





Network Working Group                                          A. Morton
Request for Comments: 5618                                     AT&T Labs
Updates: 5357                                                 K. Hedayat
Category: Standards Track                                           EXFO
                                                             August 2009


Mixed Security Mode for the Two-Way Active Measurement Protocol (TWAMP)

Abstract

   This memo describes a simple extension to TWAMP (the Two-Way Active
   Measurement Protocol).  The extension adds the option to use
   different security modes in the TWAMP-Control and TWAMP-Test
   protocols simultaneously.  The memo also describes a new IANA
   registry for additional features, called the TWAMP Modes registry.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents in effect on the date of
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

   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.




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Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................3
   2. Purpose and Scope ...............................................3
   3. TWAMP Control Extensions ........................................3
      3.1. Extended Control Connection Setup ..........................3
   4. Extended TWAMP Test .............................................5
      4.1. Sender Behavior ............................................5
           4.1.1. Packet Timings ......................................5
           4.1.2. Packet Format and Content ...........................5
      4.2. Reflector Behavior .........................................6
   5. Security Considerations .........................................6
   6. IANA Considerations .............................................6
      6.1. Registry Specification .....................................6
      6.2. Registry Management ........................................6
      6.3. Experimental Numbers .......................................7
      6.4. Initial Registry Contents ..................................7
   7. Acknowledgements ................................................7
   8. Normative References ............................................7

1.  Introduction

   The Two-Way Active Measurement Protocol (TWAMP) [RFC5357] 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 is a growing number
   of TWAMP implementations at present, and widespread usage is
   expected.  There are even devices that are designed to test
   implementations for protocol compliance.

   This memo describes a simple extension for TWAMP: the option to use
   different security modes in the TWAMP-Control and TWAMP-Test
   protocols (mixed security mode).  It also describes a new IANA
   registry for additional features, called the TWAMP Modes registry.

   When the Server and Control-Client have agreed to use the mixed
   security 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 this mode as described in
   Sections 3, 4, and 5.

   This memo updates [RFC5357].







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1.1.  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].

2.  Purpose and Scope

   The purpose of this memo is to describe and specify an extension for
   TWAMP [RFC5357], and to request the establishment of a registry for
   future TWAMP extensions.

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

   o  Extension of the modes of operation through assignment of one new
      value in the Modes field (see Section 3.1 of [RFC4656]), while
      retaining backward compatibility with TWAMP [RFC5357]
      implementations.  This value adds the OPTIONAL ability to use
      different security modes in the TWAMP-Control and TWAMP-Test
      protocols.  The motivation for this extension is to permit the
      low-packet-rate TWAMP-Control protocol to utilize a stronger mode
      of integrity protection than that used in the TWAMP-Test protocol.

3.  TWAMP Control Extensions

   The TWAMP-Control protocol is a derivative of the OWAMP-Control
   protocol, and coordinates a two-way measurement capability.  All
   TWAMP-Control messages are similar in format and follow similar
   guidelines to those defined in Section 3 of [RFC4656], with the
   exceptions described in TWAMP [RFC5357] and in the following
   sections.

   All OWAMP-Control messages apply to TWAMP-Control, except for the
   Fetch-Session command.

3.1.  Extended Control Connection Setup

   TWAMP-Control connection establishment follows the same procedure
   defined in Section 3.1 of [RFC4656].  This extended mode assigns one
   new bit position (and value) to allow the Test protocol security mode
   to operate in Unauthenticated mode, while the Control protocol
   operates in Encrypted mode.  With this extension, the complete set of
   TWAMP Mode values are as follows:








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   Value  Description             Reference/Explanation

   0      Reserved

   1      Unauthenticated         RFC 4656, Section 3.1

   2      Authenticated           RFC 4656, Section 3.1

   4      Encrypted               RFC 4656, Section 3.1

   8      Unauth. TEST protocol,  new bit position (3)
          Encrypted CONTROL


   In the original OWAMP and TWAMP Modes field, setting bit position 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 this extension to TWAMP, when the Control-Client sets Modes Field
   bit position 3, it SHALL discontinue the inheritance of the security
   mode in the Test protocol, and each protocol's mode SHALL be as
   specified below.  When the desired TWAMP-Test protocol mode is
   identical to the Control Session mode, the corresponding Modes Field
   bit (position 0, 1, or 2) SHALL be set by the Control-Client.  The
   table below gives the various combinations of integrity protection
   that are permissible in TWAMP (with this extension).  The TWAMP-
   Control and TWAMP-Test protocols SHALL use the mode in each column
   corresponding to the bit position set in the Modes Field.

   --------------------------------------------------------
   Protocol | Permissible Mode Combinations (Modes bit set)
   --------------------------------------------------------
   Control  |    Unauth.(0)|  Auth. == Encrypted (1,2,3)
   --------------------------------------------------------
            |    Unauth.(0)|         Unauth.  (3)
            -----------------------------------------------
   Test     |              |          Auth.(1)
            -----------------------------------------------
            |              |        Encrypted (2)
   --------------------------------------------------------

   Note that the TWAMP-Control protocol security measures are identical
   in the Authenticated and Encrypted Modes.  Therefore, only one new
   bit position (3) is needed to convey the single mixed security mode.

