:

   "Additional Packet Padding", in octets =

   "Padding Length" - "Length of padding to reflect"

   One possible use of the first 4 octets of the "Packet Padding (to be
   reflected)" Field is shown below:

















Morton & Ciavattone     Expires October 21, 2010               [Page 11]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |         Server octets         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Client octets          |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                  Packet Padding (to be reflected)             |
   .               (length in octets specified elsewhere)          .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   In this example, the "Client octets" and the "Server octets" fields
   contain the same information that the Client and Server exchanged in
   the Request-TW-Session and Accept-Session messages corresponding to
   this specific test session.  These octets would be reflected the same
   as the rest of the "Packet Padding (to be reflected)" Field.

4.1.3.  Reflect Octets: Interaction with Padding Truncation

   When the Reflect Octets mode is selected, and the RECOMMENDED
   truncation process in TWAMP section 4.2.1 [RFC5357] is supported, the
   Session-Sender MUST anticipate a minimum padding required to achieve
   equal size test packets in both directions.  The amount of padding
   needed to achieve symmetrical packet size depends on BOTH the
   security mode (Unauthenticated/Authenticated/Encrypted) and whether
   the Reflect Octets mode is selected simultaneously.

   When using the RECOMMENDED truncation process in TWAMP section 4.2.1
   [RFC5357] alone, 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:

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

                       TWAMP-Test Padding Trucation

   When using the Reflect Octets mode simultaneously with the



Morton & Ciavattone     Expires October 21, 2010               [Page 12]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   RECOMMENDED truncation process in TWAMP section 4.2.1 [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.

4.1.4.  Symmetrical Size: Session-Sender Packet Format

   When the Symmetrical Size mode is selected, the Session-Sender SHALL
   use the following TWAMP-Test Packet Format in Unauthenticated mode:

   Unauthenticated Mode
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Timestamp                            |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Error Estimate        |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                                                               |
   |                         MBZ (27 octets)                       |
   |                                                               |
   |                                                               |
   |                                                               |
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |                                               |
   +-+-+-+-+-+-+-+-+                                               +
   .                                                               .
   .                        Packet Padding                         .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This feature REQUIRES only a new Session-Sender test packet format,
   the Session-Reflector test packet format is unchanged.

4.1.5.  Symmetrical Size AND Reflect Octets: Session-Sender Packet
        Format

   When BOTH the Symmetrical Size mode and the Reflect Octets mode are
   selected, the Session-Sender SHALL use the following TWAMP-Test
   Packet Format in Unauthenticated mode:





Morton & Ciavattone     Expires October 21, 2010               [Page 13]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   Unauthenticated Mode
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Timestamp                            |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Error Estimate        |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   |                                                               |
   |                         MBZ (27 octets)                       |
   |                                                               |
   |                                                               |
   |                                                               |
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |                                               |
   +-+-+-+-+-+-+-+-+                                               +
   |                  Packet Padding (to be reflected)             |
   .               (length in octets specified in command)         .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                  Additional Packet Padding                    .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   In this combined mode, the Packet Padding to be reflected follows the
   27 MBZ octets.  In Authenticated or Encrypted modes, the Packet
   Padding to be reflected follows the 56 MBZ octets.

4.2.  Reflector Behavior

   The TWAMP Reflector follows the procedures and guidelines in section
   4.2 of [RFC5357], with the following additional functions:

   o  Reflect Octets mode: Designated octets in the "Packet Padding (to
      be reflected)" field of the Session-Sender's test packet MUST be
      included in the Session-Reflector's test packet.

   o  Symmetrical Size mode: The Session-Reflector MUST operate using
      the Session_Reflector Packet Format defined in section 4.1.4,
      where the Padding Octets are separated from the information
      fields.






Morton & Ciavattone     Expires October 21, 2010               [Page 14]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


4.2.1.  Reflect Octets: Session-Reflector Packet Format and Contents

   The Reflect Padding feature re-designates the packet padding field,
   as shown below.  When the Reflect Octets mode is selected, the
   Session-Sender SHALL use the following TWAMP-Test Packet Format in
   Unauthenticated mode:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sequence Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Timestamp                            |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Error Estimate        |           MBZ                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Receive Timestamp                    |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Sender Sequence Number                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Sender Timestamp                         |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Sender Error Estimate    |           MBZ                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Sender TTL   |         Packet Padding (from Session-Sender)  |
    +-+-+-+-+-+-+-+-+                                               +
    .                                                               .
    +                                               +-+-+-+-+-+-+-+-+
    |          Packet Padding (from Session-Sender) |               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
    |                                                               |
    |                                                               |
    .                  Additional Packet Padding                    .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   The "Packet Padding (from Session-Sender)" field MUST be the same
   octets as the "Packet Padding (to be reflected)" field in the
   Session-Sender's test packet, and therefore MUST conform to the
   length specified in the Request-TW-Session message.