   The value of the Modes Field sent by the Server in the Server-
   Greeting message is the bit-wise OR of the modes (bit positions) that
   it is willing to support during this session.  Thus, the last four



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   bits of the 32-bit Modes Field are used.  When no other features are
   activated, the first 28 bits MUST be zero.  A client conforming to
   this extension of [RFC5357] MAY ignore the values in the first 28
   bits of the Modes Field, or it MAY support other features that are
   communicated in these bit positions.

   Other ways in which TWAMP extends OWAMP are described in [RFC5357].

4.  Extended TWAMP Test

   The TWAMP-Test protocol is similar to the OWAMP-Test protocol
   [RFC4656] with the exception that the Session-Reflector transmits
   test packets to the Session-Sender in response to each test packet it
   receives.  TWAMP [RFC5357] defines two different test packet formats:
   one for packets transmitted by the Session-Sender and one for packets
   transmitted by the Session-Reflector.  As with the OWAMP-Test
   protocol, there are three security modes that also determine the test
   packet format: unauthenticated, authenticated, and encrypted.  This
   TWAMP extension makes it possible to use TWAMP-Test Unauthenticated
   mode regardless of the mode used in the TWAMP-Control protocol.

   When the Server has identified the ability to support the mixed
   security mode, the Control-Client has selected the mixed security
   mode in its Set-Up-Response, and the Server has responded with a zero
   Accept field in the Server-Start message, these extensions are
   REQUIRED.

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 there are no
   extensions defined in this memo.

4.1.2.  Packet Format and Content

   The Session-Sender packet format and content MUST follow the same
   procedure and guidelines as defined in Section 4.1.2 of [RFC4656] and
   Section 4.1.2 of [RFC5357], with the following exceptions:

   o  the send schedule is not used, and

   o  the Session-Sender MUST support the mixed security mode
      (Unauthenticated TEST, Encrypted CONTROL, value 8, bit position 3)
      defined in Section 3.1 of this memo.



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4.2.  Reflector Behavior

   The TWAMP Session-Reflector is REQUIRED to follow the procedures and
   guidelines in Section 4.2 of [RFC5357], with the following
   extensions:

   o  the Session-Reflector MUST support the mixed security mode
      (Unauthenticated TEST, Encrypted CONTROL, value 8, bit position 3)
      defined in Section 3.1 of this memo.

5.  Security Considerations

   The extended mixed mode of operation permits stronger security/
   integrity protection on the TWAMP-Control protocol while
   simultaneously emphasizing accuracy or efficiency on the TWAMP-Test
   protocol, thus making it possible to increase overall security when
   compared to the previous options (when resource constraints would
   have forced less security for TWAMP-Control and conditions are such
   that use of unauthenticated TWAMP-Test is not a significant concern).

   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 one security mode bit position/value beyond those in
   the OWAMP-Control specification [RFC4656], and describes behavior
   when the new mode is used.  According to this document, IANA created
   a registry for the TWAMP Modes field.  This field is a recognized
   extension mechanism for TWAMP.

6.1.  Registry Specification

   IANA created a TWAMP Modes registry.  TWAMP Modes are specified in
   TWAMP Server Greeting messages and Set-up Response messages
   consistent with Section 3.1 of [RFC4656] and Section 3.1 of
   [RFC5357], and extended by this memo.  Modes are currently indicated
   by setting single bits in the 32-bit Modes Field.  However, more
   complex encoding may be used in the future.  Thus, this registry can
   contain a total of 2^32 possible assignments.

6.2.  Registry Management

   Because the TWAMP Modes registry can contain a maximum of 2^32
   values, and because TWAMP is an IETF protocol, this registry must be
   updated only by "IETF Review" as specified in [RFC5226] (an RFC
   documenting registry use that is approved by the IESG).  For the



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   TWAMP Modes registry, we expect that new features will be assigned
   using monotonically increasing single bit positions and in the range
   [0-31], 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).

6.3.  Experimental Numbers

   No experimental values are currently assigned for the Modes Registry.

6.4.  Initial Registry Contents

   TWAMP Modes Registry
   Value  Description             Semantics Definition
   0      Reserved                RFC 5618

   1      Unauthenticated         RFC 4656, Section 3.1

   2      Authenticated           RFC 4656, Section 3.1

   4      Encrypted               RFC 4656, Section 3.1

   8      Unauth. TEST protocol,  RFC 5618, Section 3.1
          Encrypted CONTROL

7.  Acknowledgements

   The authors would like to thank Len Ciavattone and Joel Jaeggli for
   helpful review and comments.

8.  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.

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





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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/


   Kaynam Hedayat
   EXFO
   285 Mill Road
   Chelmsford, MA  01824
   USA

   Phone: +1 978 367 5611
   Fax:   +1 978 367 5700
   EMail: kaynam.hedayat@exfo.com
   URI:   http://www.exfo.com/



























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