   When simultaneously using the RECOMMENDED truncation process in TWAMP
   section 4.2.1 [RFC5357] AND Reflect octets mode, the Session-
   Reflector MUST reflect the designated octets from the Session-
   Sender's test packet in the "Packet Padding (from Session-Sender)"
   Field, and MAY re-use additional Packet Padding from the Session-
   Sender.  The Session-Reflector MUST truncate the padding such that



Morton & Ciavattone     Expires October 21, 2010               [Page 15]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   the highest number octets are discarded, and the test packet length
   equals the Session-Sender's packet length.  When using the
   RECOMMENDED truncation process, the Session-Reflector MUST truncate
   exactly 27 octets of padding in Unauthenticated mode, and exactly 56
   octets in Authenticated and Encrypted modes.

   The Session-Reflector MAY re-use the Sender's Packet Padding (since
   the requirements for padding generation are the same for each).

4.2.2.  Symmetrical Size: Session-Reflector Packet Format

   When Symmetrical Size mode is selected, the Session-Sender packet
   formats for unauthenticated and authenticated/encrypted modes are
   identical to the core TWAMP specification, section 4.2.1 of
   [RFC5357].  Thus, the Session-Reflector test packet format is
   unchanged.

   The Session-Reflector MUST construct its test packet using the
   information in the Session-Sender's test packet.  The length of the
   Session-Reflector's test packet SHALL equal the length of the
   Session-Sender's test packet.

4.2.3.  Symmetrical Size AND Reflect Octets: Session-Sender Packet
        Format

   When BOTH the Symmetrical Size mode and the Reflect Octets mode are
   selected, the Session-Reflector MUST operate using the
   Session_Reflector Packet Format defined in section 4.1.5, where the
   Padding Octets are separated from the information fields, and the
   Padding to be Reflected field precedes the Additional Padding.

   The Session-Reflector SHALL use the same TWAMP-Test Packet Format as
   specified in section 4.2.1 above.


5.  Security Considerations

   These extended modes of operation do not appear to permit any new
   attacks on hosts communicating with core TWAMP [RFC5357].

   The security considerations that apply to any active measurement of
   live networks are relevant here as well.  See [RFC4656] and
   [RFC5357].


6.  IANA Considerations

   This memo adds two modes to the IANA registry for the TWAMP Modes



Morton & Ciavattone     Expires October 21, 2010               [Page 16]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   Field, and describes behavior when the new modes are used.  This
   field is a recognized extension mechanism for TWAMP.

6.1.  Registry Specification

   IANA has created a TWAMP-Modes registry (as requested in [RFC5618]).
   TWAMP-Modes are specified in TWAMP Server Greeting messages and
   Set-up Response messages, as described in section 3.1 of [RFC5357],
   consistent with section 3.1 of [RFC4656], and extended by this memo.
   Modes are indicated by setting bits in the 32-bit Modes field that
   correspond to values in the Modes registry.  For the TWAMP-Modes
   registry, we expect that new features will be assigned increasing
   registry values that correspond to single bit positions, unless there
   is a good reason to do otherwise (more complex encoding than single
   bit positions may be used in the future, to access the 2^32 value
   space).

6.2.  Registry Management

   This registry must be updated only by "IETF Consensus" as specified
   in [RFC5226](an RFC documenting registry use that is approved by the
   IESG).

6.3.  Experimental Numbers

   No experimental values are currently assigned for the Modes Registry.

6.4.  Registry Contents

   TWAMP Modes Registry is recommended to be augmented as follows:





















Morton & Ciavattone     Expires October 21, 2010               [Page 17]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   Value  Description             Semantics Definition
   0      Reserved

   1      Unauthenticated         RFC4656, Section 3.1

   2      Authenticated           RFC4656, Section 3.1

   4      Encrypted               RFC4656, Section 3.1

   8      Unauth. TEST protocol,  RFC5618, Section 3.1 (3)
          Auth. CONTROL
   16     Individual Session      RFC????, Section 3.1
          Control                 bit position (4)
   --------------------------------------------------------
   xxx    Reflect Octets          this memo, section 3.1
          Capability              new bit position (X)
   yyy    Symmetrical Size        this memo, section 3.1
          Sender Test Packet Format new bit position (Y)


   The suggested values are

   X=5, xxx=32

   Y=6, yyy=64


7.  Acknowledgements

   The authors thank Steve Baillargeon, Walt Steverson, and Stina Ross
   for helpful review and comments.


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.




Morton & Ciavattone     Expires October 21, 2010               [Page 18]

Internet-Draft       Reflect Octets & Symmetric Size          April 2010


   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
              Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
              August 2009.

8.2.  Informative References


Authors' Addresses

   Al Morton
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748
   USA

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acmorton@att.com
   URI:   http://home.comcast.net/~acmacm/


   Len Ciavattone
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748
   USA

   Phone: +1 732 420 1239
   Fax:
   Email: lencia@att.com
   URI:
















Morton & Ciavattone     Expires October 21, 2010               [Page 19]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/